2007 Annual Report of the ASSOCIATION EURATOM/IST, ASSOCIATED LABORATORY WITH FCT Centro de Fusão Nuclear e Centro de Física dos Plasmas

ASSOCIATION EURATOM/IST ASSOCIATED LABORATORY WITH FCT Centro de Fusão Nuclear Centro de Física dos Plasmas 2007 ANNUAL REPORT Figures on cover (from left to right, and top to bottom) Capacitively coupled radio-frequency plasma reactor, running a discharge in N 2 . Prototype of a 400 MSPS, 14-bit, 8-channel transient recorder board for JET. QuickPIC simulation showing a plasma wave and a laser entering the plasma. Plasma position reflectometer with ITER: proposed ex-vessel waveguide routings for gaps 4, 5, and 6. Front view of the IST Cluster. Centro de Fusão N uclea r Centro de Física dos Plasmas INSTITUTO SUPERIOR TÉCNICO CENTRO DE FUSÃO NUCLEAR CENTRO DE FÍSICA DOS PLASMAS 2007 ANNUAL REPORT Activities carried out in the frame of: • The Contract of Association EURATOM/IST on Plasma Fusion Research • The Contract of Associated Laboratory with FCT on Plasma Physics and Engineering IST, July 2008 i CONTENTS Page A. FOREWORD 1. Introduction …………………………………………………………………………………….…… 1 1.1. Foreword ………………………………………………………………………..……………… 1 1.2. Fusion-related activities …………………………………...…………..………..…………........ 1 1.3. Associated Laboratory ……………………………………………………………………….… 2 1.4. Other projects …………………………………………………………………………………... 2 B. CONTROLLED NUCLEAR FUSION 1 2. Tokamak ISTTOK 2.1. Introduction ……………………………………………………………………………………. 5 2.2. Fusion-relevant materials ……………………………………………………………………… 5 2.3. Diagnostics …………………………………………………………………………………….. 7 2.4. Real-time control and data acquisition ………………………………………………………… 9 2.5. Plasma physics studies ………………………………………………………………………… 10 2.6. Organization of the ISTTOK joint experiment ………………………………………………... 12 3. Participation in the use of the JET facilities by the EFDA Associates 3.1. Introduction ……………………………………………………………………………………. 13 3.2. Operation …………………………………………………………………………………….… 13 3.3. Scientific exploitation ………………………………………………………………………….. 13 3.4. Performance enhancements ……………………………………………………………….…… 24 3.5. Management …………………………………………………………………………………… 26 4. Participation in the ITER project 4.1. Introduction ………………………………………………………………………………….… 27 4.2. Microwave reflectometry ……………………………………………………..…………….…. 27 4.3. Control and data acquisition ……………………………………………………………....…… 29 4.4. Quality assurance ………………………………………………………………………….…… 30 5. Participation in the ASDEX-Upgrade programme 5.1. Introduction …………………………………………………………………………………...... 31 5.2. Microwave reflectometry ………………… …………………………………………………….….... 31 5.3. Plasma physics studies ………………………………………………………………..….….… 33 6. Participation in the TJ-II programme 6.1. Introduction …………………………………………………………………………………...... 37 6.2. Microwave reflectometry ………………… …………………………………………………….….... 37 6.3. Edge physics ………………………………………………………………..…………….….… 37 7. Participation in the TCV programme 7.1. Introduction ………………………………………………………………………………..….... 39 7.2. X-Ray diagnostics ………………… ……………………………………………………...….….... 39 7.3. Advanced plasma control system ………………………………………………………...…..… 40 8. Collaboration with the Association EURATOM/CEA 8.1. Introduction …………………………………………………………………………………….. 43 8.2. Modelling of reflectometry experiments ……………………………………………………..… 43 8.3. Basic theory on plasma turbulence ……………………………………………………….….… 43 8.4. Lower hybrid current drive ………………………………….……………………………...….. 43 1 Activities carried out in the frame of the Contract of Association EURATOM/IST and the Contract of Associated Laboratory. ii 9. Other theory and modelling studies 9.1. Introduction ……………………………………………………………………………….….… 47 9.2. MHD stability studies ……..……………………………………………………………….…... 47 9.3. Modelling of tokamak equilibria with toroidal current reversal ……………………………..… 47 10. Other activities on control and data acquisition ………………………………………………....… 49 11. Keep-in-touch activities in inertial fusion energy 11.1. Introduction ………………………………………………………………………………….. 51 11.2. Fast ignition ……………………………………………………………………………. ……. 51 11.3. High intensity photonics ………………………………………………………………..…… 51 11.4. Plasma accelerators and intense radiation sources ……………………………………. …….. 51 12. Participation in the Fusion Technology Programme 12.1. Introduction ………………………………………………………………………………...... 53 12.2. Material characterization using nuclear techniques: titanium beryllide oxidation studies … 53 12.3. Task TW6-TPP-ERDEP - Studies of material erosion and redeposition in iter-relevant divertor target temperatures, plasma impact energies and divertor chamber geometries …… 53 13. Other fusion-related activities 13.1. Introduction ……………………………………………………………………….…….….... 55 13.2. Collaboration with IPP.CZ …………………………………………………………………... 55 13.3. Collaboration with IPP-Greisfwald ……………………………………………………….. … 55 13.4. Collaboration with Brazilian Institutions ………………………………………………….… 55 13.5. Collaboration with ENEA-Frascati ……………………………………………………..…… 56 13.6. Socio-economic studies ……………………………………………………………..……..… 56 13.7. Education and training …………………………………………………………………….… 57 13.8. Organization of the 17 th IAEA technical meeting on “Research Using Small Fusion Devices” ……………………………………………………………………………………... 57 13.9. Participation in the management of the EURATOM Fusion Programme ………...………… 57 13.10. Other management activities ………………………………………………………...….….. 57 C. TECHNOLOGIES OF PLASMAS AND HIGH POWER LASERS 2 14. Plasma theory and simulations 14.1. Introduction ……………………………………………………………………………….…. 59 14.2. White light parametric instabilities ………………………………………………………. …. 59 14.3. Lasers-plasma accelerators …………………………………………………………………... 60 14.4. Fast ignition and laser-solid interactions ………………………………………………….…. 62 14.5. Astro and space physics ……………………………………………………………………... 64 14.6. High performance computing ……………………………………………………………….. 65 14.7. Computational physics ………………………………………………………………………. 68 14.8. Radiation generation ………………………………………………………………………… 68 15. High density laser plasma physics 15.1. Introduction ………………………………………………………………………………...… 71 15.2. Design work for HiPER ………………………………………………………………..….…. 71 15.3. Analysis of results from laser-solid experiments on the vulcan PW ……………………...…. 71 15.4. Filamentation in laser ablation of solids ………………………………………………..….… 72 15.5. Integrated numerical design of laser-plasma experiments …………………………………… 72 16. High intensity photonics and experimental laser-plasma interactions 16.1. Introduction ……………………………………………………………………………….…. 75 16.2. High-power laser research and development …………………………………………….….. 75 16.3. Laser-plasma accelerators ……………………………………………………………….…... 76 16.4. Coherent x-ray sources ………………………………………………………………….…… 78 16.5. Laser-plasma interactions ……………………………………………………………….…… 80 16.6. Diagnostics …………………………………………………………………………….…….. 81 16.7. High-voltage pulse generator ………………………………………………..……………..... 83 2 Activities performed in the frame of the Contract of Associated Laboratory, out of the Contract of Association EURATOM/IST. iii 17. Fundamental physics and quantum computing 17.1. Introduction ……………………………………………………………………………….…. 85 17.2. Pioneer anomalous acceleration ……………………………………………………...……… 85 17.3. Alternative models of gravity …………………………………………………………...…… 85 17.4. Dark energy and dark matter ………………………………………………………………… 85 17.5. Putative violations of fundamental symmetries of nature …………………………………… 86 17.6. Quantum computing …………………………………………………………………….…… 86 18. Environmental engineering plasma laboratory 18.1. Introduction …………………………………………………………...……………………… 89 18.2. Plasma torches for environmental issues ……………………………………………..……… 89 18.3. Extraordinary phenomena in hydrogen plasmas …………………………………...………… 91 18.4. Improvement of plasma diagnostic techniques …………………………………….………… 92 19. Non-equilibrium kinetics and simulations of plasmas and afterglow plasmas 19.1. Introduction ………………………………………………………………………………...… 95 19.2. Kinetic study of the nitrogen afterglow ……………………………………………………… 95 19.3. Modeling of N 2 -O 2 afterglow plasmas for plasma sterilization and insight in elementary processes ……………………………………………………………………………...……… 95 19.4. Modeling of N 2 -CH 4 discharges and afterglow plasmas for planetary atmospheric studies and surface treatments ……………………………………………………………………...… 97 19.5. Theoretical modeling of hetero-geneous atomic recombination ……………………….….… 97 19.6. Modeling of kinetic and radiative processes in low-pressure, high-temperature plasmas …… 98 20. Modeling of plasma reactors 20.1. Introduction ……………………………………………………………………..………….… 101 20.2. Microwave-driven plasma reactor operated by an axial injection torch ………………..….… 101 20.3. Micro-plasma reactors …………………………………………………………………..….… 102 20.4. Capacitively coupled plasma reactor ………………………………………………………… 103 20.5. Inductively coupled plasma reactor …………………………………………………..……… 104 20.6. Surface-wave plasma reactors ……………………………………………………………...… 105 21. Plasma and electromagnetic propulsion 21.1. Introduction …………………………………………………………………..…………….… 107 21.2. Plasma propulsion ………………………………………………………………………….… 107 21.3. Electromagnetic propulsion ……………………………………………….……………….… 108 21.4. Research on fundamental problems of plasma physics …………………………………….… 109 21.5. Analytical glow discharge optical emission spectroscopy …………………….……..…….… 109 D. SCIENTIFIC OUTPUTS, PRIZES AND AWARDS 22. Publications, laboratorial prototypes, prizes and awards 22.1. Magnetic fusion ……………………..……………………………………………………...… 111 22.2. Technologies of plasmas and lasers ………………………………………….…………….… 121 1 1. INTRODUCTION F. Serra, C. Varandas, L.L. Alves (Editors) 1.1. FOREWORD This document presents the main activities carried out in 2007 in the frame of the Contract of Association (CoA) signed in 1990 between the European Atomic Energy Community (EURATOM) and “Instituto Superior Técnico” (IST), hereinafter referred to as Association EURATOM/IST, and of the Contract of Associated Laboratory on Plasma Physics and Engineering signed in 2001 by “Fundação para a Ciência e a Tecnologia” (FCT) and IST, hereinafter referred to as Associated Laboratory (AL). The CoA activities are described in chapters 2 to 13, while the AL activities are presented in chapters 2 to 10 and 13 to 21. Chapter 22 contains the list of publications, laboratorial prototypes, prizes and awards. The activities described in this document were mainly performed by “Centro de Fusão Nuclear” (CFN) and “Centro de Física de Plasmas” (CFP), two Research Units of IST (Figure 1.1). The other collaborating Institutions are presented in Figure 1.1 and Table 1.1. 1.2. FUSION-RELATED ACTIVITIES 1.2.1. Introduction The research and development activities on controlled nuclear fusion have been carried out according to the Contract of Association EURATOM/IST, which frames the Portuguese participation in the EURATOM Specific Research and Training Programme in the Field of Nuclear Fusion Energy, hereinafter referred as Community Fusion Programme. This Programme has as its long-term objective the development of a prototype commercial fusion power plant. It is presently implemented through several Agreements, in particular: (i) Contracts of Association signed between EURATOM and Institutions of the Member States of the European Union and Switzerland (Associates); (ii) the European Fusion Development Agreement (EFDA); and (iii) the Mobility Agreement, both signed by EURATOM and its Associates. The main European fusion-related event in 2007 was the approval by the Council, on March 27 th , of the statutes of the “European Joint Undertaking for ITER and the Development of Fusion Energy” (Fusion for Energy). This enterprise is the EU Domestic Agency for ITER and it is also in charge with the project-oriented DEMO activities as well as with the EU contribution for the Broader Approach, a bilateral agreement signed between the European Union and Japan, aiming at speeding up the development of fusion energy. Fusion for Energy entered into force on April 19 th and its first Director, Dr. Didier Gambier, started his functions on October 1 st 2007. In the meantime, the EURATOM Fusion Programme has started its re-organization taking into account the beginning of ITER construction and the enter into force Figure 1.1 – Organization of the Associated Laboratory and Association EURATOM/IST 2 of Fusion for Energy. Particular relevant for our activity is the new European Fusion Development Agreement (EFDA) and the new Contract of Association, which entered into force on January 1 st 2008. 1.2.2. Main projects of the Association EURATOM/IST The work programme of the Association EURATOM/IST included activities carried out in Portugal (mainly related with the tokamak ISTTOK) and abroad related with the operation and scientific exploitation of large and medium-sized tokamaks and stellarator (JET, ASDEX-Upgrade, TCV, and TJ-II) as well as with the design of the next generation fusion devices (ITER and W7-X). Its main projects in 2007 were:  Tokamak ISTTOK;  Participation in the collective use of the JET facilities by the EFDA Associates;  Participation in the ITER Project;  Participation in the ASDEX-UPGRADE Programme;  Participation in the TJ-II Programme;  Participation in the TCV Programme;  Collaboration with the Association EURATOM/CEA  Other activities on theory and modelling;  Other activities on control and data acquisition;  Keep-in-touch activities on inertial fusion energy;  Participation in the Fusion Technology Programme;  Other fusion-related activities 1 . Table 1.1 presents information about the responsible person(s) and the Institutions involved in each project. 1.3. ASSOCIATED LABORATORY The Associated Laboratory on Plasma Physics and Engineering has two thematic areas: o Controlled Nuclear Fusion; o Technologies of Plasmas and High-Power Lasers The first area includes the activities carried out by CFN and CFP staff in the frame of the projects of the Association EURATOM/IST, while the area on “Technologies of Plasmas and High Power Lasers” had in 2007 the following projects: • Plasma theory and simulations; • High density laser plasma physics; • Fundamental physics and quantum computing; • Environmental engineering plasma laboratory; • Nonequilibrium kinetics and simulation of plasmas and afterglow plasmas; • Modelling of plasma reactors; • Plasma and electromagnetic propulsion. 1.4. OTHER PROJECTS CFN and CFP have also developed in 2007 activities in the frame of the following projects 1 o Re-Equipment of the ISTTOK Laboratory (FCT 3 , C. Varandas, 2005-2007); o Re-Equipment of the CFN Microwave Laboratory (FCT, M.E. Manso, 2005-2007) o Cosmic Concordance (FCT, O. Bertolami, 2005- 2007); o A Mission to Test the Pioneer Anomaly (FCT, O. Bertolami, 2006-2009); o Estudos Teóricos de Ignição Rápida em Fusão Inercial (FCT, J. R. Davies, 2005 – 2007); o Relativistic Harmonic Generation in Underdense Plasmas (FCT, João Mendanha Dias, 2004-2007) o New Sub-cycle Rediation Sources in the Visible by Relativistic Mirror (FCT, João Mendanha Dias, 2005- 2007); o Tabletop Ultra-Intense XUV Sources for Femtobiology and Related Applications (TUIXS), (European Commission, M. Fajardo, 2005-2008); o Advanced Plasma Accelerators: Beam Optimization, Diagnostics and Applications, (FCT, N. Lopes, 2006- 2007); o Dos Choques Relativistas aos Lasers Ultra Intensos: Ciência das Elevadas Densidades de Energia, (FCT, L. Silva, 2005-2007); o European Laser Electron Controlled Acceleration in Plasmas to GeV Energy Range (European Commission L. Silva, 2006-2009); o Laboratório de Engenharia de Plasmas para Aplicações Ecológicas (FCT, C.M. Ferreira, 2005- 2007); o Plasmas HF de Grandes Dimensões para Aplicações Ambientais” (FCT, C. M. Ferreira, 2006-2007); o Electron Kinetics in Gas Mixtures Used for Analytical Glow Discharge Optical Emission Spectroscopy (GRICES 4 /OTKA 5 , M.J. Pinheiro, 2006-2007) o Mecanismos de Dissociação em Plasmas de H 2 , O 2 e Misturas com Ar, Utilizados na Modificação e Depósito de Materiais, (GRICES/CSIC 6 , L.L. Alves, 2006-2007); o Desarrollo y Optimización de Métodos Basados en Plasmas de Microondas para la Destrucción de Compuesto BETX y Derivados (MEC 7 (Spain), L.L. Alves, 2004-2007). o Sistema innovador de micro-ondas para a produção de mini-plasmas à pressão atmosférica (GRICES/CNRS 8 , L.L. Alves, 2007-2008). 1 Including the collaborations with the Associations EURATOM/IPP.CR and EURATOM/ENEA, IPP-Greisfwald and Brazilian Fusion Institutions. 2 The funding institutions, the main investigator and the duration is indicated between brackets. 3 FCT means “Fundação para a Ciência e a Tecnologia”. 4 GRICES means “Gabinete de Relações Internacionais da Ciência e do Ensino Superior”. 5 OTKA means “Hungarian Scientific Research Fund”. 6 CSIC means “Consejo Superior de Investigaciones Científicas”. 7 MEC means “Ministerio de Educación y Ciencia”. 8 CNRS means “Centro National pour la Recherche Scientifique”. 3 Project Responsible Person(s) Collaborating Institutions Portuguese Other Tokamak ISTTOK Horácio Fernandes Carlos Silva CFN 9 UBI 10 CEI 11 , CFA 12 CIEMAT 13 , IPP- Kharkov 14 , UI 15 , IFUR 16 , IFUSP 17 Participation in the collective use of the JET Facilities by the EFDA Associates Fernando Serra CFN, CEI, UBI EFDA 18 CSU 19 Culham UKAEA 20 Participation in the ASDEX Upgrade programme Maria Emília Manso Fernando Serra CFN IPP-Garching 21 Participation in the ITER Project Carlos Varandas Maria Emília Manso CFN EFDA CSU Garching Participation in the TJ-II programme Carlos Varandas CFN, CEI CIEMAT Maria Emília Manso Participation in the TCV programme Carlos Varandas CFN CRPP 22 Collaboration with the Association EURATOM/CEA J. Pedro Bizarro CFN Other studies on theory and modelling Fernando Serra CFN IFP 23 , PT 24 , DFRC 25 J. Pedro Bizarro Keep-in-touch activities on inertial fusion energy J.T. Mendonça CFP 26 Participation in the Fusion Technology Programme E. Alves ITN 27 , CFN Other fusion related activities Table 1.1 – Responsible person(s) and collaborating Institutions in the 2007 projects of the Association EURATOM/IST 9 CFN means “Centro de Fusão Nuclear” 10 UBI means “Universidade da Beira Interior” 11 CEI means “Centro de Electrónica e Instrumentação da Faculdade de Ciências e Tecnologia da Universidade de Coimbra” 12 CFA means “Centro de Física Atómica da Universidade de Lisboa” 13 CIEMAT means “Centro de Investigaciones Energeticas Medioambientales y Tecnologicas” 14 IPP- Kharkov means “Institute of Plasma Physics of the National Science Center” “Kharkov Institute of Physics & Technology”. 15 UI means “University of Innsbruck”. 16 IFUR means “Institute of Physics of the University of Riga” 17 IFUSP means “Instituto de Física da Universidade de São Paulo” 18 EFDA means “European Fusion Development Agreement” 19 CSU means “Close Support Unit” 20 UKAEA means “United Kingdon Atomic Energy Authority” 21 IPP-Garching means “Max-Planck-Institut für PlasmaPhysik” 22 CRPP means “entre de Recherches en Physique des Plasmas de École Polytechnique Fédérale de Lausanne” 23 IFP means “Istituto di Física del Plasma” 24 PT means “Politécnico di Turino” 25 DFRC means “Department de Recherches sur la Fusion Controlée”. 26 CFP means “Centro de Física dos Plasmas” 27 ITN means “Instituto Tecnológico e Nuclear” 11 Figure 2.12 - Effect of a frequency mismatch on the estimated amplitude of an AM signal. Offset in the mean estimated amplitude increases with measurement covariance R and mismatch πω∆ 2/ (a). The time evolution of the estimated amplitude (in grey) for the case R=1 and 100Hz mismatch is shown (b). Measurements of the modes’ phase indicate that they propagate in the electron diamagnetic direction. The mode, in principle a resistive tearing mode (linear growth rate of the order 1-2 ms), appears in bursts of ~0.1-0.5 ms time duration. An example of a (2,1) mode, destabilized by negative electrode biasing is shown in Figure 2.13. Only mode numbers for which the calculated coherency is above 66% are shown. Figure 2.13 - Poloidal mode number of coherent rotating magnetic fluctuations and mode frequency evolution (highlighted in grey) using Hilbert Huang Transform. 2.5.2 Poloidal structure of the ISTTOK edge fluctuations The poloidal structure of the fluctuations has been investigated using a poloidal array of Langmuir probes consisting of 7 pins poloidally separated by 1.5 mm. It has been observed that the ISTTOK edge plasma is characterized by low frequency (<100 kHz), small wavenumber (k θ < 3 cm -1 ) fluctuations. Large poloidal structures are clearly visible in the probe signal having a poloidal velocity around 1-2 km/s, a correlation length around 10 mm and a typical duration of 10 µs, resulting in an estimated structure poloidal size of 1-2 cm. The cross-correlation between the signals from different pins has also been investigated as a function of the frequency. It was observed that the correlation length is very large for frequencies between 50 and 150 kHz (>10 mm), being the correlation roughly constant across the 7 pins in this range (Figure 2.14). This frequency range corresponds to time scales of ~10 µs, which is the typical time scale of the large events observed. On the contrary, the correlation length is small at high frequencies. These results show evidence of multi-scale structures with different properties. The high frequencies are dominated by small-scale structures while the intermediate frequencies are dominated by large structures with long correlation lengths. Figure 2.14 - Poloidal cross-spectrum of the edge floating potential fluctuations. 2.5.3. Study of AC discharges The development of a new plasma position controller and digital controlled current amplifiers in 2006 has enabled to achieve regular AC discharges (end of 2007) with 250 ms, extending the plasma duration for almost one order of magnitude. The optimization of the machine space parameters allowed a successfully AC campaign during the IAEA Joint Experiment (see next section), generating a significant amount of relevant data to be analyzed during 2008. 0 2 4 6 Poloidal distance (mm) 0 100 200 300 400 500 Frequency (kHz) 12 2.6. ORGANIZATION OF THE ISTTOK JOINT EXPERIMENT CFN has organized in October 2007 the Host Laboratory Experiment on the tokamak ISTTOK. The Joint Experiment (JE) was organized in cooperation with the IAEA in the framework of the IAEA Coordinated Research Project (CRP) on “Joint Research Using Small Tokamaks” with the participation of 24 scientists from 13 countries (Austria (1), Belgium (1), Brasil (3), Bulgaria (1), Canada (1), Czech Republic (1), Egypt (1), Iran (2), Kazakhstan (1), Mexico(4), Poland (1), Russia (5), UK (1)). Taking into account the ISTTOK scientific programme and the feedback from the pre-registered participants the following areas were explored during the ISTTOK JE: (i) study of the poloidal structure of the edge fluctuations; (ii) tokamak operation in alternating current regimes; and (iii) testing of the liquid metal limiter concept. These activities were successfully carried out being distributed in five experimental sessions. Other areas related with plasma engineering and diagnostics were also investigated, although with no dedicated experimental sessions attributed. These areas, organized in small workshops, included: (i) plasma diagnostics; (ii) plasma control; (iii) data acquisition; and (iv) remote data access. Remote experimental sessions in the following weeks were also organized to complement the experiments performed during the ISTTOK JE. The participants could run experiments using the ISTTOK remote participation tools. Working groups have been formed for data analysis and remote meeting regularly organized to plan experiments and discuss results. Transverse areas to the ISTTOK JE were data acquisition, signal processing and remote access tools, where CFN has a long experience. These systems have been successfully used for data management on several tokamaks and they may serve as a platform for a unified environment for data exchange and processing in the framework of the activity on small tokamaks. 13 3. PARTICIPATION IN THE COLLECTIVE USE OF THE JET FACILITIES BY THE EFDA ASSOCIATES 1 F. Serra (Head), J.P. Bizarro, D. Borba, R. Coelho, S. Cortes, L. Cupido, L. Fattorini, A. Figueiredo, A. Fonseca, B. Gonçalves, S. Hacquin, M.E. Manso, F. Nabais, M.F. Nave, I. Nedzelski, I. Nunes, V. Plyusnin, T. Ribeiro, F. Salzedas, C. Silva, J. Sousa, A. Vannucci, C. Varandas, P. Varela, D. Alves, P. Belo, N. Cruz, J. Ferreira, L. Meneses. 3.1. INTRODUCTION The Association EURATOM/IST has continued its participation in the collective use of the JET facilities, in the frame of EFDA through the “JET Operation Contract” and the “JET Implementing Agreement”. The main activities in this project were related with: • Operation; • Scientific exploitation; • Performance enhancements; • Management. 3.2. OPERATION Two members of the IST/CFN staff have been working in the JET Operation Team:  One physicist has continued to work in the JET “Plasma Operation Group”, as a session leader for the Campaigns, and has also been involved on JET-EP2 ITER-like wall project;  One physicist has carried on his work in the Reflectometry and LIDAR Diagnostic Group, being responsible by: (i) maintenance of the X-mode correlation reflectometer (KG8b); (ii) the analysis and validation of the signals of the KG8b X-mode correlation reflectometer and the KG3 O- mode fluctuation reflectometer. 3.3. SCIENTIFIC EXPLOITATION 3.3.1. Introduction IST has proceeded with an important contribution to the JET scientific exploitation mainly through an active participation of sixteen scientists in the experimental campaigns (C18- C19) and in analysis/interpretation and modelling of the experimental data, with emphasis in the integration of transport and MHD codes. 3.3.2. Controlling the ITB oscillations in advanced tokamak scenarios with a dominant fraction of bootstrap current 2 Modelling of advanced tokamak scenarios with very large bootstrap current has continued, and a detailed understanding of the mechanism behind ITB oscillations, as well as of the means to control them, has been achieved. The analysis of truly steady-state tokamak discharges, meaning zero loop voltage, has also begun. Typical ITB oscillations in JET-like plasmas are shown in Figure 3.1. It was shown that relaxation oscillations associated with repetitive ITB buildup and collapse, with ICRH, NBI and LHCD, and with a dominant fraction of bootstrap current, can be overcome if the LHCD power is sufficiently high. This result has been obtained using a bench marked, fully predictive transport model iterated with given ICRH profiles and self-consistently with NBI and LHCD modules, the stabilizing role of the E×B flow shear being combined with that of reversed magnetic shear in the simulation of ITB dynamics. Figure 3.1 - Time evolution of the profiles for the Lower Hybrid (LH)- and Bootstrap (BS)-driven current densities, and for the plasma pressure. Also shown is the time evolution of the locations for the LH and BS current-density peaks and for the ITB foot. 3.3.3. Experiments on fast ion redistribution and losses Fast ion losses are of concern for ITER since the first wall can only tolerate losses at a very low level before suffering damage. To explore the physics of fast ion loss, JET has installed new fast ion loss detectors 3 and is now able to undertake dedicated fast ion redistribution experiments which allow predictions for ITER to be made. 1 Activities carried out in the frame of the Contract of Association EURATOM/IST and the Contract of Associated Laboratory, by CFN staff of the Experimental Physics, Microwave Diagnostics, Theory and Modelling and Control and Data Acquisition Groups. 2 Work performed in collaboration with CEA and VTT. 3 Particle loss signatures during sawtooth events at JET , M. Reich et al., 34 th EPS Conf on Plasma Physics, Warsaw, Poland, 2007 14 A set of experiments on fast ions redistribution was planned and carried out in 2007 experimental campaign. Using a high ICRH power on a low density plasma, a large population of highly energetic ions was build up which constituted a strong drive for many instabilities responsible for the redistribution of fast ions. In particular, diamagnetic, hybrid and precessional drift fishbones were destabilised, as well as TAE and core-localised TAE (tornado modes). Two types of fast ions were identified by the gamma-ray diagnostics 4 : fast protons with an energetic tail in excess of 4.5 MeV due to ICRH tuned to a fundamental H-resonance in the centre of the plasmas and D-ions accelerated with second harmonic heating whose energies exceeded 0.5 MeV. Aside of it, three types of losses were identified (Figure 3.2), one associated with sawtooth crashes, one associated with TAE and high frequency fishbones and a third group observed when tornado modes and low frequency fishbones are unstable. An important result came out from these experiments: The type and number of lost ions change as soon as tornado modes are destabilized. This may support the possibility of sawtooth crashes being caused by fast ions redistribution due to tornado modes. 3.3.4. Momentum transport modelling 5 Activities supporting interpretative and predictive transport modelling have been continued. Perturbative methods were used to complement the usual steady-state analysis with the aim of better understanding transport phenomena in fusion plasmas. Recently, in JET, experiments with modulation of the injected neutral beam power were accomplished, and, as believed, a modulated source of momentum was obtained 6 . Applying cross correlation methods to experimental data from the new improved Charge eXchange Recombination Spectroscopy (CXRS), particularly, toroidal rotation and ion temperature measurements every 10 ms, and to results from careful transport modelling with JETTO and TRANSP codes, interesting findings were obtained 7 . First results show that beam modulation technique can be useful for momentum transport studies and point to the existence of a “pinch” in the momentum transport, supporting on-going theoretical work done by collaborators 8 . 3.3.5. Effect of the deuterium density profile on the impurity transport Experiments at JET have found that impurity density profiles in the plasma core are dependent of the inclusion or not of ICRH. The impurity profile is hollow with ICRH and peaked when only NBI is in use. Two hypotheses were raised to explain these profiles: The impurity transport in the plasma core follows the neo-classical description or there is an anomalous contribution for the convective impurity velocity that is outward directed without the ICRH and inward directed otherwise 9 . Figure 3.2 - The three types of measured fast ion losses as function of the pitch angle and gyro radius: before tornado modes are destabilized (top), after tornado modes are destabilized (middle) and during a giant sawtooth crash (bottom) (pulse #66380). 4 V.G. Kiptily et al. Nucl. Fusion 42, 999, (2002). 5 Work performed in collaboration with CNR, VTT, IPP, Univ.Warwick, VR and UKAEA. 6 J.S. Ferreira, et al., Recent modeling of NBI modulation experiments, EFDA-JET Task Force T Meeting, Culham, UK, 29 March 2007. 7 P. Mantica et al., Analysis and modelling of NBI modulation session, EFDA-JET Task Force T Meeting, Culham, UK, 16 October 2007. 8 A. G. Peeters, et al., Toroidal Momentum Pinch Velocity due to the Coriolis Drift Effect on Small Scale Instabilities in a Toroidal Plasma, Physical Review Letters 98: 265003, June, 2007. 9 L.Carraro, Proceedings of 34 th EPS Conference, Warsaw July 2007. a) b) c) 15 Three sets of JETTO/SANCO simulations were done with the three different electron density profiles represented in Figure 3.3, with the same electron and ion temperature profiles. The electron density profiles changes are within the experimental error bar which is around 20%. The impurities were predictive in these simulations and an ad-hoc anomalous transport for ρ > 0.4 and completely neoclassical for ρ < 0.4, as represented in Figure 3.4, was used. This transport profile is very similar to the ones observed experimentally 10 . In steady state regime the impurity profile is observed to be hollow when a flat density profile is used in the simulations and peaked when a peaked density profile is used within the region where the transport is completely neoclassical. The neoclassical convective impurity velocity is inward for the peaked profile and outward for flat profile case. The neo-classical transport seems to explain the hollow profiles observed experimentally. However, further simulations using more theoretical driven impurity anomalous transport should be performed to confirm these results. n T T Figure 3.3 - Density and Temperature profiles used in JETTO/SANCO simulations. D imp V neo n imp Figure 3.4 - Sum of all ionization stages density profiles, impurity diffusion and neo-classical convective velocity. The colour of the impurity profiles corresponds to the colour of the deuterium profiles in Figure 3.3. 3.3.6. Synergetic effects on impurity transport with Deuterium SOL flows JET impurity seeded plasma experiments have at least two impurities present. The introduced extrinsic impurity (normally Nitrogen, Neon and/or Argon) coexists with intrinsic Carbon which comes from the wall and divertor plates due to the chemical and physical sputtering. An increase of the friction force on the recycled impurity due to the presence of Carbon was observed in previous simulations with EDGE2D/NIMBUS 11 . The simulations using EDGE2D/NIMBUS allowed concluding that the addition of an intrinsic impurity (Carbon) does not qualitatively change the screening of the extrinsic impurity (Neon) by the main gas puffing (Figure 3.5). This means that friction force and thermal force still play dominant roles in establishing the Neon distribution. The introduction of a second impurity increases total radiated power resulting in a decrease in electron temperature, moving the conditions for plasma detachment to a lower density range. A significant reduction of the C 2+ spectral line intensity and Z eff not increasing significantly was observed experimentally after the onset of extrinsic impurity puff in high density and triangularity JET H- mode plasma. These findings inferred a conclusion that Carbon was replaced by the extrinsic impurity in the plasma core 12 . Although simulations with EDGE2D/NIMBUS gave similar results for high density plasmas was not possible to draw the same conclusion, because Carbon was not substituted by Neon in the plasma core but in the divertor region. The increase of the Zeff is mainly due to an increase of the Carbon concentration in the core rather than the Neon concentration which was very low. The increase of the Carbon concentration was also observed in the reference JET pulses used in the EDGE2D/NIMBUS simulations, (Figure 3.6), after the onset of Argon puff: 53550 (Argon seeded plasma); while there was change in the pulse 53549, which was no seeded plasma. The reduction of the C 2+ spectral line intensity was not due to a decrease of Carbon influx from the divertor plates but an increase of Carbon upstream flux, leading to a decrease of Carbon flux to the pump. Overall the addition of an extrinsic impurity, or second impurity into the plasma, changes the parallel transport of the intrinsic impurity, or first impurity, by decreasing the friction force on it. As a result the second impurity does not allow the first impurity to be removed from the plasma through the pumps and even pushing it further into the plasma core, while the first impurity has exactly the opposite effect on the second impurity. 3.3.7. Effects of the magnetic configuration on the impurity transport and plasma detachment The divertor configuration at JET was changed allowing more flexibility on the magnetic equilibrium configuration. Figure 3.7 shows the four possible 10 Giroud, C., et al, Proceedings of 34 th EPS Conference, Warsaw July 2007. 11 Fichtmuller, M., et al, J. Nuclear Mat., 266-269 (1999) 330. 12 Monier - Garbet, P., et al , Nuclear Fusion , 38 (1998) 1839. 16 0.0 2.0 4.0 6.0 8.0 10.0 12.0 14.0 0.00 0.50 1.00 1.50 2.00 Deuterium Puff Rate (*1.0e22 s-1) Carbon Concentration (%) Carbon Neon+Carbon Figure 3.5 - Carbon concentration inside the last closed flux surface as a function of deuterium puff rate for the EDGE2D/NIMBUS simulations with Carbon only (pink line) and simulation with Neon (orange line). Figure 3.6 - Carbon concentration profiles for three different times at 59.5 s, half a second before the impurity puff onset, at 60.5 s, half second after the impurity puff onset and at 62.5 s, 1.5 s after the onset and half a second after the onset of the exponential rise of the impurity radiations. The profiles are from two the JET pulses one is the reference pulse without extrinsic impurity 53549 (black line) and with the extrinsic impurity 53550 (red line). configurations used in the study of the effects of the magnetic configuration on the impurity transport and plasma detachment. An external source of momentum was also included. The EDGE2D/NIMBUS simulations show that all configurations that have the strike point at tile 5 have higher deuterium densities at the separatrix at outer mid plane. In these configurations the plasma is detached at the inner target even for deuterium puff rates as low as 1×10 20 particles/s due to lower pump efficiency (Figure 3.8). Nevertheless a lower concentration of impurities in the plasma core was observed. 3.3.8. Testing mechanisms to explain the parallel transport in the SOL Simulations were done to compare JET plasmas with the new ITER like configuration (AT) with the external momentum force and the usual high triangularity magnetic equilibrium configuration (HT3). The relevant experimental values were used: inlet deuterium gas puff positioned at the outer mid plane separatrix varying from 3.5x10 21 particles/s until the pressure at the targets was less than a half of the pressure at the outer mid plane; the power across the separatrix was P ions =6.0 MW and P elec. =6.0 MW; the impurity content was set to be constant, 5.0x10 17 particles in the whole computational grid; and the perpendicular transport was determine using the JETTO/SANCO simulations for this pulse, 70286 in ELM free H-mode. Figure 3.7 - Four possible magnetic equilibrium flux surfaces at the divertor region for the latest divertor configuration: a) low triangularity with the X point at the middle of the divertor region, the strike point at tile 7(66515); b) high triangularity with the X point at the middle of the divertor(53549); d) high triangularity with the strike point at tile 5 and the X point closer to the inner target (15 cm) (66296) and d) high triangularity with the X point closest to the inner target (5 cm) (70286). 17 1.00 2.00 3.00 4.00 5.00 6.00 7.00 8.00 9.00 0.00 0.50 1.00 1.50 2.00 2.50 Deuterium Puff Rate (*1e22 s-1) ni(a) (*1019 m-3) 53549 66515 70286 66296 Figure 3.8 - Deuterium density at the separatrix increases as a function of the deuterium puff rate for the different magnetic configurations. Figure 3.9 shows the simulation results for the normalised total pressure at the inner (a) and outer (b) targets to the outer mid plane total pressure of all possible combinations for the parallel transport. The plasma detachment occurs when the normalised pressure at the targets drops below 0.5. From the figure it is clear that the maximum gas puff rate possible is 7.5x10 21 particles/s which is much lower than experimentally observed for this type of magnetic equilibrium. For some of the cases, mainly with the flux limiters, the plasma detachment occur first at the outer target like or even in both targets at the same time. This also occurs for the case with the ballooning transport and the external source of momentum. 0 0.5 1 1.5 2 2.5 2 4 6 8 10 gas puff (*1e21 s-1) Pinner/Pmid baseline balloning heat flux limiters baseline heat flux limiters balloning force baseline force balloning force heat flux limiters baseline force heat flux limiters balloning threshold 0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 2 4 6 8 10 gas puff (*1e21 s-1) Pouter/Pmid baseline balloning heat flux limiters baseline heat flux limiters balloning force baseline force balloning force heat flux limiters baseline force heat flux limiters balloning threshold Figure 3.9 - Normalised total pressure at the outer (a) and inner (b) targets by the total pressure at the outer mid plane separatrix for all the possible combinations of the parallel transport in the plasma EDGE2D/NIMBUS. Simulations with the external source of momentum predict a much higher deuterium density at the outer mid plane separatrix than for all the cases without the force the deuterium density. In latter cases the deuterium density are within the error bar of the experimental measurement. Besides all the simulations with the different parallel transport contributions predict a much higher increase of the deuterium density with the deuterium gas puff than it is experimentally observed. 3.3.9. Influence of the ELMs in the impurity transport Figure 3.10 shows the time traces of the Neon concentration inside the separatrix for an ELMy H-mode plasma for the three different deuterium gas puff levels which are compared with the correspondent runs without the ELMs. The Neon concentration inside separatrix is lower for the simulations where ELMs were included. Qualitatively this result is independent on the deuterium puff rate. The reason for fewer impurities in the plasma core for the ELMy H-mode in COCONUT (when compared with results from stand-alone JETTO/SANCO code 13 ) and possibly in real experiments, is the fact that ELMs not only removes deuterium particles and energy from the ELM perturbation region inside separatrix but also from the main SOL to the wall and divertor target plates. The high deuterium flux to the divertor during the ELM drags the Neon particles also to the divertor region through the parallel friction force. While the energy is deposited and lost at the walls and divertor target plates the ionised impurity particles in the divertor region are not lost and return back to the main SOL. The time scale for the Neon particles going upstream is longer than the time scale of the atomic processes. A great number of Neon particles become neutralised and removed from the system through the cryogenic pump. Consequently there are fewer impurities in the whole plasma than in the ELM free H-mode plasmas. It is important to note that although the ELMs have a positive effect on the impurity removal, it only delays the radiative collapse in H-mode plasma with low deuterium puff rate. 0.3 0.2 0.1 021.07 21.1221.02 Neon concentration (%) (1021) Time (s) JG07.406-8c 1.0e21 p/s 5.0e21 p/s 9.0e21 p/s Figure 3.10 - Time evolution of the total Neon density inside the last closed flux surface for two deuterium puff rates of: a) 1 × 10 21 p/s and b) 9 × 10 21 p/s and with Neon puff rate of 6 × 10 19 p/s. 13 Belo, P. et al, Plasma Phys. Control. Fusion, 46 (2004) 1299. 18 3.3.10. Influence of the impurity concentration in the plasma core on the ELM frequency It has been observed experimentally at JET that the ELM frequency decreases with the radiation levels for high triangularity and high density plasmas. To simulate this effect two sets of COCONUT simulations were done, using two different levels of impurity puff rate and for each set two runs with deuterium puff rates of 1×10 21 particles/s and 9×10 21 particles/s. The starting point of these COCONUT simulations was the end of the simulations previously described which were evolved for another 200 ms. In the first set the impurity puff rate was not changed while in the second set the Neon puff rate was increased from 6×10 19 particles/s to 3×10 20 particles/s. The deuterium flux across the last closed flux surface for these simulations are plotted in Figure 3.11a. This figure shows a clear decrease of the ELM frequency with the Neon puff rate. This figure also shows that the ELM frequency is the lowest for the highest deuterium and impurity puff rate, as observed in the experiment. Figure 3.11b shows clearly that the simulation with the highest radiated power within the ETB had the lowest ELM frequency. This simulation corresponds to the case with highest deuterium puff rate and the highest Neon puff rate. 2 1 4 (a) Dpuff = 1.0e21 p/s Nepuff = 6.0e19 p/s Dpuff = 1.0e21 p/s Nepuff = 3.0e20 p/s 3 021.22 21.26 21.30 21.34 (x1023) (s - 1) Time (s) JG07.406-10a 2 1 5 (b) Dpuff = 9.0e21 p/s Nepuff = 6.0e19 p/s Dpuff = 9.0e21 p/s Nepuff = 3.0e20 p/s 3 021.22 21.26 21.30 21.34 (x1023) (s - 1) Time (s) JG07.406-10b 4 Figure 3.11 - Main ion flux through the last closed flux surface for two sets of runs with different Neon inlet level of 6 × 10 19 p/s and 3 × 10 20 p/s and with different deuterium puff rates of: a) 1 × 10 21 p/s and b) 9 × 10 21 p/s. 3.3.11. Fixed frequency and correlation reflectomer (KG8b) data analysis Using the JET reflectometry fixed frequency systems coherent modes inside of the plasma column were detected. Figure 3.12 shows the identification of Alfvén Cascades (ACs) and Toroidal Alfvén Eigenmodes (TAEs) from the spectrograms of the phase perturbation in one of the fixed frequency channels (103 GHz) of KG8b reflectometer system. Figure 3.12 - Alfvén Cascades and Toroidal Alfvén Eigenmodes identified in the spectrogram of phase perturbation of the KG8b reflectometer 1 (channel 103 GHz). Figure 3.13 permits to identify the Fishbone instability in the spectrogram of KG8b reflectometer (channel 85 GHz). Figure 3.13 - Fishbone instability identified in the spectrogram of signal of the KG8b reflectometer (channel 103 GHz). Figure 3.14 presents a spectrogram where is possible to identify the bi-TAEs from the signal of KG8b reflectometer (channel 62 GHz). The Fishbone instability and Bi-directional TAEs have a lack of localization information and KG8b could give interesting information about that (like was recently obtained in the characterization of the ACs and TAEs). The effect of the Lower hybrid Current Drive (LHCD) and low magnetic shear at large radii in transport barriers at high betaN of JET was observed in the KG8b reflectometry. 19 Figure 3.14 - Bi-directional TAEs identified in the spectrogram of signal of the KG8b reflectometer (channel 92 GHz). 3.3.12. Turbulence studies from radial correlation reflectometry in JET 14 Radial correlation reflectometry can be used to estimate the radial scale of turbulence L from the variation of coherence with the radial separation between the cutoff positions of two distinct probing waves. JET correlation reflectometry diagnostic has four reflectometer systems, each one equipped with a fixed-frequency channel and a variablefrequency one, allowing measurements around four different radial positions. The formation of an ITB is accompanied by a reduction of the core turbulence, and a decrease of the turbulence correlation length in the region inside the ITB foot 15 . During JET pulse #69389, an ITB is formed between R = 3.49 m and R = 3.54 m. Figures 3.15 and 3.16 show the analysis of data collected by two reflectometer systems with fixed channels working at 103 GHz and 92 GHz, respectively, in two different measurements during this pulse. While the first measurement occurs before the ITB, the second one takes place during the ITB. For the 103 GHz system, which scans the region inside the ITB foot from R ≈ 3.42 m to R ≈ 3.535 m, a reduction from L = 1.14 cm to L = 0.43 cm can be observed between the two measurements, which might be associated with a reduction of the core turbulence. On the contrary, the cutoff positions of the 92 GHz system are located in the outboard region of the ITB from R ≈ 3.68 m to R ≈ 3.815 m, where no significant change occurs in the measured correlation length. In this case, the low L ≈ 1 mm values are consistent with higher turbulence levels, for which the coherent reflected power is low and the measured correlation length can be much smaller than the real one 16 . These results show a clear decrease of the radial correlation length in the region inside the ITB foot, which is compatible with a reduction of turbulence in the plasma core. The correlation length in the region outboard of the ITB remained unchanged by the ITB, which is consistent with the conclusion that turbulence in this region is unaffected by the formation of the ITB. These measurements point to correlation lengths with an order of magnitude of 1 cm in the plasma core of JET plasmas without ITBs, and half that value when ITBs are formed. More conclusive and quantitative results require theoretical and code modelling, which are essential to validate correlation reflectometry results. -2.0 -1.5 -1.0 -0.5 0.0 0.5 1.0 1.5 2.0 3.44 3.46 3.48 3.50 0.0 0.2 0.4 0.6 0.8 1.0 Before ITB L = 1.14 cm Cutoff Position (m) ∆ R (cm) (a) γ L = 1.14 cm 0.0 0.2 0.4 0.6 0.8 1.0 After ITB Cutoff Position (m) γ L = 0.43 cm -2.0 -1.5 -1.0 -0.5 0.0 0.5 1.0 1.5 2.0 3.51 3.52 3.53 (b) ∆R (cm) Figure 3.15 - Coherence analysis using reflectometer system 4 working at 103 GHz fixed frequency, showing a reduction of the correlation length L in the region inside the ITB foot. The first measurement (a) occurs before and the second (b) during the ITB. 0.0 0.2 0.4 0.6 0.8 1.0 3.68 3.70 3.72 3.74 3.76 0.0 0.2 0.4 0.6 0.8 1.0 Before ITB γ Cutoff Position (m) ∆ R (cm) (a) γ L = 0.14 cm 0.0 0.2 0.4 0.6 0.8 1.0 After ITB Cutoff Position (m) γ L = 0.13 cm 0.0 0.2 0.4 0.6 0.8 1.0 3.78 3.79 3.80 3.81 (b) ∆ R (cm) Figure 3.16 - Coherence analysis using reflectometer system 3 working at 92 GHz fixed frequency, showing no significant change in the correlation length L in the region outboard of the ITB. The first measurement (a) occurs before and the second (b) during the ITB. 14 Work performed in collaboration with CEA, UKAEA and PPPL. 15 G. D. Conway et al., Phys. Rev. Lett. 84, 1463 (2000). 16 G. Leclert et al., Plasma Phys. Control. Fusion 48 , 1389 (2006) . 20 3.3.13. Sweeping frequency reflectometer (KG8a) The KG8a reflectometry system is proof of principle diagnostic with one channel only aiming to demonstrate the capability of reflectometry to measure density profiles using complex and long transmission lines such as those implemented at the JET tokamak. After first experiments some problems of long propagation paths were revealed. Some modifications were made to ameliorate performance, including the installation of a new delay line and a new frequency calibration. The data evaluation program for profile inversion was also upgraded with optimized filtering and updated calibration. Figure 3.17 presents the schematic configuration of system. During the last week of the 2007 campaign, high resolution density profiles from swept reflectometry were, for the first time, obtained at JET. In particular, the abrupt change of gradient due to ELMs could be detected. Figure 3.18 shows the edge density profiles from Reflectometry fitting the density data from Thomson scattering diagnostic in both L and H modes. After the promising results, JET decided to implement a swept reflectometry diagnostic with six channels. 3.3.14. Li Beam source characterization The characterization of lithium beam after installation of a new emitter was performed. The lithium beam characteristics investigated after installation of new emitter showed the same double (Li-Na) structure of the beam, as it was with a previous emitter. This result confirmed a suggestion of not a proper procedure of the emitter preparation. HV tests and step-by-step training allowed increase of beam energy from 45 keV to 65 keV, thus sufficiently improving the diagnostic capabilities. Analysis of the plasma density profiles de-convoluted with EFIT and EFTM equilibria showed approximately 1 cm inside shift of the profiles in high triangularity regimes in accordance with the shift of the magnetic surfaces. A review of solid state and plasma ion sources used in lithium beam diagnostic has been completed and presented, pursuing the aim to analyze different concepts and possibilities to increase the intensity of lithium beam. 3.3.15. Motional Stark Effect signal processing The Kalman filter has been proposed as an amplitude estimation method of known frequency components in quasi-periodic signals 17 (Figure 3.19). It was shown that it provides an improved filtering capability as well as the minimization of the Edge Localized Modes (ELMs) impact and 50 Hz power grid component when compared with the conventional lockin-amplifier signal processing for the Motional Stark Effect (MSE) diagnostic signals 18 . As a result, and aiming the implementation of an upgrade to the current real-time MSE system in JET, a C code has been developed for multi-component amplitude estimation of known frequencies in the MSE Avalanche Photo-Diode (APD) signals. Figure 3.17 - Schematic implementation of the KG8a reflectometer after the implementation of the delay line. 17 R. Coelho and D. Alves, “Real time Lock-in amplifier implementation using a Kalman filter for quasi-periodic signal processing in fusion plasma diagnostics”, submitted to IEEE Transaction on Plasma Science (2008). 18 R. Coelho, D. Alves and EFDA contributors, “Real-time Magnetic Field Pitch Angle Estimation with a Motional Stark Effect Diagnostic Using Kalman Filtering”, International Conference on Burning Plasma Diagnostics, Varenna, Italy September 24 – 28, 2007, to appear in AIP Proceedings. 27 4. PARTICIPATION IN THE ITER PROJECT 1 C.A.F. Varandas (Head), M.E. Manso (Deputy Head), L. Cupido, H. Fernandes, F. Serra, A. Silva, P. Varela, A. Ferreira, J. Santos 4.1. INTRODUCTION This project included in 2007 scientific work on microwave reflectometry, control and data acquisition and quality assurance, as well as activities for the promotion of ITER to the Portuguese firms and research units. 4.2. MICROWAVE REFLECTOMETRY 4.2.1. Introduction IST/CFN has carried out activities related with the conceptual study of the plasma position reflectometer and the development of a prototype of an advanced reflectometer. 4.2.2. Plasma position reflectometer A first draft of the Project Plan was submitted on November and the Project Plan status was presented in December, during a Project Pleaders Meeting (PLM) organized by EFDA. Currently, the Draft Project Plan is being revised according to the suggestions that arise from the PLM so that a new version can be submitted early 2008. The full cost of the procurement package, including resources, is being evaluated. The following subtasks were also performed by CFN in 2007:  Study of three possible solutions for the diagnostic localization;  Simulation of the routing of the oversized waveguides from the PIT cell to the diagnostic RF hall. 4.2.2.1. Electronics location The ex-vessel waveguide routing is closely related with the location of the mm-wave front-end and associated electronics. Three different possibilities are currently being envisaged: (i) all equipment in the pit cell (PC); (ii) all equipment in the Diagnostic Hall (DH) and/or Assembly/RF Hall (RFH); and (iii) the mm-wave front-end in the PC and the associated electronics in the DH/RFH. Each of the solutions for the mm-wave/electronics location discussed above presents advantages, disadvantages, and implementation problems. Therefore, we prefer to keep all options open deferring the choice of a particular solution to a later time when the designs are more advanced and/or more information about each location is available. Because it involves the largest number of interfaces with the tokamak building and its surroundings we started by routing the waveguides for the case where the mm-wave front-end and electronics are located away from the port cells, in the diagnostic hall and/or in the RF hall. To prevent and help to identify possible clashes with other diagnostics, the space occupied by the cubicles that would contain the mm-wave front-end and electronics has been modeled (by solid parallelepipeds) in CATIA. This has been done for all possible locations. Figure 4.1 shows the ex-vessel waveguide routing for gaps 4, 5 and 6. 4.2.2.2. Development of a solution for a frequency combiner/de-combiner Independently of the final choice for the electronics location, it is foreseen the use of three frequency bands (K, Ka, and U) to cover the desired frequency range (15 – 60 GHz). These bands must be combined in a single waveguide before being tapered to rectangular or circular waveguide. On the receiver side, a de-combiner should be used to separate the three bands. 4.2.2.3. Directional coupler solution Figures 4.2 and 4.3 show a three-band combiner that uses a multihole directional coupler and the corresponding decombiner setup. Testing of a four port multihole power splitter to combine the K and Ka bands into a single WR51 waveguide has led to excellent results. The coupling to each output port is 4.8 dB down in respect to the output port. Directivity is greater than 40 dB. Tests must now be done in the upper band 40 to 60 GHz to fully validate this solution. Figure 4.1 - Proposed ex-vessel waveguide routings for gaps 4, 5, and 6. 1 Activities carried out in the frame of the Contract of Association EURATOM/IST and the Contract of Associated Laboratory, by CFN staff of the Experimental Physics, Microwave Diagnostics and Control and Data Acquisition Groups. 28 Multihole directional coupler Model 19230 (Flann) 20×13 to WR51 taper K band generator WR51 to WR42 taper Ka band generator U band generator WR51 to WR19 taper WR51 to WR28taper Figure 4.2 - Combiner setup using a multihole directional coupler model 19230 from FLANN. Multihole directional coupler Model 19230 (Flann) 20×13 to WR51 taper K band mixer WR51 to WR42 taper Ka band mixer U band mixer WR51 to WR19 taper WR51 to WR28 taper Figure 4.3 - De-combiner setup using the same multihole directional coupler. 4.2.2.4. Design of a taper to simulate the coupling of the standard WR51 waveguide to the 20x12 mm waveguide The waves must be coupled to the non-standard waveguides installed inside the vessel by using a tapered transition from a standard waveguide band. Due to the minimal frequency of 15 GHz we propose to use the WR51 waveguide with internal dimensions of 6.48x13 mm. This almost matches the 12 mm of the in-vessel waveguide. Instead of designing a complicated taper with tapering in both dimensions we’ll make a proposal to increase the dimension of the in-vessel waveguide from 20x12 mm to 20x13 mm. This should not have big implications in the overall design besides a small increase of the antennas gain. Our approach was to design a linear taper with the size of 10 wavelengths for the minimal frequency. In the model used on HFSS (Figure 4.4.), two symmetry plans were used (perfect E and perfect H) to speed up the simulations by reducing the model size and consequently CPU and memory consumption. The taper performance was evaluated using HFSS and the results are presented in Figure 4.5, showing insertion losses below 0.06 db and return losses smaller than -38dB in the frequency range 15 to 60 GHz. The increase of the oscillations at high frequencies in the return loss curve is linked to simulation “noise”. Figure 4.4 - HFSS model used to simulate the electromagnetic performance of the WR51 to 20x13 mm taper. Two symmetry plans were used (perfect E and perfect H) to speed up the simulations by reducing the model size and consequently CPU and memory consumption. Figure 4.5 – Electromagnetic performance of the WR51 to 20x13 mm taper: attenuation (red trace) and return loss (blue trace). 4.2.2.5. Simulation of critical bends and their optimization using an electromagnetic code HFSS has been used to evaluate the electromagnetic performance of critical components of the in-vessel transmission lines, namely the so-called first bends which connect the emission/reception antennas to the waveguides. Two types of bends have been simulated: constant radius bend and hyperbolic secant bend. For the later, simulations were performed for two different values of the equivalent radius: 72 and 120 mm. Results show that the hyperbolic secant bends have better performance than constant radius bends. Results also show that the performance is better for smoother curves. 29 4.2.2.6. Simulations of broad band swept reflectometry experiments Reflectometry at ITER presents unusual challenges not faced in present day machines. Apart from the harsh environment surrounding the diagnostics, the need of oversized waveguides, which also has to act as antennas, their insertion within a gap in the blanket module and the proximity of the antennas to the very steep edge plasmas, create a strong potential for spurious mode excitation as well as for resonances and multi-reflections. In the case of GAP 5, the scenario is even more acute since the plasma will most likely not be probed perpendicularly to the isodensity surfaces. Those surfaces in addition exhibit a poloidal spatial divergence plus curvature, which are most adverse conditions for profile measurements. In a first approach simulations were performed not including the blanket, the curvature, MHD modes or turbulence. The results showed that the effect of the electronic density poloidal divergence can be tolerated except for extreme values of divergence that will seldom occur. First simulations including the blanket, however, indicate that that the blanket metallic structure induces a high level of multi-reflections. This study will be pursuit in 2008. Figure 4.6 - Electromagnetic field snap-shot showing a plasma with electronic density poloidal divergence being probed at 60 GHz. 4.2.3. Prototype of an advanced reflectometer The development of a new generation of swept reflectometers capable to cope with the long and complex transmission for JET and ITER was pursued. The studies and simulations for the generator section of a full coherent reflectometry system have been performed some laboratorial tests and partial prototypes were produced. The project underlying technique is now mature enough to be implemented in a diagnostic to be implemented at a large fusion machine. 4.3. CONTROL AND DATA ACQUISITION 4.3.1. Introduction The activities on control and data acquisition were in 2007 related with the conceptual design of dedicated systems for two ITER diagnostics, the equatorial visible/infra-red wide angle viewing system and the core-plasma LIDAR Thomson scattering system, and the participation in the European Ad-Hoc Group that is following the ITER CODAC activities. 4.3.2. ITER Equatorial Visible / IR Wide Angle Viewing system 2 The amount of data provided by the infra-red and visible cameras at ITER is expected to be considerably larger in respect to other diagnostics. ITER will have twelve infrared cameras plus twelve visible cameras in four different equatorial port plugs. One of the key functions of these cameras will be the protection of the first wall, thereby is considered a particular diagnostic where direct connections to the Central Interlock System are required. In 2007 CFN developed a full specification following the ITER CODAC guidelines. This specification, presented in three reports, covered the camera specifications, data collection and compression, image processing, internal state machine, communication with CODAC and a proposal for a prototype (Figure 4.7). Figure 4.7 - Block diagram of the PP11 CODAC sub-system. 2 Task TW6-TPDS-DIADES-PP11. 30 4.3.3. Core-plasma LIDAR The following tasks were performed in 2007 regarding the local CODAC sub-system design for the core-plasma LIDAR (Figure 4.8):  Contribution to the project plan of the data acquisition CODAC interfacing and local control systems for the ITER core-plasma LIDAR Thomson scattering diagnostic;  Elaboration of the Intermediate Report on the Interfaces and Control system of the ITER core-plasma LIDAR. 4.4. QUALITY ASSURANCE 3,4 IST is participating in the development of the (QA) system for the ITER EU domestic agency and implementation of a Quality Assurance Programme in the European Fusion Associations for ITER-relevant activities (contract FU06- CT-2006-00405) 5 . The main responsibilities of IST in this task were:  Report on the level 3 documentation. The initial set of Level 3 documents (typically standards and rules) have been identified, which can be used for the initial procurements. To facilitate the access, the documents were compiled in a MS Access database that is part of this deliverable;  Report on the implementation of quality provisions showing the practical application of the proposed principles of QA and the analysis of the problems encountered during the implementation. A draft quality management system for F4E has been prepared in order to comply with the ITER Quality Programme. CEA and IST have implemented quality provisions in two on going R&D EFDA tasks. In parallel, CFN has started the preliminary studies for the implementation of QA procedures in our own activities. Figure 4.8 - Interfaces and Control system of the ITER core-plasma LIDAR. 3 Task TW6-TDS-QA2. 4 Work in collaboration with “Instituto de Soldadura e Qualidade”. 5 Work in c ollaboration with the Association EURATOM/CEA. 31 5. PARTICIPATION IN THE ASDEX UPGRADE PROGRAMME 1 M.E. Manso (Head), F. Serra (Deputy Head), D. Borba, R. Coelho, L. Cupido, L. Fattorini, S. Hacquin, I. Nunes, T. Ribeiro, F. Salzedas, A. Silva, F. Silva, P. Varela, A. Combo, A. Ferreira, S. Graça, L. Guimarães, L. Meneses, J. Santos. 5.1. INTRODUCTION This project included in 2007 activities related with the development, modelling and scientific exploitation of microwave reflectometry system as well as plasma physics studies on transport and MHD. 5.2. MICROWAVE REFLECTOMETRY 5.2.1. Introduction The two hopping systems developed by CFN with improved sensitivity and enlarged measuring capability due to the frequency hopping set-up for each plasma discharge were fully operational in 2007. The swept FMCW profile reflectometer system, however, was not in operation during the 2007 campaign due to renovation of waveguides and the installation of isolation shutters for protection against ECHR radiation after the recent upgrades and modifications in the ECRH system. An alternative bistatic transmission line for the broadband reflectometry system has been investigated and design studies are in progress. A proposal for a new system has been performed and will be presented in 2008. In order to increase the capability of profiles from FM-CW systems, a new PCI data acquisition system is being developed. 5.2.2. Hardware developments 5.2.2.1. Microwave circuits and systems Protection switches for the electronics of the FM-CW diagnostic were installed except for the two channels Q and V bands operating in X mode. However, the critical invessel directional couplers cannot be protected and a new system must be considered to measure density profiles from swept reflectometry on ASDEX Upgrade. The outer and in vessel access for the implementation of a microwave broadband transmission line at a different location for a possible new FM CW reflectometry system using a bi-static arrangement (avoiding critical in-vessel components) was investigated. It was found that no possibility exist to implement a new system neither at the HFS or LFS. It was studied an inboard launch at the High Field Side at the same location of the present system that would permit to probe the plasma from the edge to the core operating in lower cutoff – X mode. This would in addition be an ITER relevant demonstration not possible to test in any other fusion device. The study of electromagnetic access is presented in Figure 5.1. Figure 5.1 - Study of the electromagnetic access of probing microwaves to the ASDEX Upgrade plasma using O and X mode waves from both the HFS and LFS. 1 Activities carried out in the frame of the Contract of Association EURATOM/IST and the Contract of Associated Laboratory, by CFN staff of the Microwave Diagnostics, Theory and Modelling and Control and Data Acquisition Groups, in collaboration with the ASDEX-Upgrade Team. Contact Person: G. Conway 32 5.2.2.2. Control and data acquisition A new PCI data acquisition system able to increase significantly the density profile measuring capability of the FM-CW system is being developed. A 2-channel Transient Recorder prototype was developed, constructed and tested. The control software structure and development tools were assessed and specified. The development of the DSP software, PCI Waveform Generator and its firmware were initiated. 5.2.3. Data analysis 5.2.3.1. Density profiles Software development has proceeded with new algorithms for the automatic analysis of the edge pedestal characteristics directly from the group delay. An investigation of magnetic ripple effects on the inversion of X-mode data will be used to improve the density profile reconstruction accuracy, in particular at the plasma outer edge and SOL. It was initiated the study of a new density profile inversion technique using algorithms based on Bayesian analysis 2 . 5.2.3.2 Real time density profiles Validation studies of the real-time reconstruction procedure for fast plasma position monitoring using neural networks were completed. Using a highly optimized code on a dual core 2 GHz Intel CPU the separatrix position in ELMy H- mode discharges could be tracked with a <1 cm resolution and a 10 ms repetition, thus meeting the ITER requirements. A demonstration of a real-time radial position control system is planned for the 2008 campaign using a fast dedicated acquisition system. At the moment several configurations using in-house available/developed technologies (both at IPP and CFN) are under consideration. An highly optimized multithreaded calculation code was implemented to reconstruct the profiles from the binary acquired samples up to the final profile. This code was benchmarked in a dual core 2 GHz Intel CPU. The inversion of a density profile (up to n e =3x10 19 m -3 ) using data from bands K, Ka and Q, acquired in a burst of four sweeps taken every 35 us, took < 400 µs (Figure 5.2). With the use of faster quad-core processors ~200-250 µs profile reconstruction cycles are expected to be achieved using the four probing bands K, Ka, Q and V (profiles up to ne=6x10 19 m -3 ) and 4 sweep/burst measurements. This code was tested using AUG experimental data showing good separatrix position tracking capabilities, as had been achieved and demonstrated in the referred studies using the standard supervised methods. Figure 5.2 - Positions error histograms of the reconstruction of a test dataset perturbed by an high amplitude level of density fluctuations (9% of n e_sep ) with a NN and the Abel inversion with various initializations (limiter = standard / experimental initialization). 5.2.3.3. Upgrade of the reflectometer acquisition system to real-time capability The demonstration of the application of reflectometry for control purposes in AUG requires the adaptation of the existing diagnostic. This upgrade will make the system compatible with an integration in the real-time (RT) AUG diagnostic network. At the same time, it must have a minimal impact in the present diagnostic operation and configuration. Since dedicated acquisition systems are required to achieve real-time compatible on-line data transfer rates to the data processing host, a new such system needs to be built. At the moment several configurations using in-house available/developed technologies (at IPP and CFN) are under consideration. A fast data acquisition front-end needs to be developed to be connected to the processing host using an optical link connection based either on Hot-Link/cPCIe (IPP), depicted in Figure 5.3, or RocketIO/ATCA (CFN) technologies. In any case, the data collecting board should provide very fast data transfer speeds to the main memory of the data processing host. A standard dual quad-core workstation/server, featuring PCIe slots (4x, 8x) and running a RT Linux variant, is thought to be adequate to produce the target measurements in a theoretical 1 ms cycle. The ultimate goal is to produce HFS and LFS edge density profiles in the fastest AUG RT cycle (1.6 ms 3 , possibly 1 ms 4 ), which would make the measurements compatible with the plasma performance feedback control timing, and would allow multiple profile measurements to be made on the timescale of the magnetic feedback control for plasma vertical and radial position (10 ms) and plasma shape (100 ms) 5 . 2 Work in collaboration with Dr. Rainer Fisher (IPP). 3 G. Raupp et al., Fusion Eng. Design 81, 1747 (2006). 4 W. Treutterer, 6th IAEA TM on Control Data Acquisition and Remote Participation on Fusion Research, 2007, Japan. 5 G. Raupp et al., Fusion Eng. Design 74, 697 (2005). 33 Figure 5.3 - Simplified schematic of the proposed solution (IPP tech. variant). 5.3. PLASMA PHYSICS STUDIES 5.3.1.Density Fluctuation/mode analysis The fast hopping reflectometers were fully operational during the complete 2007 campaign. However, due to the break of EZ4 generator the campaign was postponed to May 2007 and the plasma scenarios were limited. The full tungsten machine program without boronization that was in place during the all campaign was not adequate for fast particle experiments and the relevant scenario was difficult to achieve. Nevertheless, discharges from earlier campaigns were analyzed. Further progress has been made in the study of fast particle and MHD modes. The radial eigenfunction of an n = 4 TAE (Toroidal Alfvén Eigenmode) was measured using the fast frequency hopping reflectometers. A phase and coherence analysis was used to estimate the radial displacement and density fluctuation level profiles from which the amplitude and sign of the radial eigenfunction are deduced. A comparison with CASTOR and LIGKA simulation codes shows excellent agreement. MHD modes (Washboard type) at the L to H-mode transition have been investigated. Parameter dependence and radial structure studies are currently in progress. 5.3.1.1. Alfvén eigenmodes Figure 5.4a shows the phase spectrum and the radial profile of δφ(f) for the n=4 TAE mode (solid line) for the shot #21007. The horizontal error bars indicate the uncertainty in the measurement of density profile obtained from Thomson scattering and Lithium Beam over the 165 ms time interval considered. The maximum peak in δφ(f) is around ρ pol ≈ 0.6 ± 0.05 with a less pronounced secondary peak at the edge. Figure 5.4b presents simulated radial eigenfunction obtained with CASTOR code. It was concluded that both the phase and coherence techniques are important and complementary. Figure 5.4a gives information on density fluctuation level Figure 5.4b provides the relative strength between different peaks plus the sign of the radial eigenfunction. Figure 5.4a - Reflectometer phase perturbation profile for the n=4 TAE mode, background profile and phase spectra (inset) for shot # 21007. Figure 5.4b - Simulated radial eigenfunction of radial plasma displacement for n=4 TAE mode from CASTOR code. Figure 5.5 depicts spectrograms from both the magnetics and reflectometry signals showing modes with upward frequency sweeping observed in the early phase of some discharges with ICRH power ramp-up and 34 identified as possible Alfvén cascades (ACs). The differences in mode frequency are due to some aliasing effects on reflectometry signals caused by the hardware analog filters. The radial extent of the TAEs derived from reflectometry is in good agreement with the results from the CASTOR code. Combining, the two hopping Q and V reflectometers, the chirping modes are core localized with ρ pol ≈ 0.2-0.4 (± 0.05). Further investigation aims at obtaining the radial eigen function of the ACs and compare it with LIGKA and CASTOR predictions. Figure 5.5 - Shot #20398: (a) FLQ-I spectrogram, (b) magnetic spectrogram and (c) time traces of ICRH and n e . 5.3.1.2. Edge MHD modes Figure 5.6 shows time traces of: (a) edge temperature, with time spectrograms of (b) FLV-I fixed frequency reflectometer and (c) Mirnov coil for ASDEX Upgrade shot #20393. Observed modes in H mode regimes can be either Wash board modes or Quasi-coherent modes. Both possibilities are being investigated. 5.3.2. ELM control studies The detailed characterization of the ELM dynamics has been pursuit using new data analysis technique applied to the broadband signals aiming at investigation the ELM triggering mechanism produced by the pellets (Figure 5.7). The evaluation of the ELM onset time with simultaneous plasma probing at both HFS/LFS has been done is in good agreement with MHD findings. Figure 5.6 - Time trace of (a) edge temperature, with time spectrograms of (b) FLV-I fixed frequency reflectometer and (c) Mirnov coil for ASDEX Upgrade shot #20393. Figure 5.7 - Density Layer method example for spontaneous and triggered ELM. Up to sixteen density layer radial displacements are plotted (density increases from red to violet). ELM onset time and pellet ablation time are indicated by dashed vertical lines. 35 5.3.3. Electromagnetic gyrofluid turbulence in the boundary region of tokamak plasmas The effect of the poloidal position of an axisymmetric Debye sheath (limiter cut) was studied computationally in the edge/SOL region 6 using the gyrofluid turbulence model GEM 7 . Furthermore, a geometrical model including an X- point-like singularity was developed specifically for the purpose of checking its effect (e.g., via its enhanced local magnetic shear) on egde turbulence. Initial results were obtained 8 . Complementary activities included the participation in the “EFDA Task Force on Integrated Tokamak Modelling” within the turbulence project (IMP4), and in the European DEISA project in collaboration with the Max-Planck-Gesellschaft Computer Centre (RZG). 5.3.3.1. Gyrofluid turbulence studies of the effect of the poloidal position of an axisymmetric Debye sheath This study was originally motivated by the results of the old ASDEX on single (one X-point) vs. double (two X-points) null configurations 9 . In line with those, the disconnection between the low field (LHS) and high field sides (HFS) of the SOL region, yield by using two limiter cuts in our computations (top and bottom of the torus – DN), led to a much more quiescent HFS (where the curvature is stabilising for interchange modes) than what was observed for the single limiter cut case (SN). In the latter, in contrast to the former, the fast Alfvenic dynamics was able to connect both sides of the SOL and govern the propagation of the “blobs” along the field lines. Such pronounced differences between the HFS and LFS are in principle also accessible experimentally on the ASDEX Upgrade tokamak, which can one or two X-points, and further allows for density fluctuations probing on both HFS and LFS simultaneously, via microwave reflectometry 10 . Qualitative experimental comparisons are foreseen for 2008. Independently of the limiter configuration, it was further observed that the turbulence measured in the SOL region was not being generated there, but rather in the edge region, which serves as a source. This is illustrated by Figure 5.8. However, due to the abrupt change in the parallel boundary condition upon entering the SOL, the turbulence changes character from the drift wave/ITG type in the edge to interchange in the SOL 11 , with the transition occurring over about 10-20 ρ s (sound gyroradius), which corresponds to roughly 1cm for the plasma parameters used. Figure 5.8 - Edge/SOL causality. Contours of as a function of radial coordinate (units of ρ s ) and time (in units of the sound speed c s over the background profile scale length L ⊥ ), averaged over the magnetic flux surface. The vertical dashed line at (x=0) represents the last closed flux surface. The orientation of the contours towards the upper right indicates turbulence propagation from the edge into the SOL, but not the opposite. The rightmost plot corresponds to an expanded time slice of the plot to its left, showing the time scale of a single event (about $40 L ⊥ c s , too short to be accountable to any linear instability local to the SOL 5.3.3.2. Self consistent MHD equilibrium in turbulence simulations This work was motivated by the necessity to treat self consistently the temporal evolution of the MHD equilibrium and turbulence together, on more realistic geometries that can impact the turbulence behaviour. The edge region plasma parameters are such that the equilibrium and turbulence interact strongly, and evolve together. The magnetic vector potential is a dynamical quantity evolved by an electromagnetic model (like GEM), which takes part in the MHD equilibrium (defined by the balances describing the Pfirsch-Schlueter currents, via the Ampere's law) as its axisymmetric component yields changes to the q-profile (field pitch), as well as the Shafranov shift. To study of the effect of the tokamak geometry, an increase in the sophistication involved in advancing the self-consistent equilibrium together the changing background profiles (pressure, electrostatic potential, etc.) was achieved. Starting from the earlier, simpler models 12 , involving two control parameters (S- alpha geometry 13 ), another more general model was introduced, involving circular magnetic flux surfaces, together with an analytical description for the X-point. 6 T.T. Ribeiro and B. Scott, Plasma Phys. Control Fusion 50: (accepted) 2008. 7 B. Scott, Phys. Plamsas, 12: 102307, 2005. 8 T.T. Ribeiro, 34 th EPS Conference on Plasma Physics, ECA Vol.31F, P-4.055, 2007. 9 M. Endler, Nucl. Fusion 35: 1307, 1995. 10 A. Silva, Rev. Sci. Instrum 67: 4138, 1996. 11 T.T. Ribeiro, Plasma Phys. Control. Fusion 47: 1657, 2005. 12 B. Scott, Contrib. Plasma Phys. 46: 714, 2006. 13 J.W. Connor, Phys. Rev. Let. 40: 396, 1978. 36 Such model was applied to gyrofluid turbulence computations including self consistent MHD equilibrium on local geometries by means of coupling the turbulence code GEM and the geometrical code METRICS 14 . Initial results were obtained (Figure 5.9), and the continuation of the work is planned. Figure 5.9 - (top) The local magnetic shear function along the magnetic field (s-coordinate) for both the S-alpha (constant line) and the circular model with an analytical description for the X- point that shows a the sharp spike. (bottom) The (spatial) three dimensional morphology o the electron temperature for the latter geometry model. There one sees the effect of the enhanced local shear caused by the X-point on twisting the turbulent structures as they extend along the field lines. This important effect is not included in the simpler S-alpha model. 5.3.3.3. EFDA Task Force on Integrated Tokamak Modelling activities Under the project IMP4 (Microinstability and turbulence), an effort was done to agree upoon standards for the input/output files in the HDF5 format, with the purpose of sharing data across different turbulence codes, a necessary step within the ongoing benchmarking activities. The implementation of the preliminary standard agreed upon in the local version of the GEM code has been done. 14 T.T. Ribeiro, 30 th EPS Conference on Controlled Fusion and Plasma Physics, ECA Vol. 27A, P-2.152, 2003. 44 full power) be installed from day-1 on ITER was advocated as the first part of a two-step modular approach to the LHCD system needed for the second phase of ITER (20 MW) – where it would then be reused. It aims at reducing the risks on a full system being introduced only at the 2020- 2025 horizon of the second phase and guaranteeing that competences would not be lost in this important and fully fusion specific field. 8.4.2. Stability studies for Tore Supra’s PAM Investigations have been started or resumed for Tore Supra’s PAM on the stability of its power splitting (at the output ports) as well as of its total reflection coefficient (at the input port) against changes in plasma loading conditions – translated to reflection coefficients on its output ports, ρ i . Figure 8.3 shows a simulation of the power splitting stability for the single module in Figure 8.2 at one of its 6 output ports (left) and on all 6 output ports (right), whereas Figure 8.4 portrays for the same module a simulation of the stability of the total reflection coefficient at its input port. Figure 8.2 - Electric field of the TE wave determined inside the waveguides of Tore Supra’s LH PAM launcher( prototype) module showing how the TE mode transmogrifies along this structure (the TE 10 -TE 30 mode converter is the undulating section on the right). Figure 8.3 - Power splitting stability of Tore Supra’s PAM+MC LH launcher module (in Fig. 1) as a function of the reflection coefficients at the output ports, ρ i : total electric field in amplitude and phase for port 1 (left) and in all 6 port (right). 45 Figure 8.4 - Stability of the (total) reflection coefficient at the input port of one of Tore Supra’s LH PAM+MC launcher modules as a function of the reflection coefficients at its 6 output port , ρ i (in amplitude and phase). 47 9. OTHER THEORY AND MODELLING STUDIES 1 F. Serra (Head), J.P. Bizarro (Deputy Head), R. Coelho, F. Nave, J. Ferreira and P. Rodrigues. 9.1. INTRODUCTION This project included in 2007 two research lines: • MHD stability studies; • Tokamak equilibria with toroidal current reversal. 9.2. MHD STABILITY STUDIES A non-linear MHD code, written in C-language, was developed to study the physics and strategies for the controlled feedback stabilization of neoclassical tearing modes in tokamak plasmas, a detrimental instability that degrades significantly the plasma confinement 2,3 . The numerical code, developed for a cylindrical geometry that replicates a large aspect ratio Tokamak, incorporates, besides pressure driven bootstrap current effects, the effects of plasma rotation and anomalous perpendicular viscosity. Code benchmarking was carried out for a wide variety of qprofiles in order to confirm typical linear growth rate scalings with magnetic Reynolds ( AR /S τ τ = ) and Prandtl ( VR /ττ=Γ ) numbers at zero plasma beta (Figure. 9.1). Extension to the non-linear regime and finite beta is currently being addressed. Figure 9.1 – Scaling of the linear growth rate of a (2,1) resistive tearing instability in cylindrical geometry with magnetic Prandtl number for S=10 5 . A large plasma viscosity is shown to stabilize the mode. 9.3. MODELLING OF TOKAMAK EQUILIBRIA WITH TOROIDAL CURRENT REVERSAL It has been found that solutions of the Grad-Shafranov equation displaying toroidal current reversal are not limited to small negative-current fractions nor to hollow pressure profiles. The equilibrium reconstruction tools developed previously 4,5 have been tested in a case where the ratio between negative and positive current-density peaks is about 0.4 and the plasma pressure has its maximum value on axis (Figure 9.2). In the first place, this shows that equilibrium reconstruction can robustly tackle large negative-current fractions, which may become an asset in future studies of AC-operated tokamaks. Secondly, it shows also that early predictions of hollow pressure profiles in the presence of toroidal current reversal 6,7 hold only if the flux-surface topology is nested, stressing the relevance of the axisymmetric island system when dealing with toroidal current reversal configurations. This relevance is further enhanced if the toroidal current density and the poloidal flux distributions are displayed simultaneously, as in Figure 9.3. There, two strong and positive current channels are clearly seen flowing through the high and low-field side islands, which may help to stabilize the negative one against small displacements. Figure 9.2 - Toroidal current density (left panel, solid lines) and plasma pressure (left panel, dotted lines) along the midplane, with the zeroth-order input profiles drawn in red and the computed distributions in black, together with the flux surfaces in the poloidal section (right panel, solid lines). 1 Activities carried out in the frame of the Contract of Association EURATOM/IST and the Contract of Associated Laboratory, by CFN staff of the Theory and Modelling Group. 2 Coelho, R. “Nonlinear growth of marginally unstable tearing modes”, Phys. Plasmas 14, 052302 (2007). 3 Coelho, R. and E. Lazzaro, “Effect of sheared equilibrium plasma rotation on the classical tearing mode in a cylindrical geometry”, Phys. Plasmas 14, 012101 (2007). 4 Rodrigues, P and JPS Bizarro, Phys. Rev. Lett. 95, 015001 (2005). 5 Rodrigues, P and JPS Bizarro, Phys. Rev. Lett. 99, 125001 (2007). 6 Chu, MS and PB Parks, Phys. Plasmas 9, 5036 (2002). 7 Hammett, GW, SC Jardin, and BC Stratton, Phys. Plasmas 10, 4048 (2003). 48 Figure 9.3 - Toroidal current density distribution Jf(R,Z) throughout the poloidal section (shaded surface). The lines of constant poloidal flux are first vertically deformed and then colored according to the value of Jf(R,Z), appearing as paths sloping up and downhill on the toroidal current density landscape. 49 10. OTHER ACTIVITIES ON CONTROL AND DATA ACQUISITION 1 J. Sousa (Head), C. Correia, A. Batista, M. Correia, N. Cruz, A. Duarte, J. Fortunato, R. Pereira, T. Pereira, D. Valcárcel. In parallel with the project-driven tasks, other research activities occur aiming to support present and future developments on the areas of control, data acquisition and signal processing. The following activities have been carried out in 2007:  Development and test of a high performance control and data acquisition platform based on the ATCA and PCIe standards.  Development of high-speed parallelized spectroscopy algorithms based on the trapezoidal filter method (Figure 10.1 shows the simulation results where 95% of total pulses were resolved in a scenario with 75% of pile-up events, at max. pulse rate, 20 ns pulses, using the HPD+DTS algorithms).  Development of a real-time Application Interface framework and debug/testing programs for the PCI Express bus under Linux real-time extensions (RTAI), focusing speed/throughput optimization.  Production of a fast timing and event management board for the PCI bus (EPN-PCI).  Development of an ATCA digitizer board with 12-bit resolution, 1 GSPS, 4 channels. Figure 10.1 - Spectra obtained by the simulation of 1000000 pulses with two energy amplitudes with periodic noise to cause spectral degradation (increases peak width), base line shift and 75% of pile-up events. PPD (peak pulse discriminator ) - the amplitudes were directly measured from the sampled data; DTS - the energy of pulses with and without pile-up; HPD - all the energy of pile-up pulses that couldn’t be resolved by DTS; HPD+DTS - the sum of the p1(n) with p2(n) outputs. 1 Activities carried out in the frame of the Contract of Association EURATOM/IST and the Contract of Associated Laboratory, by CFN staff of the Control and Data Acquisition Group. 51 11. KEEP-IN-TOUCH ACTIVITIES IN INERTIAL FUSION ENERGY 1 J. T. Mendonça, (Head), J. Davies, J. M. Dias, M. Fajardo, G. Figueira, R. Fonseca, A. Guerreiro, C. Leitão, N. Lopes, A.M. Martins, D. Resendes, J.A. Rodrigues, L.O. Silva. 11.1. INTRODUCTION The main results obtained in 2007 on keep in touch activities on inertial fusion energy during 2007 have been obtained along three different lines in ICF research: • Fast ignition and ICF theory; • High intensity photonics; • Plasma accelerators and intense radiation sources. 11.2. FAST IGNITION Keep in touch activities in IFE, with an emphasis on fast ignition of fusion targets, have covered (i) experiments conducted at the VULCAN Petawatt facility to understand the effects of laser intensity on the main features of the fast electron beam (e.g. divergence, energy), (ii) experiments on warm dense matter conducted at PALS (iii) theory on magnetic field generation due to plasma expansion in laser-solid interactions, (iv) transition from the collisionless to the collisional regimes in the electromagnetic filamentation instability in fast ignition, and (v) theory and numerical work on the temporal growth rates of Stimulated Raman Scattering in the presence of light with statistics typical of ICF scenarios. 11.3. HIGH INTENSITY PHOTONICS Several ytterbium-doped laser media were tested and characterized in a diode-pumped, mJ-level regenerative amplifier as a possible independent medium-energy beam for experiments and to assess their features for a diode based beam line. Additionally, a high performance diode stack for high energy and high intensity pumping, able to deliver 4 kW, 3 ms pulses at 10 Hz, was acquired. This will allow an increase from the mJ pulse energy from the current regenerative amplifier to the 100 mJ level. Together with the developed full modelling of the temperature, pump and amplification (Figure 11.1), we are now ready to test new and promising ytterbium-doped laser materials, as well as to provide a medium-energy pump pulse for optical parametric chirped-pulse amplification (OPCPA) setups. With regard to this technique, we are able to demonstrate experimentally the advantages of the dispersed-signal geometry for generating ultra-broadband (>500 nm), high-energy pulses, capable of leading to ultrahigh intensities in the few-cycle pulse regime. Figure 11.1 - Calculated spectral shift and narrowing of a laser pulse initially centered at 1053 nm as a function of the number of passes in a diode-pumped Yb:glass regenerative amplifier. The numerical code takes into account the full pump and seed pulse parameters, and the optical, material and thermal properties of the gain medium. At the level of diagnostics development, a new wavefront sensing diagnostic and a novel patented deformable mirror were installed, for optimizing the focal spot of the high power multi-terawatt laser system at IST, leading to intensities on target in the range of 10 19 W/cm2 A permanent suite of diagnostics was installed before and after final pulse compression. These include a calibrated photodiode for energy measurement, a near-field CCD camera for monitoring the beam profile before compression, a far-field CCD after the compressor, a radial shearing interferometer and a second-order single-shot autocorrelator. 11.4. PLASMA ACCELERATORS AND INTENSE RADIATION SOURCES The activities on this topic have covered the following aspects: (i) experiments on plasma waveguiding, including full characterization of the devices at low power, and demonstration of guiding at high intensity, and (ii) implementation, experimental demonstration, and implementation of a high harmonics source from laser-gas interaction at IST, with the existing laser parameters, with single shot harmonic generation up to the 47 th harmonic. 1 Activities carried out in the frame of the Contract of Association EURATOM/IST and the Contract of Associated Laboratory, by “Grupo de Lasers e Plasmas” (Golp) of “Centro de Física dos Plasmas”. 53 12. PARTICIPATION IN THE FUSION TECHNOLOGY PROGRAMME 1 C. Varandas (Head), E. Alves, L.C. Alves, N.P. Barradas, M.R. da Silva. 12.1. INTRODUCTION This project included in 2007 activities in the frame of Underlying Technology and of the Tasks referred to in Table 12.1. The work carried out in ITER-specific tasks is described in chapter IV. Task Area Beginning TW5-TPDS-DIARFA ITER diagnostics 07.09.2005 TW5-TTMS-006 Structural Materials 09.03.2005 TW6-TPP-ERDEP Plasma-Wall Interaction 12.10.2006 TW6-TDS-QA2 Quality Assurance 08.12.2006 TW6-TPDS-DIADES ITER diagnostics 08.12.2006 TW6-TVR-WHMAN2 Remote Handling 01.09.2007 TW6-TTFF-VP75-2 Fuel Cycle 01.09.2007 Table 12.1 – IST tasks in the Fusion Technology Programme 12.2. MATERIAL CHARACTERIZATION USING NUCLEAR TECHNIQUES: TITANIUM BERYLLIDE OXIDATION STUDIES Be alloys are under intense research due to its potential to replace pure Be as functional material on Fusion reactors. However allowing Be with transition metals is difficult and there is a lack of knowledge about its behavior. In this work we continued the study of the structural properties of these intermetallic compounds with emphasis on the oxidation behavior. The samples were characterized with Electron microscopy (SEM), X-ray diffraction and Ion beam analyses (IBA). The thermal stability and oxidation behaviour at high temperatures under air annealing was studied with emphasis on the oxidation kinetics aiming at understanding the physical mechanisms underlying the oxidation process. The surface of each of the samples was polished and the oxidation was accomplished by annealing at 800º C in air atmosphere. The RBS results. (Figure 12.1) reveal for the 5at%Ti sample, not only that the oxidation occurs preferentially at the Ti depleted (Be rich) zones but also that the oxide layer formed in the time step annealing is smaller than the one formed in single step annealing, even if we reach the same annealing time. The elemental distribution map of Ti, (Figure 12.2) shows that topography changes are noticeable for the single 8 h annealing procedure, indicating that the Be diffusion continues even if the oxide layer doesn’t seem to change that much, as shown in the spectra of Figure 12.2. Our results clearly indicate that oxidation of Beryllides occurs preferentially along the Be richch zones and seems to be a continuous process. 200 400 600 800 1000 0 20 40 60 80 100 120 140 O Ti Be Be 5Ti Ti+ virgin 800ºC 2h+2h+4h 800ºC 8h Counts Channel 200 400 600 800 1000 0 20 40 60 80 100 120 140 160 180 200 220 240 O Be Ti Be 5Ti Tivirgin 800ºC 2h+2h+4h 800ºC 8h Counts Channel Figure 12.1 – RBS point spectra from the Be 5at%T i sample before and after annealing procedures, obtained in the T i rich region (top) and in the T i depleted (bottom) zones. 12.3. TASK TW6-TPP-ERDEP - STUDIES OF MATERIAL EROSION AND REDEPOSITION IN ITER-RELEVANT DIVERTOR TARGET TEMPERATURES, PLASMA IMPACT ENERGIES AND DIVERTOR CHAMBER GEOMETRIES. Delivery D3-Report on the effect of ITER-relevant material mixing on fuel retention and material characteristics Previous studies have shown W to have favorable H/D/T retention characteristics. However, the ion flux densities in these experiments were well below the levels expected in the ITER divertor. Furthermore the behaviour of H/D/T retention as a function of fluence is critical in determining the retention saturation level for a W PFC in ITER. 1 Activities carried out in the frame of the Contract of Association EURATOM/IST, by staff of “Instituto Tecnológico e Nuclear”. 54 2+2+4h 8h virgin 2+2+4h2+2+4h 8h virgin Figure 12.2 – T i elemental distribution maps from the Be 5at%T i sample obtained before and after annealing procedures, showing complete modification of surface structure after 8h annealing in air. The maps have dimensions of 530 × 530 µm 2 except for the bottom-right that is a zoom of the bottom-left map and presents dimensions of 264 × 264 µm 2 . The major goal of the study was the full characterisation of the surface composition and morphology and fuel retention of W targets exposed to plasma fluxes similar to the ones expected in the ITER divertor (>10 23 m -2 s -1 ). Tungsten samples were exposed to plasma fluxes in PSI-2 and studied with ion beam techniques and atomic force and electron microscopy. Fuel retention in the samples and its depth distribution was quantified with Elastic Recoil Detection Analysis (ERDA) and Nuclear Reaction Analyses (NRA). W targets with 1mm thick, 20 mm diameter discs in thermal contact with a water-cooled copper heat sink and electrically grounded were exposed to deuterium plasma in the Pilot-PSI. This linear plasma generator produces plasma conditions that are expected to be typical at a detached ITER divertor strike point (n e ~ 10 20 D + m -3 , T e < 5 eV, Γ D+ ~ 10 24 D + m -2 s -1 ). Deuterium retention in W was measured as a function of incident plasma fluence at a plasma flux density in the ITER divertor range (Γ D+ ~ 10 24 D + m -2 s -1 ). The W targets exposed in Pilot-PSI were analysed ex-situ with 3 He(d,p)α nuclear reaction analysis (NRA) and thermal desorption spectroscopy (TDS). While NRA provides D depth profiles and concentrations over the first ~3 µm TDS gives information on global/bulk retention and trap mechanisms and energies. Initial NRA data, Figure 12.3 shows a D depth profile that is peaked at the surface and significant D retention (0.01 at. %) at a depth of ~3 µm after only 40 s (10 discharges) of total plasma exposure time. This demonstrates the trapping of D that has diffused away from the ion implantation zone towards the bulk. The effects of surface polishing/roughness and preannealing targets before plasma exposure are investigated through the comparison of D retention as determined by NRA and TDS analysis. The results show that a W target with a surface roughness of <1 µm has nearly 6 times more D retention in the first 3 µm of the surface than an “as received” W target. 100 150 200 250 300 0 100 1.0 MeV Channel P5 Yield (counts) VII 0 100 2.0 MeV Yield (counts) 0 100 200 2.3 MeV Yield (counts) 0 500 1000 1500 2000 2500 3000 3500 4000 0.00 0.02 0.04 0.06 0.08 0.10 0.12 0.14 [d] (at.%) Depth (nm) VII Figure 12.3 - Alfa spectra from the 3 He(d,p)α nuclear reaction for the energies indicated in the panels (top). The solid line is the simulation obtained with the NDF code and the peak observed at higher channels is due to the pile-up effect at the end of the depletion layer of the Si detector. The D depth profile extracted from the experimental spectra is shown on the bottom. 55 13. OTHER FUSION-RELATED ACTIVITIES 1 C. Varandas (Head), H. Fernandes, M.E. Manso, A. Silva, J. Sousa, I. Carvalho, J. Fortunato, S. Magalhães, L. Meneses, A, Neto, T. Pereira, J. Santos, A. Soares, D. Valcárcel. 13.1. INTRODUCTION This project included activities related with the collaboration of IST/CFN with IPP.CZ, IPP-Greisfwald, Brazilian Institutions and ENEA-Frascati as well as activities on socio-economics, education and training, organization of scientific meetings and management of the EURATOM Fusion Programme. 13.2. COLLABORATION WITH IPP.CZ 13.2.1. Introduction This research line included in 2007 work on microwave reflectometry and control and data acquisition. 13.2.2. Microwave reflectometry The following activities were carried out:  Elaboration in June 2007 of a first conceptual design of a FM-CW reflectometer system for the Compass tokamak, using in-vessel antennas and separate waveguides for each of the four frequency bands;  Elaboration in October/November 2007 of a new design using ex-vessel antennas and two complex transmission lines to launch and receive all the frequency bands, including combiners and decombiners, to be compatible with the reduced access available at Compass-D, which was only known after the tokamak drawings were received at IPP.CR;  Design of the combiners/decombiners and lenses (Figure 13.1);  Beginning of the assessment of the system proposal (Figure 13.2) in terms of cost and time schedule. Figure 13.1 - Arrangement of the quasi-optical band-combiner 13.2.3. Control and data acquisition The following tasks were performed:  Development of the control and data acquisition system for COMPASS including hardware prototypes and software programs;  Assessment and overall design of the CODAC system and some of related sub-systems (Figure 13.3);  Preliminary instrumentation and operation software tests on ISTTOK an JET-EFDA. 13.3. COLLABORATION WITH IPP-GREISFWALD 13.3.1. Introduction This collaboration started in 2007, with work on tomography diagnostics and control and data acquisition. 13.3.2. Tomography diagnostics  Beginning of the development of a neural-network for tomography systems. The neural-networks algorithm 2 required training with artificial data (phantoms), for W7-X that has been processed to generate the neural network. These phantoms were rings placed at different positions and with different radii; ‘zero’ radius was included, yielding a gaussian emissivity profile. Tests with noisy artificial data suggest it to be robust and accurate;  Implementation for W7-X, with good results for artificial data, minimum Fisher regularisation algorithm. Due to generalization of the code, it can easily be adapted for other machines such as W7-AS. 13.3.3. Control and data acquisition It was agreed to install an ATCA system to show the feasibility of real time processing for some diagnostics of W7-X, namely the magnetics and tomography 13.4. COLLABORATION WITH BRAZILIAN INSTITUTIONS 13.4.1. Introduction IST has maintained the collaborations with the TCA/Br 3 and ETE 4 programmes in the areas of microwave reflectometry, control and data acquisition and Thomson scattering. 13.4.2. Microwave reflectometry The following tasks were performed:  Selection and placement of orders for the millimetrewave components of the broadband reflectometer of TCA/Br; 1 Activities carried out in the frame of the Contract of Association EURATOM/IST and the Contract of Associated Laboratory. 2 Supplied by S.Gori and U. Toussaint, from IPP-Garching 3 TCA/Br is a tokamak of the “Laboratório de Plasmas, do Instituto de Física, da Universidade de São Paulo. 4 ETE is a tokamak of the “Laboratório Associado de Plasmas, do Instituto Nacional de Pesquisas Espaciais, de São José dos Campos”. 56 Figure 13.2 - Block scheme of O-mode 18-26.5 GHz transmitter and receiver Figure 13.3 - Global diagram of the COMPASS CODAC system.  Building ant testing of the tuning ramp generators, HTO drivers and the controller board;  Design and starting of the fabrication of the IF detection amplifiers. 13.4.3. Control and data acquisition The following activities were made:  Remote support of the operation of the ETE data acquisition system;  Elaboration of a proposal for the development of a set of VME transient recorders for TCA/Br. 13.4.4. Thomson scattering The following tasks were carried out:  Testing at the University of São Paulo of the ISTTOK Nd:YAG laser;  Design and construction of part of the system to deliver the laser beam to the TCA/Br tokamak. 13.5. COLLABORATION WITH ENEA-FRASCATI This collaboration included work related with liquid metal limiter plasma interaction and control and data acquisition. The following activities were carried out in 2007:  Participation in FTU experiments for plasma liquid lithium limiter interaction studies. Analysis of the achieved results have shown a significant improvement of the plasma discharge, with lower plasma contamination by impurities, lower radiated power and higher plasma densities. 13.6. SOCIO-ECONOMIC STUDIES TIMES was installed at IST by experts of EFDA-TIMES. A group (1 pos-doc and 3 PhD students) was created at IST to develop energy models with emphasis on the analysis of the sustainability of the energy systems at different scales. 64 region of the target. For such highly non-linear phenomena there is no theory and particle in cell (PIC) modeling appears as the main tool for its study. 14.11 - Beam electron density temporal evolution: onset of the WI and filament coalescence. The interaction of a PW laser pulse with a pre-ionized target has been studied resorting to two-dimensional PIC simulations that have been performed with Osiris 2.0 20 . A parametric scan of the target density and thickness has been carried out in order to understand the importance of these parameters for the laser energy absorption and for the electron filamentation in the target. The angular distribution of the relativistic electrons generated through the interaction of the PW laser with the preformed plasma has been studied. Preliminary results from PIC simulations show that the divergence angle of the filaments ranges from 20º to 30º for target densities ranging from 30 n c to 10 n c , respectively (Figure 14.12). For target densities of 10 n c , laser filamentation has been observed along with electron filamentation in the target. At 30 times the critical density, laser filamentation does not occur, though electron filamentation has been observed. Figure 14.12 - Results from PIC simulations for the electron density (shaded) and laser electric field (contours) at the peak of the PW laser pulse using a 10 n c 50 µm thick target (top) and a 30 n c 50 µm thick target (bottom). 14.5. ASTRO AND SPACE PHYSICS 14.5.1. Solar energetic particle production in coronal mass ejection shocks 21 Acceleration mechanisms of solar energetic particles are usually associated with Coronal Mass Ejections (CME) in the solar corona environment. CME structures propagate at speeds up to 2000 km/s, interacting with the slower solar wind and creating a shock. As the CME structures have a frozen-in magnetic field, both parallel and perpendicular shocks are formed with the solar wind. Two simulation setups, mimicking the corona environment, were used to capture the physics of the accelerating particles. In the first scenario the solar wind flows quasi-parallel to the background magnetic field and a slab of plasma is shocked against the solar wind plasma. In the second more realistic scenario, the frozen-in magnetic field in the CME zone is also included. Simulations show the formation of Alfvèn-like waves upstream of the shock, in the solar wind, due to the quasi-parallel flow (Figure 14.13). These waves interact with the coronal mass ejection particles through wave-particle interaction, accelerating them mainly in the perpendicular directions through a surfatron like mechanism, but also in the shock direction. Figure 14.13 - Electric field intensity of a CME quasi-parallel shock showing wave formation in the solar wind. Quantities are expressed in normalized simulation units. 14.5.2. Energetic ion interaction with mini magnetospheres 22 Solar energetic ions, originating from Coronal Mass Ejections and Solar Flares, have energies up to several GeV and are a known hazard to both spacecraft electronics and to manned space flights, particularly in space missions that extend over a long period of time like interplanetary missions. Laboratory experiments and simulations were performed to assess the feasibility of using a dipole like magnetic field, in conjunction with a plasma source, to provide effective means of protecting a spacecraft against solar energetic ions. Preliminary experimental results show a plasma beam being deflected by a dipole like magnetic field generated by a permanent magnet, and a mini magnetosphere being generated (Figure 14.14). A simple theoretical model, 21 Work developed in collaboration with R. Bingham, Rutherford Appleton Laboratory, UK. 22 Work developed in collaboration with R. Bamford and R. Bingham, Rutherford Appleton Laboratory, UK. 65 balancing plasma dynamic pressure with the magnetic pressure from the dipole field, provides means of calculating the plasma standoff distance from the center of the dipole field. In the simulations performed with dHybrid 23 , results show the plasma deflection distance increasing with the density and magnetic field intensity, and decreasing with the plasma flow velocity, as expected from theory. Figure 14.14 - Plasma density cut of the simulation of the laboratory experiment showing the plasma being pushed out of the dipole field region. Plasma is flowing from the left, and the magnetic moment of the dipole magnetic field is oriented in the +z direction. 14.5.3. Ultra-relativistic flows and particle acceleration in astrophysics Ultra-relativistic flows are pervasive in astrophysics, leading to the formation of relativistic shocks, particle acceleration to extreme energies, and generation of intense radiation. Due to the strong nonlinear and kinetic effects, a self-consistent description of relativistic shocks and of particle acceleration in these nonlinear structures is still missing as one of the unsolved problems in astrophysics 24 . Leveraging on the new diagnostic tools for particle tracking available in Osiris 2.0, a detailed numerical study of these shocks was performed, identifying the critical regions of particle acceleration both in the precursor and shock-front regions (Figure 14.15). Figure 14.15 - Magnetic field energy for two electron-ion plasmas flowing through each other; current filaments and magnetic fields are generated by the Weibel instability. 14.6. HIGH PERFORMANCE COMPUTING 14.6.1. Particle tracking diagnostics in PIC codes The field of laser plasma acceleration has witnessed significant development over recent years, with experimental demonstrations of the production of quasi mono-energetic electron bunches, with charges of ~ 50 pC and energies of up to 1 GeV 9 . These accelerators require no external injectors, and recently it has also been shown experimentally that the self-injection mechanism can be controlled 25 . Given the highly nonlinear and kinetic processes involved during high-intensity laser beamplasma interactions, fully relativistic particle-in-cell (PIC) codes, such as Osiris 2.0 20 are the best tools for modeling of these physical problems. However, PIC codes per se are not enough and sophisticated visualization and data analysis routines 26 are required to extract physical meaning from the large volumes of data being produced. A complete and detailed understanding of self-injection mechanisms in the Laser Wakefield Accelerator (LWFA) is yet to be achieved and to that end a detailed knowledge of single particle evolution in the accelerator is critical (Figure 14.16). To this end a particle tracking diagnostic was developed for Osiris 2.0 20 , but that can be easily ported to work with other codes. Generally the simulation needs to be run twice; once to determine which are the particles worth tracking and a second time to save the actual tracking information. If only low temporal resolution is required these tracks can also be extracted from standard particle dumps. Figure 14.16 - Braided Trajectories in 3D phase space of injected particles in the LWFA. Given that we are searching for groups of several hundreds of particles in a set of tens of millions, the main obstacle to this diagnostic was performance. Searching for the particles being tracked at every time step would represent an immense computational cost, especially when parallel issues are considered. To overcome this issue a novel technique was devised that effectively eliminates the overhead of particle tracking. 14.6.2. Data visualization environment The present visualization and data analysis tools 26 , available for use with our suite of codes, have been successfully applied to datasets ranging up to a Terabyte in size. However, despite representing a major leap in 23 Gargaté L, Bingham R, Fonseca RA, Silva LO, Comput. Phys. Comm. 176, 419 (2007). 24 Piran T, in “Unsolved Problems in Astrophysics”, (eds. J. N. Bahcall and J. P Ostrker), Princeton: Princeton University Press, p. 343 (1997). 25 Faure J et al, Nature 444, 738 (2006). 26 Fonseca RA, Proceedings of ISSS-7 (2005). 66 scientific visualization for particle in cell (PIC) codes, these routines have some limitation in terms of interactivity and simultaneous representation of multiple datasets. The new Data Visualization Environment being developed, while maintaining the previous ease of use and quick presentation quality plots, is being developed from scratch to address these issues (Figure 14.17). The visualization space can hold an unlimited number of data sources, and an unlimited number of visualization objects that represent them. As before, all annotations, including labels and units, are automatically generated from the metadata available in the input files, and the plot dimensions are set to better display all information. This new visualization environment also allows for interactive data analysis, such as Fourier transforms of grid data or data mining of particles, and for time navigation. Movie generation as also been improved, with all options being available interactively. Figure 14.17 - New visualization toolkit, presenting multiple simultaneous datasets (density, laser field, and particles) and time navigation 14.6.3. IT infrastructure A wide range of information technology (IT) infrastructure is installed and maintained by the our team. The current infrastructure ranges from computer and office networks over web-servers up to high performance computing (HPC) clusters. Services embedded into this infrastructures include desktop computing, web-hosting for the IPFN, GoLP, and epp web-pages, hosting and maintenance of code repositories, availability and access of HPC resources, storage and accessibility of simulation data, online diagnosis and management of the HPC infrastructure, and online visualization of intermediate simulation results. 14.6.4. IST Cluster The IST Cluster is an IBM Cluster 1350 computing system consisting of seventy dual-CPU, dual-core Power5 JS21 blades with 2 GByte of memory per core, running the AIX 5.3 operating system, interconnected by dual gigabit Ethernet (Figures 14.18 and 14.19). Figure 14.18 - Front view of the IST Cluster (picture: Michael Marti). Figure 14.19 - Interconnect: one of the core components of a distributed memory machine (picture: Michael Marti). Ever since the very beginning of the IST Cluster, members of our team showed a strong interest in this project. It is for this reason that our team provided and still provides a major part of the manpower and effort necessary for the installation, deployment and maintenance of the IST Cluster. Amongst the tasks done by our team during the installation and deployment phase are: basic hardware and software installation, setup and maintenance of a set of administrative scripts allowing for a decentralized user administration, preparation, test and deployment of the HPC core services (compilers, parallel libraries, performance libraries), configuration of the resource manager, definition and implementation of the policy structure for the job scheduler, and others. Ongoing tasks include: periodic hardware maintenance, software updates, fine tuning of user environments and policy settings, and naturally supporting the several users in the usage of the available infrastructure. 14.6.5. Exposing stream processors as Grid services with a GPGPU example 27 Recent graphics processing units (GPUs) with single instruction, multiple data (SIMD) and multiple instruction, multiple data (MIMD) capabilities have shown to provide good performance not only on streaming applications as well as on applications that have sufficient parallelism and computational intensity to hide memory latency. Another SIMD/MIMD processor that has recently been introduced is the Cell Broadband Engine Architecture (Cell processor), from Sony, Toshiba and IBM (STI), which has shown tremendous potencial for the scientific community, in terms of performance and power efficiency 28 . Integrating such fine-grained stream resources in a Grid 27 Work developed in collaboration with J.M. Pereira, IST/INESC-ID, Portugal. 67 system as a general computational resource or service is an important way to significantly increase a Grid’s performance and computing power at very little cost. As an integration example, we used the already tested simplified Boris particle pusher, which was previously adapted to general purpose computation on GPU (GPGPU) code 29 . This time, this GPGPU algorithm was implemented on commodity hardware that is normally used as part of a Grid node for plasma physics simulation. On one processor, we achieved 4–5 frames per second (fps), which is comparable to the performance on the CPU. Simulations run on a system with two Worker Nodes showed a very good performance gain, since this simplified Boris pusher requires a minimal node communication Figure 14.20). With 4 particles per cell (ppc) we achieved 8–9 fps with two GPUs and with 8 ppc the system kept a steady 4 fps. These results showed that it is very useful to expose the SIMD capabilities of GPUs on a Grid. Figure 14.20 - Real-time visualization of the results of the GPGPU implementation of the simplified Boris pusher. From a down-up approach, the first place to expose these capabilities is at the schema used to announce the Computing Element (CE) to the rest of the Grid. As specified in the GLUE schema specification 30 , a processor type is described in the SubCluster entity, with specific attributes divided in two sub-entities: Software and Host. The host entity has attributes such as ProcessorModel, ProcessorInstructionSet and ArchitecturePlatformType, that can be used to uniquely define a SubCluster of GPU’s (or other commodity stream processors). The attributes of the Software entity can further clarify the capabilities supported by the processor, giving extra granularity in selecting a correct software version or environment. A SubCluster of this kind could have a dedicated queue, which means it would be visible to the outside as a set of job slots belonging to a certain CE. Another possibility is to assign this kind of SubCluster to a whole CE, which means that all the jobs slots of this CE would be for stream processing, thus defining a CE specific for streaming computation. Acting at the schema level allows all the relevant parts possibility is to assign this kind of SubCluster to a whole which means that all the jobs of Grid middleware to have access to this information. Both the push model (where jobs are pushed to a CE and the pull model (where the CE asks the Workload Management Service for jobs) would work, and high-level application tools (such as P-GRADE or GENIUS) can easily be made aware of this kind of processors. Since the GLUE schema is widely used in Grids (e.g., in EGEE’s gLite or in Globus), this approach is valid for different Grid middleware. 14.6.6. Remote visualization on the IST Cluster A software system for remote visualization on the IST Cluster was implemented based on VisIt (Figure 14.21), an interactive tool for parallel visualization and analysis of scientific data from Lawrence Livermore National Laboratory, USA. Figure 14.21 - Visit running on IST Cluster. 14.6.7. Hybrid code development for massively parallel applications 31 Hybrid codes, using kinetic ions and a neutralizing electron fluid, are useful in space plasma scenarios, where the ion time scale needs to be properly resolved and the high frequency modes on the electron time/length scales are not thought to play a significant role. In dHybrid 23 we implement a space and time centered explicit hybrid algorithm, using massless electrons, neglecting the electron pressure term and neglecting the displacement current in Ampère’s law. The algorithm is fully parallelized using spatial domain decomposition and employing the MPI libraries for inter process communication. Space plasma simulation scenarios often lead to situations where there is a large particle imbalance between different volumes of the simulation space; the particle imbalance leads to severe loss of performance, some nodes finishing their calculations much sooner than other nodes. To boost performance, dynamic load balancing was added to dHybrid: parallel spatial partitions computational charge. Performance boosts up to 40% are achieved, depending on the problem in hand. 28 Williams S, Shalf J, Oliker L, Kamil S, Husbands P, and Yelick K, “The potential of the cell processor for scientific computing”, in CF ’06: Proceedings of the 3 rd Conference on Computing Frontiers, pages 9–20, New York, NY, USA, 2006, ACM Press. 29 Abreu P, Pereira JM and Silva LO, “A Distributed Memory GPU Implementation of the Boris Particle Pusher Algorithm”, in “Eurographics Symposium on Parallel Graphics and Visualization” 2006, Braga, Portugal. 30 Andreozzi S, Burke S, Donno F, Field L and Fisher S, in “Glue Schema Specification”, 2007, http://glueschema.forge.cnaf.infn.it/Spec/V13. 31 Work developed in collaboration with R. Bingham, Rutherford Appleton Laboratory, UK. 68 14.7. COMPUTATIONAL PHYSICS 14.7.1. Monte Carlo simulations of relativistic collisions in plasmas 32 The statistical analysis of many-particle systems in the relativistic domain is a fundamental research topic still lacking conclusive results. Even in the simple case of a dilute gas, describable by Boltzmann’s equation, conflicting results on fundamental issues, such as the validity of the standard Jüttner distribution function (the “relativistic Maxwellian”) repeatedly appear in the literature (cf. 33 ). The Monte Carlo simulation techniques developed at GoLP revealed the source of the conflicting results in the literature and provided a general recipe to simulate relativistic collisions in a way that is consistent with special relativity, thus always obtaining the Jüttner distribution function. Simulations with Osiris 2.0 confirmed the validity of the Jüttner distribution in ultrarelativistic scenarios. 14.7.2. Numerical studies with particle-in-cell codes in boosted frames 34 A recent work by J.-L. Vay 35 demonstrated the possibility of reducing numerical simulation times by orders of magnitude, by performing the simulation in a Lorentz boosted frame. This scheme completely changes computational resources required for long simulations in several topics of state-of-the-art research, such as laser/plasma interaction, astrophysics relativistic outflows and undulator/wiggler modeling. The necessary numerical algorithms for Lorentz transformation between relativistic frames and the specific diagnostics needed for data analysis were implemented in Osiris 2.0, for direct application in Laser Wakefield Plasma Accelerators (LWPA) and relativistic outflows simulations (Figure 14.22). The necessary time for processing was typically reduced by factors above one hundred. Figure 14.22 - Example of plasma “bubble” and particle injection in a boosted frame. 14.8. RADIATION GENERATION 14.8.1. Phase-matched even-harmonic generation in relativistic ionization fronts In underdense plasmas, phase-matched second-harmonic generation is possible in the presence of a modulated magnetic field 36 . However, the required conditions for the magnetic field are demanding due to the short wavelength of the B-field modulation and the high B-fields required. A novel scheme to generate even harmonics in uniform transparent plasmas has been studied. This scheme uses the magnetic mode 37 generated in the collision of electromagnetic radiation with a relativistic ionization front, driven by an intense laser pulse propagating in a gas target, to provide the magnetic field required for phasematching. A theoretical model has been developed, predicting the phase-matching conditions, describing the evolution of the amplitude of the second harmonic, and determining the features of the ionization front and of the colliding pulse required to generate a magnetic mode appropriate for relativistic even-harmonic generation. In order to check the validity of the model, detailed one-dimensional and two-dimensional particle-in-cell (PIC) simulations have been performed with Osiris 2.0. The analysis reveals a good agreement between the theoretical model and the simulation results. The magnetic mode has been observed to provide the required B-field for even-harmonic generation. The conversion efficiency of the process has also been studied, indicating the possibility of achieving controlled, short and intense, even-harmonic generation (Figure 14.23). 14.8.2. Radiation generation in the interaction of intense pulses with nanowires Clusters, nanowires and other nano-structures represent an interesting medium to produce radiation by the irradiation of dense nanoplasmas with intense laser pulses. When small clusters or nanowires are hit by ultra-short laser pulses, their electrons can be completely removed or oscillate in the ion core potential, depending on the intensity of the laser field. This oscillatory motion of the electrons can lead to the generation of harmonic radiation 38,39 . The radiation emitted when a nanowire is hit by an ultra-short ultra-intense laser pulse (with 800 nm wavelength, pulse duration of ~3 cycles at FWHM and peak intensity 5×10 19 W/cm 2 ) was studied using twodimensional particle in cell (PIC) simulations performed with Osiris 2.0 and a power spectrum diagnostic 40,41 . 32 Work developed in collaboration with G. Coppa, Politecnico di Torino, Italy. 33 D. Cubero et al, Phys. Rev. Lett. 99, 170601 (2007). 34 Work developed in collaboration with W. Lu and W.B. Mori, University of California – Los Angeles (UCLA), US. 35 Vay J-L, Phys. Rev. Lett. 98, 130405 (2007). 36 Rax JM et al, Phys. Plasmas 7, 1026 (2000). 37 Lampe M et al, Phys. Fluids 10, 42 (1978). 38 Antonsen TM Jr. et al, Phys. Plasmas 12, 056703 (2005). 39 Fomyts’kyi MV et al, Phys. Plasmas 11, 3349 (2004). 40 Kazeminejad F, PhD thesis, UCLA (1986). 41 Dawson JM, Rev. Mod. Phys. 55, 403 (1983). 69 14.23 - Wigner distribution of the laser driver (top) and Wigner distribution of the second-harmonic (bottom) after a propagation distance of 767 µm. It was found that in the case of thin nanowires (30 nm radius) the electrons are completely removed from the ion core by the laser pulse, generating a short-duration radiation burst as they leave. At these intensities, the ponderomotive displacement is so strong that it prevents the electron cloud from returning to the ion core and less than one oscillatory cycle is executed. The amplitude of the radiation generated is stronger in the direction of the velocity of the electron cloud as expected for relativistic electrons (Figure 14.24). A parameter scan was performed to understand the influence of the electron density and the nanowire radius on the spectrum of the radiation, in particular as the diameter approaches the scale of the laser wavelength. Experiments performed with ethanol droplets hit by intense laser pulses have shown that submicron-scale targets interact differently from nanometer-scale clusters 42,43 . In the scenarios studied here, nanowires of 30, 100 and 300 nm radius and densities of ~2 n cr and ~5 n cr were irradiated by an ultra-intense ultra-short laser pulse (same parameters as above). In the cases of small or intermediate radius, results were similar. The electrons were removed from the cluster either in a single or multiple bunches, each of these generating a burst of radiation as they left the ion core. As for the larger nanowires, while in the 2 n cr scenario the larger radius only resulted in more bunches being extracted, in the 5 n cr case the laser was not able to remove bunches of electrons. Instead, a high electron density region was formed in the area first hit by the laser. The electrons from this region were transported along the nanowire surface accelerating to high energies (up to few MeV), radiating along this motion. Sub-wavelength electron density perturbations were also observed inside the nanowire as well as surface rippling. Figure 14.24 - Magnetic field in x3 direction (upper figures) and electron density (bottom figures) of clusters irradiated by an 800 nm wavelength 3-cycle laser pulse with peak intensity of 5×10 19 W/cm 2 ; the targets are deuterium nanowires with a radius of 300 nm and electron densities of 1×10 22 cm -3 and 4.6×10 22 cm -3 . 42 Gumbrell ET et al, Phys Plasmas 8, 1329 (2001). 43 Symes DR et al, Phys. Rev. Lett. 93, 145004 (2004). 70 The power spectrum of the radiation emitted following the irradiation of an array of periodically aligned thin (30 nm radius) nanowires by an ultra-short ultra-intense laser pulse was also studied (Figure 14.25). It showed an increase in the signal of the emitted radiation at multiples of the spatial frequency of distribution of the nanowires. This should be due to constructive interference of the radiation emitted by the different nanowires. Figure 14.25 - On the upper, the magnetic field in x3 direction exhibits the radiation bursts generated as the laser hits successive nanowires. On the bottom, the power spectrum of the electromagnetic waves propagating perpendicularly to the laser pulse shows higher amplitude components at multiples of the spatial periodicity of the nanowires in the array. 71 15. HIGH DENSITY LASER PLASMA PHYSICS 1 L.O. Silva (Head), J.R. Davies (Deputy Head) , M. Fajardo, F. Fiúza and J. Valente. 15.1. INTRODUCTION The work on High Density Laser Plasma Physics was focused on:  Design work for HiPER;  Analysis of Results from Laser-Solid Experiments on the Vulcan PW;  Filamentation in laser ablation of solids;  Integrated numerical design of laser-plasma experiments. 15.2. DESIGN WORK FOR HiPER 2 In collaboration with groups from Italy, Spain, the UK, France and Poland we prepared the “Fusion Science Case and Design” section of the “HiPER Technical Background and Conceptual Design Report”, available in print and electronic versions at hiperlaser.org. This work was presented at the IFSA and APS conferences and will be published in a refereed journal in 2008. We also contributed to the successful preparatory phase proposal for the HiPER project (Figure 15.1). This 3 year preparatory phase should start in April 2008. We will lead the fast electron transport part of the fusion science work package. Figure 15.1 - Artists impression of the HiPER building. 15.3. ANALYSIS OF RESULTS FROM LASERSOLID EXPERIMENTS ON THE VULCAN PW 3 Analysis and numerical modeling of the HISAC results from 2005/6 was completed and an article has been prepared, which will be submitted at the beginning of 2008. Analysis of the results obtained from our Nov/Dec 2006 experiment is now well underway. Results from the K alpha imaging and the transverse probing have allowed us to infer the cone angle of the electrons accelerated into the target. Combined with previous results this clearly indicates that the cone angle increases with intensity and is unexpected result. This work has been accepted for independent of the spot diameter, a new and somewhat publication in Physical Review Letters. We have made a preliminary analysis of the results from the XUV imaging (Figure 15.2). The emission from all large area, plane solids is well characterized by a Gaussian, but the emission from 300 × 300 µm 2 plane solids has the same shape as the target and the result from the one successful shot with a 50 mg cm -3 silica aerogel target shows multiple, Gaussian peaks. This last result is particularly interesting, because it has been predicted that an electron beam in such lowdensity plasma should filament, but more detailed analysis and further experimental results are required. Figure 15.2 - A typical XUV image for a large area, plane solid target (top) and the XUV image for the aerogel target (bottom). 1 Activities performed in the frame of the Contract of Associated Laboratory, out of the Contract of Association EURATOM/IST, by CFP staff of the “Grupo de Lasers e Plasmas”. 2 Work developed in collaboration with S. Atzeni and A. Schiavi, Italy; J. J. Honrubia, Spain; X. Ribeyre, G. Schurtz, Ph. Nicolai and M. Olazabal-Loumé, France; C. Bellei and R. G. Evans, UK; J. Badziak, Poland. 3 Work developed in collaboration with M. Nakatsutsumi, Japan; J. S. Green and P. A. Norreys, Rutherford Appleton Laboratory, UK; T. Ma and F.N. Beg, University of California - San Diego, US. 72 We have analyzed the correlation of the size of the XUV spot in large area, plane solids with laser intensity, energy, pulse duration and spot diameter and with target thickness and areal density (thickness times density). This has shown that only the laser intensity and the areal density are determining factors. The spot size increases with increasing intensity and decreases with increasing areal density. The increase with intensity is consistent with an increase in cone angle with intensity, reinforcing our previous result. We are now investigating the physical mechanisms behind these correlations. 15.4. FILAMENTATION IN LASER ABLATION OF SOLIDS 4 As part of our program on X-ray lasers, an experiment to characterize plasma production by a line focused, 80 J, 300 ps iodine laser was carried out at the “Prague Asterix Laser System” (PALS). This revealed filamentary structures at densities well below critical, but a uniform plasma at higher densities. This suggested to us the presence of magnetic fields, so we modeled the experiments using a two-dimensional MHD code. This accurately reproduced the experimental observations, as a result of the magnetic field diffusing from the critical surface, where it is generated, into the lower density plasma where the thermal pressure was lower than the magnetic pressure, leading to instability, as illustrated in Figure 15.3. Figure 15.3 - The ratio of the magnetic pressure to the thermal pressure (shaded) and density contours at, from left to right, 1000, 100, 10, 1, 0.1, 0.01 and 0.005 times the critical density, after the laser interaction. We have derived a dispersion relation for density perturbations perpendicular to a temperature gradient and an existing magnetic field that reproduces the essential features of the numerical results. This would appear to explain a large number of experimental observations of density filaments in laser-solid experiments. It is also of importance to fast ignition inertial fusion, because it has been proposed to use a ~ 100 ps laser pulse roughly a ns before the main compression pulse to achieve a low adiabat compression. This work is being prepared for publication. A proposal for an experiment on PALS to measure the magnetic field has been accepted. 15.5. INTEGRATED NUMERICAL DESIGN OF LASER-PLASMA EXPERIMENTS 5 The high-power chirped pulse amplification (CPA) lasers, at Vulcan PW and at the “Laboratoire pour l'Utilisation des Lasers Intenses” (LULI) 2000, now have additional nanosecond beams, making it possible to carryout laserplasma rather than laser-solid experiments by pre-heating targets. This will greatly facilitate a direct comparison with theory, avoiding the complications of ionization, degenerate electrons and strongly coupled ions, which are irrelevant for many applications. Not only that, it will also be possible to obtain plasma targets with densities between those of a gas and a solid by pre-heating and homogenizing aerogel or foam targets, which are basically porous solids. The homogenization time of such targets has been found to be almost a nanosecond, so the results of experiments such as that shown in Figure 15.2 maybe significantly affected by the target structure. With these developments in mind we have started a numerical study of laser-plasma experiments, modeling the target pre-heating using a hydrocode, the PW interaction with the pre-heated target using a particle in cell (PIC) code and the transport of the electrons accelerated deep into the dense plasma by the PW laser using a hybrid code. Some preliminary results are given in Figures 15.4 and 15.5. Such experiments should be able to demonstrate the theoretically predicted transition from filamented to stable electron beam propagation with increasing plasma density and would provide an excellent test of our modeling capabilities. Figure 15.4 - 1D hydrocode results giving the target temperature as a function of space and time for (left) a 0.4 g cm -3 , 250 µ m wide CH target and (right) a 1 g cm -3 , 100 µ m wide CH target irradiated by a box pulse, with a rise time of 0.1 ns, a duration of 1 ns and an intensity of 5x10 13 W cm -2 . 4 Work developed in collaboration with B. Rus, Prague Asterix Laser System, Czech Republic. 5 Work developed in collabo ration with J. J. Ho n rubia, Spain 73 Figure 15.5 - PIC code results for the electron density (shaded) and laser electric field (contours) at the peak of the PW laser pulse. Left; 10 n cr , 50 µ m thick; Centre, 30 n cr , 50 µ m thick, Right; 30 n cr , 100 µ m thick, 45 ° angle of incidence. 81 16.5.2. THz characterization and generation 23 The search for relativistic mirrors in the optical domain is one of the challenges in new tunable and ultra-short coherent radiation sources from laser-plasma interactions. In order to create these relativistic mirrors we can interact electromagnetic waves with a relativistic ionization front. Focusing in vacuum an intense, short laser pulse on a highdensity gas jet will generate a relativistic front by optical field ionization along its propagation through the background gas. However, the difficulty of producing a total reflection relativistic mirror by the ionization front is the low cutoff frequency given by the relativistic factor of 1/r 2mirror , for the typical plasma densities. The current possibility of generating low frequency THz radiation sources produced by femtosecond laser pulses opens up the possibility of achieving the reflection conditions needed to obtain a relativistic mirror using ionization fronts. In order to investigate this approach, we assembled an experimental setup for producing and characterizing THz pulses at the laboratory “Terahertz to Optical Pulse Source” (TOPS) at the University of Strathclyde (Glasgow). The THz radiation was created using a photoantenna of GaAs. Applying a high-voltage and irradiating the surface of the semiconductor (GaAs) with the fs laser pulse makes it become conductive, accelerating the electrons and producing photons in the THz frequency region. The generation of these singlecycle THz pulses, triggered by the same laser driving the ionization front, allows us to fully collide the THz pulse with the counter-propagating ionization front. For the detection and characterization of the THz pulse two electro-optic techniques were used: spectral encoding and cross-correlation 25 . In both techniques, a THz and a chirped laser pulse are passed through an electro-optic crystal (ZnTe). The electric field of the THz pulse will change the refractive index of the crystal on one axis, inducing birefringence and changing the polarization of the chirped laser pulse. This way, the THz electric field leaves a “fingerprint” on the chirped laser pulse. The detection of this “fingerprint” is what differs in the two detection methods used. With the first one we obtain a time-to- frequency conversion, by impressing the temporal evolution onto the spectrum of the chirped beam, which is then measured by a spectrometer. The second one is a higher temporal resolution, single-shot method, which directly measures the amplitude of the encoded chirped pulse, by using a cross-correlation measurement technique upon a β-barium borate (BBO) crystal. The results of both methods reveal that the pulse duration is 500 fs and the central frequency is 0.2 THz (Figure 16.17). Figure 16.17 - THz time and frequency characterization. 16.6. DIAGNOSTICS 16.6.1. Single-beam interferometer and shadow diagnostic for laser-plasma interactions Two of the most common diagnostics in laser-plasma interactions are interferometry and shadowgraphy. With the interferograms one can calculate the density of the plasma, and shadowgrams allow us to obtain the precise shape of the plasma. Apart from the interferograms, common interferometric setups also allow one to obtain the shadowgrams produced by the plasmas. The problem with this kind of setups is that they normally rely upon two independent arms (one through the plasma and another as a reference) and it is only possible to use one diagnostic at a time. With this in mind, we developed a new compact single-beam interferometer that uses just one beam passing through the plasma, and thus was able to retrieve both interferometry and shadowgraphy simultaneously. As shown in Figure 16.18 the resulting images only show interference in half the beam aperture, allowing the remaining half, in one of the beams, to be used for obtaining the shadowgraphy. In order to obtain faster and better results in the laboratory, a program for acquiring data using digital or analog CCD cameras, with different interfaces, was developed (Figure 16.19). Several cameras are used for different types of diagnostic, such as interferometry and shadowgraphy. The objective of this program is to enable the use of several parallel cameras at the same time, in just one experimental setup, and this system has already been tested with success. To complement this program, a calculus platform was created to obtain important conclusions in real time. 23 Work developed in collaboration with G. Gallacher, J. Sun, C. Issac and A. Jaroszynski, University of Strathclyde (Glasgow), Scotland. 24 Jiang Z et al, Appl. Optics, 37, 8145-8146, (1998). 25 Jamison SP, Opt. Lett., 28, 1710-1712, (2003). 82 Figure 16.18 - Interferometer that delivers interferometry and shadowgraphy at the same time. Figure 16.19 - Data acquisition and calculus program developed. 16.6.2. Plasma refraction 26 The information that one can usually retrieve from a shadowgraphy diagnostic is limited to the plasma shape. Considering the refractive effects in the shadow image, a detailed analysis of the image formation can also enable us to obtain more information, such as an estimate of the plasma density and structure. A study of laser propagation through a plasma with a refractive index gradient has been performed, using a raytracing simulation program and mathematical software. A Gaussian density profile was simulated to understand physical phenomena. With careful analysis it can be concluded that the plasma acts as either a convergent or a divergent lens, depending on its density profile (Figure 16.20). Simulation results were compared with theoretical values 27 to pinpoint the focusing distance of the optical system, enabling the density profile of the plasma to be deduced. 16.6.3. Suite of diagnostics for high power laser pulses Owing to the need expressed by researchers performing high intensity laser-plasma experiments using the “Laboratório de Lasers Intensos” (L2I) laser to obtain systematic data about each laser shot, a permanent suite of diagnostics was installed before and after final pulse compression. Figure 16.20 - Plasma acting like divergent lens when crossed by coherent light source. The diagnostics include a calibrated photodiode for energy measurement, a near-field CCD camera for monitoring the beam profile before compression, a farfield CCD after the compressor for alignment stability and monitoring of focused beam profile, a radial shearing interferometer, and a second-order single-shot autocorrelator. The CCD images are obtained by imaging a leak through high-reflectivity mirrors. For the compressed pulse diagnostics, a tuneable fraction of the compressed beam is leaked through the turning mirror after the second grating and sent through a vacuum window and a removable beam elevator. The effects of compressed pulse propagation through this window and the subsequent air path were calculated in order to minimise the nonlinear distortions upon the probed pulse (Figure 16.21). Additionally, a 6-channel video switch and a LabViewbased image acquisition program developed in-house allow fast recording of any image, without the need for synchronised triggering. These additions, together with a set of new alignment references and monitoring, have allowed a considerable improvement in the efficiency of both the laser maintenance and the experiments. Figure 16.21 - Schematic view of diagnostics setup. RSI: radial shearing interferometer; VS: video switch; SSAC: single-shot autocorrelator. 26 Work developed in collaboration with C. Clayton, University of California – Los Angeles, US. 27 Behjar A et al, J. Phys. D: Appl. Phys. 30, 2872-2879 (1997). 83 16.7. HIGH-VOLTAGE PULSE GENERATOR 28 The previous experiments on plasma channel generation by high-voltage discharges, performed in 2006, allowed us to conclude that we could produce good quality plasma channels, but not with the required sub-ns jitter for precise laser pulse injection. This jitter was due to the nonreproducible way the plasma was initiated. In order to overcome this problem we decided to add a magnetic compressor to the system in order to provide a reproducible voltage in the device gap in the moment the discharge was initiated. This consists of a new section of coaxial transmission line added to the existent cable. The new schematic of the whole pulse generator can be seen on Figure 16.22. The pulse compressor is a 40 cm section of coaxial cable with ferrite toroidal cores (Ferroxcube ref. BD3/1/4S2), displaced around the inner conductor substituting part of the PTFE dielectric. This magnetic material needs to be biased with a DC current (37-80 A depending of the pulse voltage) before each shot. A robotic arm is used to apply this current safely between shots. Figure 16.22 - Scheme of the high-voltage pulse generator including the new magnetic compressor added to the 125 Ω transmission line. In Figure 16.23 we can see the oscilloscope traces produced in a typical shot with magnetic bias. The current rise-time (red) doesn’t follow the voltage rise (blue) due to the device inductance. The voltage rise-time shown in Figure 16.23 is ~ 5 ns, close to the limit of the oscilloscope bandwidth. Shorter rise-times can be achieved by extending the length of the magnetic compressor. However, the introduction of this compression section reduced the jitter to less than 1 ns our initial goal. Figure 16.23 - Voltage obtained by ddot signal integration (solid blue), and current measured using a pulse transformer (dashed red). 28 Work developed in collaboration with C. Clayton, University of California – Los Angeles – Electrical Engineering, US. 85 17. FUNDAMENTAL PHYSICS AND QUANTUM COMPUTING 1 L.O. Silva (Head), O. Bertolami (Deputy Head), T. Barreiro, C. Carvalho, A.M. Martins, J. Paramos, C. Bastos. 17.1. INTRODUCTION The work in this field has covered several topics, namely:  Pioneer anomalous acceleration;  Alternative models of gravity;  Dark energy and dark matter;  Putative violations of fundamental symmetries of nature;  Quantum computing. 17.2. PIONEER ANOMALOUS ACCELERATION The unexpected Doppler shift detected in the telemetry data of the Pioneer 10 and 11 spacecraft can be interpreted as an anomalous acceleration of the order of 8×10 -10 m/s 2 . The study of the potential systematic effects is being carried out by several groups throughout the world, but so far no concrete evidence has been found. This suggests that the anomalous acceleration might be a new physical effect; in this respect, many proposals have been advanced, from new gravity models to a new scalar field 2 . In 2007, our group participated in two proposals submitted in the context of the Cosmic Vision 2015 - 2025 call for missions of the European Space Agency (ESA), whose aim was to confirm and characterize the Pioneer anomaly. The main feature of the first proposal, Odyssey mission (Figures 17.1 and 17.2), is to incorporate in its payload a state of the art accelerometer to directly measure accelerations and contrast with Doppler shift readings. Beyond Jupiter, the main body of Odyssey launches a radio beacon experiment to carry on acceleration measurements and to extend the life of the mission. Figure 17.1 – Artistic impression of Odissey Figure 17.2 – View of Odissey The second proposal search for anomalous gravitation using atomic sensors (SAGAS), is based on measurements of gravitational fields, by comparison of the frequencies of a clock on board with clocks on Earth and on the International Space Station. The sensitivity and the expected life span of the mission would allow it to make relevant measurements of the gravitational field of the Kuiper belt, which in turn could help to sort out the nature of its structure 3 . In 2007, we have also carried out a study of the systematic effects affecting a hypothetic mission where accelerations would be measured through laser ranging of spheres launched by the mother spacecraft. 17.3. ALTERNATIVE MODELS OF GRAVITY Our study of alternative models for gravity has taken a new turn, by considering the possibility of directly coupling a function of the scalar curvature with the matter Lagrangian. This new coupling implies that the motion of a test particle is not geodesic, and opens the possibility of addressing the dark matter and Pioneer anomaly problems in the context of this new class of gravity theories. It is particularly interesting that our model presents features that are similar to some well discussed, but somewhat ad hoc and problematic, alternative gravity models, such as Modified Newtonian Dynamics (MOND) 4 . In the context of alternative gravity models, we have also considered the possibility of testing extensions of general relativity through the Galileo satellite constellation. 17.4. DARK ENERGY AND DARK MATTER In 2007, our work on dark energy and dark matter has focused on the detection of their interaction. We found that this interaction would affect the virial equilibrium of stationary clusters. The Abell cluster A586 (Figure 17.3), more than 30 galaxies, is particularly suitable for this study, as it is fairly spherical and shows no evidence of having undergone any process of merging for several 1 Activities performed in the frame of the Contract of Associated Laboratory, out of the Contract of Association EURATOM/IST, by CFP staff of the “Grupo de Lasers e Plasmas”. 2 Bertolami O and Páramos J, Class. Quant. Grav. 21, 3309-3321 (2004). 3 Bertolami O and Vieira P, Class. Quant. Grav. 23, 4625-4635 (2006). 4 Bertolami O and Páramos J, “Current tests of alternative gravity Theories: The Modified Newtonian Dynamics case”, Nov 2006. 12pp., Presented at 36 th COSPAR Scie ntific Assembly, Beijing, China, 16 - 23 Jul (2006), e - Print: gr - qc/0611025 . 86 composed by thousands of millions of years. Actually via the so-called Layzer-Irvine equation, that accounts for the interaction of dark matter and dark energy, we have found that the ratio between kinetic to potential energy densities is away from the expected -1/2 value at 1- sigma level. Furthermore, we found evidence that this interaction does affect the fall of dark matter into dark matter so that it differs, on cosmological scales, from the fall of baryons into baryons. This evidences a violation of the Equivalence Principle. Figure 15.3 – The massive strong-lensing cluster Abell586 In 2007, we have also considered models of dark energy and dark matter at a fundamental, quantum field theory level, in opposition to the fluid description considered in most of our work so far. We have studied, in particular, models where the dark energy field is a Standard Model singlet field and couples to the Higgs sector and to the neutrino sector. In the former case, we found that this coupling opens the possibility of indirect detection of the dark sector via its effect on the decay width of the Higgs field. This is particularly relevant as the detection of the Higgs field and the study of its decay modes is a top priority of LHC at CERN, which will start operating in a few months time. In what concerns the coupling with neutrinos, we have devised a perturbative approach that allows us to consistently treat the coupling of neutrinos with a large class of dark energy models. Our analysis shows that many of these models are free from instabilities, which were diagnosed due to an unsatisfactory treatment of the problem. 17.5. PUTATIVE VIOLATIONS OF FUNDAMENTAL SYMMETRIES OF NATURE In 2007, we have continued our work on the connection between the physics in the bulk 5-dimensional space and the one on our 4-dimensional brane. We have considered the question of spontaneous breaking of gauge symmetry and the issue of mass generation and localization on the brane. For that we considered a Higgs-like scalar field in the bulk, minimally coupled with a U(1) gauge vector field. Our results indicate that the process of spontaneous breaking of the gauge symmetry cannot account for the Standard Model symmetry breaking, as the bulk-brane mechanism we proposed is essentially gravitational. Nevertheless, we have shown that our mechanism is fairly interesting and effective in what concerns the localization of fields on the brane. Another line of research that we have opened up in 2007, was the suggestion that, in the context of string/M- theory vacua landscape, the various associate multiuniverses could actually interact among themselves. We have shown, in the context of a simplified model with two interacting universes, that the cosmological constant of one of the universes could be altered by the dynamics of the other universe. To account for the interaction between universes, we have advanced a new curvature principle. Interestingly, this curvature principle can also account for a suitable interpretation of the Generalized Second Law of Thermodynamics at a cosmological level. Finally, we have continued our study of noncommutative geometry phase space models. We have considered this more general noncommutativity in the cosmological context and studied the most likely initial conditions for a universe governed by this noncommutativity. This was achieved through the Wheeler-DeWitt equation for a Kantowski-Sachs geometry. We have shown, in opposition to the case of configuration space noncommutativity, that the wave function of the universe exhibits damping. This feature suggests that the choice of initial conditions in noncommutative phase space models can be done without any other additional principle. 17.6. QUANTUM COMPUTING In order to understand computation in a quantum context, it might be useful to introduce as many concepts as possible from the classical computation theory to the quantum case. One of these basic concepts concerns the functioning of finite quantum automata (QA) 5,6 . In this work we proposed a new model for a quantum automaton working with n-qubits and we addressed the question of minimizing it. The minimization of a QA is an important question not only because qubits are an expensive resource, but also because a deeper comprehension of any automaton starts always with its minimal-state equivalent automaton. 5 Kondacs A and Watrous J, Proceedings of the 38 th Annual Symposium on Foundations of Computer Science, 66-75 (1997). 6 Moore C and Crutchfield J, Theoretical Computer Science 237, 275-306 (2000). 87 The traditional approach to QA only considers pure states and represents them as unit vectors of a finite Hilbert space. In this work we generalized the usual description to mixed states, which are represented by density operators 7 . The problem of minimizing the dimension of the underlying Hilbert space was addressed using the partial trace operator. The two main results of this paper are: (i) The proof of a theorem for the existence of an equivalent QA. This theorem establishes a set of necessary and sufficient conditions in order that the dimension of the QA be reduced; (ii) an algorithm to find out the QA working with the least number of qubits. 7 Ahronov D, Kitaev A, and Nisan N, “Quantum circuits with mixed states”, arXiV:quantph/9806029. 89 18. ENVIRONMENTAL ENGINEERING PLASMA LABORATORY 1 C.M. Ferreira (Head), E. Tatarova (Principal Investigator), F.M. Dias, V. Guerra, J. Henriques, M. Pinheiro, E. Felizardo. 18.1. INTRODUCTION The research work in the Environmental Engineering Plasma Laboratory covered the following topics:  Plasma torches for environmental issues;  Extraordinary phenomena in hydrogen plasmas;  Improvement of plasma diagnostic techniques. 18.2. PLASMA TORCHES FOR ENVIRONMENTAL ISSUES 2 Having in view environmental issues, i.e. plasma sterilization and hazardous gases abatement, the main activity of the “Environmental Engineering Plasma Laboratory” (EEPL) during 2007 was focused on complex, experimental and theoretical investigations of microwave molecular plasmas over a large domain of operating conditions. Atmospheric pressure discharges are receiving growing interest due to their easy and low-cost operation for applications in a variety of plasma processing and manufacturing techniques that are currently performed in vacuum conditions. Many of the problems related with conventional plasma torches induced by DC or RF electric fields can be eliminated if a waveguide-based, atmospheric plasma torch driven by a surface-wave (SW) is used instead. One of the main advantages of such microwave discharges at atmospheric pressure is that they make it possible to inject large power densities into the plasma and thus achieve high population densities of active species. The complex work on microwave plasma torches and its applications for bacteria sterilization falls into the following main fields of investigation: (i) further improvement of the surfaguide based experimental set up (Figure 18.1); (ii) development of new experimental techniques for spectral and radio-physics diagnostics of molecular plasmas; (iii) development of a detailed theoretical model for the air plasma torch as a tool for optimization of the plasma source operation; (iv) microwave plasma based system for bacteria “killing”. The waveguide-surfatron based experimental setup has been further improved in order to ensure stable operation of the torch. The up grated experimental set-up is shown in Figure 18.1. Air and water are used as a working media. A new system for plasma dilution with water has been created and incorporated in the principal gas flow system. The new system provides gas flow rates from 100 to 2000 sccm under laminar gas flow conditions. The air plasma emission in the 250 − 850 nm range has been investigated. Emission spectroscopy has been used to detect the following emission lines: the 777.4 nm, 844.6 nm and 630 nm atomic oxygen lines, corresponding to the transitions O(3p 5 P→3s 5 S), O(3p 3 P→3s 3 S) and O(2p 1 D→2p 3 P), respectively, and the NO(γ) band in the range 230–260 nm (0–1, 0–2 and 0–3 vibrational transitions). The relative emission intensities of the Q1- branch of the OH[A2 Σ + → X2 Π] rotational band within the (0–0) vibrational transition (in the range 306–315 nm) have been used to determine the gas temperature. The experimental spectra have been compared with calculated ones to obtain the background gas temperature. Infrared sensitive measurements using an optical thermometer provided data about the wall temperature. The radio-physics methods have been applied to measure the wave number and SW attenuation coefficient. Amplitude and phase sensitive recording using electrical antennas provided axially resolved measurements of the wave dispersion characteristics. The so called “interferogram method”, based on the mixing of the traveling wave signal with a constant reference signal, has been further developed in order to be applied to the case of short plasma column lengths. A detailed self-consistent model for a microwave plasma torch, using air mixed with water as a working media, was developed. The system under analysis is a plasma source comprising a discharge sustained by an azimuthally symmetric SW mode and a post-discharge (see Figure 18.2). The system of equations considered to describe the plasma source includes: (i) Maxwell’s equations; (ii) the dispersion equation for the azimuthally symmetric TM surface mode; (iii) the rate balance equations for vibrationally excited states of electronic ground state molecules N 2 (X 1 Σ + g , ν); (iv) the rate balance equations for the excited states of molecules and atoms N 2 (A), N 2 (B), N 2 (a’), N 2 (a), N 2 (C), N 2 (a’’), N( 2 D), N( 2 P), O 2 (a), O 2 (b), O( 1 D), O( 1 S); the rate balance equations for ions and electrons N 2 + , N 4 + , O + , O 2 + , O 4 + , NO + , NO 2 + , H 2 O + , H 3 O + , H 2 + , H 3 + , HN 2 + , NH 3 + , NH 4 + , O - , O 2 - , O 3 - , H - , OH - , NO2 - , NO3 - ; the rate balance equations for groundstate molecules and atoms N, O, O 3 , NO, N 2 O, NO 2 , NO 3 , N 2 O 5 , H 2 O, H, H 2 , OH, HO 2 , H 2 O 2 , NH 3 , NH 2 , NH, HNO, HNO 2 , HNO 3 ; the gas thermal balance equation; the equation of mass conservation for the fluid as a whole. A big number of chemical and physical processes were taken into account. Those processes are: excitation and deactivation of electronically excited states of N, O, and H atoms, N 2 and O 2 molecules (88 processes); 211 chemical reactions of neutrals in electronic ground state; 63 1 Activities performed in the frame of the Contract of Associated Laboratory, out of the Contract of Association EURATOM/IST, by CFP staff of the “Grupo de Electrónica e Descargas em Gases”. 2 Work performed in collaboration with the Lebedev Physical Institute of Russian Academy of Sciences, Russia, the University of Sofia, Bulgaria, the Scientific Department of Shibaura Mechatronics Corp., Japan, and the Instituto Tecnológico de Aeronáutica, Brazil. 90 Magnetron Circulator H 2 O load stubs Waveguide-Surfatron Adjustable short-circuit Metallic tube Tubular extractor Outside Flow meters with shut-off valves “Nebulizer” High-voltage generator and magnetron controller Electric valve Electric valves Ar N 2 Valves To sewers To sewers High-Voltage Control cables Reflected power detector Metallic Table Gas cylinders Water Compress Air Quartz tube Plasma Magnetron Circulator H 2 O load stubs Waveguide-Surfatron Adjustable short-circuit Metallic tube Tubular extractor Outside Flow meters with shut-off valves “Nebulizer” High-voltage generator and magnetron controller Electric valve Electric valves Ar N 2 Valves To sewers To sewers High-Voltage Control cables Reflected power detector Metallic Table Gas cylinders Water Compress Air Quartz tube Plasma Figure 18.1 - Schematics of the experimental setup with the EEPL. reactions of neutrals with negative ions; 25 reactions between charged particles. The developed model provides a complex and detailed description of the entire plasma source, i.e. discharge and post-discharge zone. We have also calculated the relative intensities of O(777.4 nm) and O(844.6 nm) lines, and NO(γ) band due to excitation of O(3p 5 P), O(3p 3 P), and NO(A) states respectively. Model predictions have been experimentally validated. The present model constitutes an instrumental tool for optimization of plasma source operation. Figure 18.2 - Air plasma torch. The measured and calculated gas temperatures demonstrate a quite good agreement as shown in Figure 18.3. The gas temperature T g slightly varies around 3500 K along the main part of the plasma column, but it sharply drops to about 1000 K in the post-discharge zone (z > 3 cm). The length of the generated plasma torch is about 5 cm. There exists a significant radial gas temperature gradient since the difference between the axial gas temperature and the wall temperature is quite large (of about 3000 K). Thus, a strong radial variation of the collision rates and, consequently, of the species population densities is to be expected. 01234567 0 1000 2000 3000 4000 T g (theory) T wall -exp T g - exp Gas and wall temperatures (K) z (cm) To the launcher Figure 18.3 - Air plasma torch: gas and wall temperatures. The results for integrated intensities of the NO(γ) band, corresponding to (0–1, 0–2 and 0–3) vibrational transitions, as a function of the microwave power delivered to the launcher are presented in Figure 18.4. As it can be seen, the initial increasing in the line intensity is followed by a nonlinear saturation at microwave power greater than 350 W. The good agreement between theory and experiment confirms the hypothesis that the main channels for pumping of upper NO(A) state can be the E-E energy exchange in collisions involving NO(X) molecules and N2(A) metastables, according to the reaction N 2 (A) + NO(X)→ N 2 (X)+NO(A). The results clearly demonstrate that at higher temperatures the production of NO increases. 91 200 300 400 500 600 700 10 0 2x10 0 ∆ z=0.6 cm exp I [NO( γ )] theory I[NO( γ)] (a.u.) Power (W) Figure 18.4 - Air plasma torch: integrated intensities of the NO( γ ) band. Generation of “super hot” oxygen atoms in the air plasma torch has been detected. The measured fine structure profiles of the O(777.4 nm) line indicate that the O(3p 5 P) atoms generated in the air plasma torch are “super hot”, with a temperature of nearly 20000 K (Figure 18.5). This result can be readily explained keeping in mind that energies ∆E ~ 12.2 eV , 13.2 eV and 11.2 eV are available as a result of the ion-ion and electron-ion recombination processes O + + O − → O(3p 5 P) + O , O + + O 2 − → O(3p 5 P) + O 2 and N 2 O + + e → O(3p 5 P) + N 2 , respectively. The increase in the microwave power delivered to the plasma torch from 200 to 600 W leads to an increase in the kinetic temperature of the oxygen atoms, from about 15000 to 24000 K, as demonstrated by results obtained. Having in mind that oxygen atoms appear to be the main precursors for many decontamination processes, this air plasma torch can be regarded as an attractive source for plasma based environmental technologies. The results indicate that this torch produces an abundance of reactive atomic oxygen that could effectively oxidize biological agents and destroy hazardous molecules. 7770 7771 7772 7773 7774 7775 7776 7777 0 1000 2000 3000 4000 R 2 =0.998 R 2 =0.995 O (7775.39 Å) O (7774.17 Å) O (7771.94 Å) Q = 500 sccm ∆ z = 6 mm P = 610 W Intensity (a.u) Wavelength (Å) R 2 =0.998 Figure 18.5 - Fine structure line profiles of the O(3p 5 P → 3s 5 S) transition fitted with a Voigth function. A new experimental system has been created and applied for decontamination of biological agents. Figure 18.6 shows our first plasma sterilizer. Figure 18.6 - Plasma sterilizer. The active species come from a 2.45 GHz plasma torch operated within a 12 mm i.d. quartz tube. The microwave torch is situated on the top of the afterglow chamber made of Pyrex, as seen in the picture. The bacteria and its spores have been exposed in the post-discharge zone of the torch. A vertical lift platform directly below the plasma torch is used for the positioning of the sample placed inside a petri dish. The plasma effluent is directed downward towards the sample. Bacillus subtilis were chosen as the test biological agent to verify the efficacy of the created sterilizer. The preliminary experiments demonstrate high efficiency of air and water plasma torches to decontaminate the biological agents. 18.3. EXTRAORDINARY PHENOMENA IN HYDROGEN PLASMAS 3 Recently, puzzling observations have been made in hydrogen containing plasmas. For example, excessive broadening of the Balmer lines of atomic hydrogen has been observed in different types of discharges, which has been explained in terms of Doppler shift and broadening due to the acceleration of charges. However, many questions about the mechanism of “hot” hydrogen atom generation leading to large Balmer-lines broadening are presently open. The purpose of our investigation was to address these problems. Emission spectroscopy was used for the diagnostic of a large-scale, slot-antenna excited microwave plasma source operating in water vapor at low-pressure conditions. The Doppler temperatures corresponding to the broadening of the H β line at 486.1 nm (∼3000 K) are higher than the 3 Work performed in collaboration with the Eindhoven University of Technology, The Netherlands. 92 rotational temperatures (∼700 K) determined from the Q- branch of the Fulcher-α band [d 3 Π u (v=0) → a 3 Σ g + (v=0)]. The Doppler broadening of the O(777.4 nm) triplet line also indicates generation of “hot” oxygen atoms. Kinetic considerations demonstrate that electron-ion [H 3 O + + e → H 2 O + H hot *] and ion-ion [H 3 O + +OH - → H 2 O + H 2 + O hot *] recombination processes can be important sources of “hot” atoms in the far remote plasma zone, as can be seen from the results shown in Figure 18.7. 6563.5 6564.0 6564.5 6565.0 0.0 0.2 0.4 0.6 0.8 1.0 ∆ z = 20 cm ∆ z = 5 cm ∆ z = 1 cm Intensity (arb. units) λ [Α] p = 1 mbar P = 900 W φ = 162 Figure 18.7 - H α line profiles recorded at different axial distances in the remote plasma. An experimental study on the spectral broadening of the Balmer lines of atomic hydrogen has been performed in a He-H 2 , Ar-H 2 , H 2 and water microwave plasmas at low pressure conditions (p = 0.3 mbar). A conventional SW sustained microwave (2.45 GHz) discharge (cylindrical plasma column) has been used as a plasma source. The spectral profiles of H α , H β , H γ , H δ , H ε , H ζ , and H η lines, corresponding to the transitions H[(n=3– 9)→(n=2)] have been measured. The measured line profiles have been fitted by a Voigt function, which results from the convolution of a Gaussian profile (Doppler, instrumental and fine structure broadening) with a Lorentzian one (Stark broadening). A deconvolution procedure has been applied to determine the Doppler broadening and the corresponding temperature. The fine structure and instrumental broadening have been taken into consideration. As seen in Figure 18.8, an amazing result is observed. The temperature of hydrogen atoms increases with the increase in the upper level quantum number, i.e. the atoms at highest electronic levels are hotter. For example, the kinetic temperature of excited H(n = 8) atoms is about 5 times higher than for H(n=4) atoms. This weird behavior is observed in pure hydrogen, He-H 2 and water vapor plasma. To the best of our believe, this effect is definitely outside the framework of standard physics. 3 4 5 6 7 8 9 10 1000 2000 3000 4000 5000 Temperature (K) Upper level quantum number n He/H 2 (5%) He/H 2 (15%) He/H 2 (30%) He/H 2 (50%) He/H 2 (85%) He/H 2 (100%) Figure 18.8 - Dependence of the temperature on the upper level quantum number. 18.4. IMPROVEMENT OF PLASMA DIAGNOSTIC TECHNIQUES 18.4.1. Optical emission diagnostics 4 In order to improve analysis and processing of the measured emission lines, a new procedure to determine kinetic temperature of hydrogen atoms has been developed (Figure 18.9). Total Lorentz Width ∆λ L..total Measured Line profile Instr. Gauss Width ∆ λ G.instr Instr. Lorentz Width ∆λ L..instr Remaning Lorentz Width ∆λ reni Doppler (Gauss) Width ∆λ Doppler Relation between ∆λ f+D and ∆λ Doppler Total Gauss Width ∆λ G..total “fine structure + Doppler” Gauss Width ∆ λ f +D Volgtian fit Taking out instrumental funtion Taking out fine structure Figure 18.9 - The procedure for temperature determination. 4 Work performed in collaboration with the Eindhoven University of Technology, The Netherlands. 100 code SPARTAN for the identification of the main radiative species in the flow. A numerical rebuilding of the shockheated flows has also been carried out (Figure 19.9), which showed an adequate agreement with experimental results. (ii) A full reconstruction of the radiative flowfield around the EXOMARS entry vehicle will be carried using the SPARTAN code, following the method described in [28] 32 . This will allow predicting the values of the radiative heat fluxes impinging on the spacecraft heatshield, allowing a proper sizing of thermal protections. (iii) The NASA probe PHOENIX is scheduled to enter Mars atmosphere the 25 th May 2008. ESA plans to observe the entry phase of such a spacecraft utilizing the MARS EXPRESS spacecraft, currently in orbit around Mars. We are providing support to such a mission. Our task is to evaluate the radiative field that is likely to be observed during the entry phase of PHOENIX, and to advise on which will be the appropriate instrumentation of the MARS EXPRESS probe for properly measuring the atmospheric entry radiation of the PHOENIX probe 33 . 10−12 10−10 10−8 10−6 0 2000 4000 6000 8000 10000 12000 14000 16000 Time (s) Temperature (K) Time relaxation calculation with: • Rotational nonequilibrium (Tr?T) • vibrational nonequilibrium (Tv? T) • 3 vibrational temperatures for CO 2 • Losev CVD model • Losev&Park models for vibrational relaxation Figure 19.9 - Numerical rebuilding of the time-dependent relaxation processes behind a pure CO 2 shock-heated flow. We observe the quick equilibration of translational (dashed lines) and rotational (dashed-dotted lines) temperatures, followed by the equilibration with the CO 2 and O 2 vibrational temperatures (full lines) and finally the CO and C 2 temperatures. 32 Work performed in the frame of Fluid Gravity Eng./ESA Contract “Rebuilding of the radiative flowfield around EXOMARS”. 33 Work performed in the frame of ESA project “MARS EXPRESS support to the PHOENIX mission”. 101 20. MODELING OF PLASMA REACTORS 1 C.M. Ferreira (Head), L.L. Alves (Principal Investigator), R. Alvarez, L. Marques, C. Pintassilgo, S. Letout, J. Cruz, J. Gregório, J.S. Sousa. 20. 1. INTRODUCTION This project was focused on the modeling of different plasma sources, used in various applications (mainly with material processing and environmental control). The general goal was the development of sophisticated simulation tools describing the operation of these sources, in view of their optimization. The research work in this field studied the following devices: • Microwave-driven plasma reactor operated by an axial injection torch; • Micro-plasma reactors; • Capacitively coupled plasma reactors; • Inductively coupled plasma reactor; • Surface-wave plasma reactors. 20.2. MICROWAVE-DRIVEN PLASMA REACTOR OPERATED BY AN AXIAL INJECTION TORCH 2 We have continued the study of a microwave-driven (2.45 GHz) plasma reactor (cylindrical chamber with 55 mm radius and 150 mm height), operated by an Axial Injection Torch 3 (Figure 20.1), used for the destruction of industrial sub-products (VOC’s and BEXT aromatic hydrocarbons). The torch (connected to a coaxial waveguide with 5.3 mm and 14.5 mm inner and outer radii, respectively) creates atmospheric plasmas in different pure gases (argon, helium, nitrogen) or gas mixtures (e.g. air), over a wide range of powers (300−3000 W) and flow-rates (0.5−13 L min −1 ), producing very hot fluxes of plasma species (electron temperatures around 20000 K and gas temperatures between 2000−6000 K). Figure 20.1 - Plasma reactor operated by the AIT. We have started the development of a hydrodynamic model for the gas-plasma flowing system, yielding the distribution of mass density, pressure and (axial and radial) velocities, for a constant 1000 K gas temperature profile. The model solves the Navier-Stokes equations, which are discretized onto two-dimensional staggered cell-centered grids, by using a finite volume method based on surface integrals. The equations are solved using an algorithm SIMPLE, subject to the following boundary conditions: (i) symmetry conditions at reactor axis; no-slip conditions and flow conservation conditions for the velocity at reactor walls; (iii) imposition of the input gas flow at the nozzle’s tip; (iv) continuity condition for the velocity and closure condition for the pressure at the gas output opening. We have considered a 0.5mm nozzle’s radius and an output-to- input surface ratio of 100. Simulations were carried out in helium at atmospheric pressure, for input gas flows in the range 1000-10000 sccm. Simulation results captured the main features with the gas flow distribution (Figure 20.2), namely: (i) for a low input gas flow the neutral particles spread radially as they move towards the output, yielding a smooth recirculation of gas inside the reactor; (ii) for a high input gas flow the radial spread is considerably reduced, whereas a strong interaction with the upper wall modifies the recirculation pattern. 0 -1 -2 -3 -4 -5 -6 -7 -8 -9 Figure 20.2 - Distribution of the gas velocity (normalized to its maximum) inside the AIT-reactor system, for the following input gas flows (in sccm): 1000 (top), 10000 (down). 1 Activities performed in the frame of the Contract of Associated Laboratory, out of the Contract of Association EURATOM/IST, by CFP staff of the “Grupo de Electrónica e Descargas em Gases”. 2 Work supported by FCT (BPD/26420/2005) and Spanish MEC (Project CTQ2005-04974/PPQ), performed in collaboration with M.C. Quintero and A. Rodero, Departamento de Física, Universidad de Córdoba, Spain. 3 AIT, Spanish patents P200201328 and P200302980. 102 20.3. MICRO-PLASMA REACTORS 4 We have continued the study of atmospheric pressure micro-plasmas, created by electric discharges in very small geometries (100’s µm) without glow to arc transition, in view of developing portable devices for flue gas treatment, biological decontamination or detection of heavy metal gaseous traces, in ambient air or aerosols. 20.3.1. Micro-Cathode Sustained Discharge (MCSD) 5 We have started the systematic study of this device, which uses a micro-hollow cathode discharge (MHCD), running in oxygen and rare gas/oxygen mixtures at high power densities (up to 100 kW cm -3 ), to generate a downstream plasma (MCSD) with intense fluxes of O 2 (a 1 ∆) metastables and oxidative radicals (O, OH, O 3 ). MHCDs are created by applying a voltage between two closely spaced hollow electrodes separated by a thin dielectric layer. The MCSD is created between the MHCD cathode and a third positively-biased electrode, placed at a distance of some cm’s (Figure 20.3). Figure 20.3 - Schematics of the MHCD-MCSD experimental setup. We have characterized the MHCD-MCSD interaction using the current-voltage discharge response. The conditions for discharge ignition were established, as a function of the discharge voltage, pressure, flux, and composition. We have concluded that (i) the MCSD is a cold (<400 K) and low E/N (~15 Td) discharge region (similar to a positive column), which contrasts with the MHCD region characterized by very intense fields; (ii) the MHCD-MCSD mode transition is highly dependent on the presence of O 2 and discharge features are strongly influenced by the presence of (air and NO) impurities; (iii) the MHCD operating mode plays an important role on the MCSD ignition (in particular, it is possible to ignite the MCSD in a self-pulsed regime when the MHCD operates in the same regime, see Figure 20.4); (iv) the MCSD symmetry is highly affected by discharge flows above 100 sccm. We have also measured the gas temperature and the population of metastable O 2 (a 1 ∆), by using optical emission spectroscopy. We have started to develop a collisional-radiative model for oxygen plasmas, by setting up a very complete reaction scheme that accounts for the presence of positive ions O + , O 2+ , O 3+ and O 4+ , negative ions O – , O 2– , O 3– and O 4– , atoms O( 3 P), O( 1 D) and O( 1 S), vibrationally excited ground-state molecules O 2 (X 1 ,v=0–4), electronically excited molecules O 2 (a 1 ∆ g ), O 2 (b 1 Σ g+ ) and O 2 (C 3 ∆ u , A 3 Σ u+ , c 1 Σ u  ), and ozone O 3 . Figure 20.4 - MHCD-MCSD operating in a self-pulsed regime at 112 Torr pressure. 20.3.2. Microwave Micro-Plasma (MWMP) 6 We have initiated the study of an innovative plasma source for the production of atmospheric pressure micro-plasmas, in view of environmental applications. The device produces high-density (>10 15 cm -3 ), low-power (~10 W) plasmas in ambient air or in controlled environments (argon, xenon, nitrogen, oxygen, …), within the 100-300 µm end-gap of a microwave (2.45 GHz) strip-line, by using a continuous wave excitation (thus guaranteeing a steady-state discharge regime). We concluded the design and build of version-trial and version-1 with this device, which have successfully overcome the following problems: (i) discharge auto-ignition; (ii) microwave shielding; (iii) optimization of power coupling; (iv) docking of diagnostic systems. 4 Work performed in collaboration with V. Puech and C. Boisset-Laporte, Laboratoire de Physique des Gaz et des Plasmas, Orsay, and L. Pitchford, Laboratoire Plasmas et Conversion d’Énergie, Toulouse, France. 5 Work performed in the frame of the PhD thesis of J. Santos Sousa and supported by FCT (SFRH/BD/28668/2006). 6 Work performed in the frame of the PhD thesis of J. Gregório and supported by FCT (SFRH/29294/2006) and by Acordo Cooperação Científica e Técnica (GRICES / CNRS), 2006 –2008. 103 The MWMPs produced with this source in ambient air (Figure 20.5) were characterized by spatially-resolved emission spectroscopy measurements. By analyzing the nitrogen molecular spectra we have obtained vibrational temperatures in the range 4200-5000 K and rotational temperatures (hence gas temperatures) between 600 and 1800 K. The latter are maximum in the gap center and increase with the coupled power. We have also studied the device operation from the point of view of its electromagnetic coupling, with and without plasma, by measuring the reflected power. The optimum operating conditions were defined for a 50 µm gap and a 50 W input power, corresponding to a 60 mm length for the line transmission. These results agreed with simulation predictions obtained from commercial software (CST Microwave Studio TM ). This analysis was the starting point for the design of version-2 with the device, which will allow plasma ignition in a controlled atmosphere of argon and/or nitrogen. 3mm Figure 20.5 - Close-up over the MWMP produced in air at atmospheric pressure. Finally, we have started the development of a twodimensional stationary fluid code that solves the charged particle and the electron mean energy transport equations (for argon as a test gas), together with Poisson’s equation for the space-charge field and Maxwell’s equations for the electromagnetic excitation field. 20.4. CAPACITIVELY COUPLED PLASMA REACTORS 7 The study of low-pressure capacitively coupled radiofrequency (CCRF) discharges, produced within cylindrical parallel-plate reactors (~6 cm radius and ~3-5 cm height), was continued in hydrogen and initiated in nitrogen (see Figure 20.6). The focus was on the kinetic description of the plasma reactivity and the analysis of its influence upon charged particle dynamics. These studies used a hybrid calculation code, coupling a two-dimensional time-dependent fluid model (that solves the charged particle and the electron mean energy transport equations together with Poisson’s equation), the two-term homogeneous electron Boltzmann equation (yielding the electron energy distribution function in the presence of inelastic and superelastic collisional events, involving both electronically and vibrationally excited states), and quasi-homogeneous collisionalradiative models for the populations of the main excited species considered. Figure 20.6 - Close-up over the plasma chamber with a CCRF reactor, running a discharge in N 2 . Hydrogen CCRF discharges are routinely used in plasma assisted material processing applications, and particularly in the plasma enhanced chemical vapor deposition of hydrogenated microcrystalline silicon (µ- Si:H) thin films, from a precursor mixture of SiH 4 -H 2 , under high dilution conditions for silane. The increasing demand for higher throughput, larger processing areas, improved uniformity and film quality in the semiconductor industry justifies the investment in the characterization (both theoretical and experimental) of these discharges, in view of their optimization. Therefore, we have carried out a systematic characterization of CCRF hydrogen discharges produced over a wide range of applied voltages (50-600 V), frequencies (13.56-40.68 MHz), and pressures (0.2-1 Torr). Simulations have accounted for the presence of positive ions H + , H 2+ , and H 3+ , negative ions H − , electronically excited atoms H(n=1s,2s,2p,3–5), and vibrationally excited ground-state molecules H 2 (X 1 Σ g+ ,v=0–14). A good quantitative agreement was found between simulations and experiment for the coupled electrical power and the plasma potential. The model underestimates the values of the electron density, the self-bias potential, and the H(n=1) atom density with respect to measurements, but agrees with experiment when predicting that all these parameters increase with either the applied voltage, the frequency or the pressure, thus confirming that the production of atomic species proceeds mainly via electron collisions. The dissociation degree was about 10 −3 for the work conditions considered. The quality 7 Work performed in collaboration with J. Jolly, École Polytechnique, Palaiseau, and G. Cernogora, Service d’Aéronomie, Vérrières, France. 104 of simulations for the density of H atoms (Figure 20.7) was strongly related to the use of a wall recombination probability for this species that was experimentally measured, thus accounting for surface modification with discharge operating conditions. Results evidenced the key role played by the atomic wall recombination mechanism in plasma description. 0 100 200 300 400 500 10 13 10 14 p = 0.5 Torr Simulations x4 13.56 MHz 27.12 MHz 40.68 MHz n H (cm -3 ) V rf (V) 0.2 0.4 0.6 0.8 1.0 10 14 W = 30W Simulations x3 13.56 MHz 27.12 MHz 40.68 MHz n H (cm -3 ) p (Torr) Figure 20.7 - Calculated H atom density for a CCRF discharge, as a function of the applied voltage (top) and pressure (down). The study of CCRF discharges in nitrogen / methane mixtures (for CH 4 concentrations up to 2%) can be used to simulate the atmosphere of Titan, at laboratory scale. In the past, these discharges have already been successfully used to produce, in gas phase, dust particles analogues to Titan’s aerosols-tholins. Therefore, we have started the study of CCRF discharges (13.56 MHz) produced in pure nitrogen, at 0.1-2 Torr pressures and 10-50 W coupled powers. Simulations have considered the presence of positive ions N 2+ and N 4+ , vibrationally excited groundstate molecules N 2 (X 1 Σ g+ ,v=0–45), and 7 electronically excited states of the N 2 molecule, accounting for the production of electrons via associative ionization mechanisms involving the N 2 (A) and N 2 (a’) metastables. First results reveal that the 2D profile of the electron density exhibits an unexpected torsion effect (Figure 20.8), due to the spatial asymmetry in the profiles of the metastable species. 0 4 0 2 4 0.00 0.05 0.10 0.15 r (cm) RF electrode z (cm) n e (10 10 cm -3 ) Figure 20.8 - Time-average spatial profile of the electron density for the CCRF discharge, at 250V applied voltage and 0.4Torr pressure. 20.5. INDUCTIVELY COUPLED PLASMA REACTOR 8 We have pursued the modeling of a radio-frequency (13.56 MHz) inductively coupled plasma (ICP) reactor 9 , used as an ion source for ion milling applications or the oxidation of thin films. Usually, the ICP-reactor operates in Ar and Ar/O 2 mixtures at very low pressure (~ 0.1 mTorr) and high plasma densities (~ 10 11 -10 12 cm -3 ), under the action of a static magnetic field of ~ 400-800 Gauss, to ensure both a high creation rate of species and a reduced contamination. The discharge is produced by applying a rfcurrent of ~ 1 A to a 6-turn planar coil (52.5 mm radius), near the dielectric window (Figure 20.9) of a cylindrical metallic chamber (97.5 mm radius and 100 mm height). Ion extraction is achieved through a set of metal grids, which can be polarized yielding a maximum voltage drop of 1 kV. Figure 20.9 - Dielectric window of the ICP-reactor with the ion beam system. 8 Work performed in the frame of the MsC thesis of J. Cruz, in collaboration with S. Cardoso and P. Freitas, Instituto de Engenharia de Sistemas e Computadores - Microsistemas e Nanotecnologias (INESC-MN), Lisbon, Portugal. 9 Nordiko - 3000 reactor at INESC - MN. 105 The two-dimensional model includes an electromagnetic module (that solves Maxwell’s equations, given the applied current and the plasma-induced current density), and a hybrid calculation code including a stationary fluid module (that solves the charged particle and the electron mean energy transport equations together with Poisson’s equation, given the electromagnetic field distribution), and the two-term homogeneous electron Boltzmann equation (yielding the electron energy distribution function, and thus all the corresponding transport parameters and rate coefficients). Boundary conditions for the electromagnetic module include an analytical expression for the electric field profile, produced by a distribution of circular current rings (including the contribution of both the plasma and the rf antenna) at the dielectric window. The fluid module considers flux boundary conditions at the reactor walls for both particle and mean energy, accounting for a partial transparency at the extraction grids. After discretization, the electromagnetic equations are solved using a Gauss- Seidel method (with alternate column- and row-wise iterations), whereas the transport equations are solved using a time relaxation algorithm with an ADI method. This preliminary model version was solved for argon neglecting the presence of the static magnetic field, but considering a gas pressure of 500 mTorr as to ensure plasma confinement. Simulations for 0.8-1.5 A rf-currents, considering a single grounded grid with 50% transparency, yielded coupled powers of 27-95 W and an ion extraction current of 5 mA (Figure 20.10). Figure 20.10 - Time-average spatial profile of the electron density in the ICP-reactor, at 1.5A rf-current and 0.5Torr pressure. 20.6. SURFACE-WAVE PLASMA REACTORS 10 Nitrogen and nitrogen-mixture plasmas are increasingly used for plasma-assisted processing applications, such as the modification and functionalization of materials like polyethylene terephthalate (PET), low-density polyethylene (LDPE), nanotubes, polymer surfaces used in the biomedical field in view of improving their biocompatibility, and for the deposition of N 2 containing functional groups in textiles, among others. In these applications the dissociating and ionizing properties of these plasmas are used to produce large fluxes of radicals with a high chemical reactivity, at ambient temperature and low pressure (< 1 Torr). By combining the reactivity of nitrogen plasmas with the versatility of surface-wave driven discharges (2.45 GHz) we obtain a formidable engineering tool for the tailoring of materials. We have started to adapt and update a simulation code for the description of such discharges, with cylindrical geometry, by coupling a homogeneous kinetic model for N 2 (including the rate balance equations for 45 vibrationally excited levels of the ground-state molecule and 10 electronically excited atomic and molecular species) with a one-dimensional hybrid calculation code including a stationary fluid module (that solves the charged particle and the electron mean energy transport equations, together with Poisson’s equation for the space-charge field and Maxwell’s equations for the TM 00 surface-wave mode) and the two-term homogeneous electron Boltzmann equation (to self-consistently calculated the electron transport parameters and rate coefficients). 10 Work performed in collaboration with J. Cotrino, Instituto de Ciencias de Materiales de Sevilla, Spain. 107 21. PLASMA AND ELECTROMAGNETIC PROPULSION 1 C.M. Ferreira (Head), M.J. Pinheiro (Principal Investigator), A.A. Martins. 21.1. INTRODUCTION The research work in this field covered the following topics: • Plasma propulsion; • Electromagnetic propulsion; • Research on fundamental problems of plasma physics; • Analytical glow discharge optical emission spectroscopy. 21.2. PLASMA PROPULSION There has been a growing interest in the field of plasma aerodynamics related to its outstanding importance in active flow control, overriding the use of mechanical flaps. The plasma created above a blunt body was shown to modify the laminar-turbulent transition inside the boundary layer, to induce or reduce the fluid separation, reducing drag, allowing sonic boom minimization schemes and avoiding unwanted vibrations or noise 2 . To achieve a better understanding of the mechanism responsible for the boundary layer control and propulsions of neutrals we developed (and are still improving) in our laboratory a self-consistent two-dimensional model of the temporal and spatial development of the OAUGDP TM. . The plasma actuator simulation domain is a 2D Cartesian geometry with total length L x =4 mm, along the Ox-axis, and height L y =4 mm. It consists of conductive copper strips (with negligible thickness) of 1 mm width, separated by a 0.065 cm thick dielectric with 3 mm width and relative permitivitty ε r  Figure 21.1 shows a schematics of the device. The capacity of the reactor is given by the conventional formula C=ε 0 ε r /d. The working gas is an "air-like" mixture of a fixed fraction of nitrogen ([N 2 ]/N=0.78) and oxygen ([O 2 ]/N=0.22), as is normally present at sea level at p=1 atm. The electron homogeneous Boltzmann equation is solved with the two-term expansion in spherical harmonics, using the cross sections set of excitations by electron impact taken from Siglo Data Base. Rates coefficients and transport parameters are so obtained. The chemistry included in the model is the most relevant at atmospheric pressure, and it considers the following species: N 4 + , N 2 + , O 2 + , O 2 - and electrons. The reactions included in the present kinetic model are given in Ref 3 . Figure 21.2 shows the evolution, along a full period, of the calculated electric current, applied voltage, gas voltage and memory voltage. Figure 21.1 - Schematics of the device OAUGDP TM . 0 50 100 150 200 -3 -2 -1 0 1 2 3 Current (A) Time ( µ s) -8000 -6000 -4000 -2000 0 2000 4000 6000 8000 V m V g V Figure 21.2 - Electric current, applied voltage, gas voltage and memory voltage as a function of time, at V rms =5 kV, f =5 kHz and for a 3 mm dielectric width. Solid curve, current; dotted curve, V m ; dashed-dot curve, V g ; dashed curve, V. With the assumed conditions at about 740 Volts electron avalanches develop, replenishing the volume above the surface with charged particles. Hence, the charged particles flowing to the dielectric surface start accumulating on the surface, building-up an electric field that prevents the occurrence of a high current, and therefore quenching the discharge development at an early stage. Figure 21.3 shows the electric field profile at a given 1 Activities performed in the frame of the Contract of Associated Laboratory, out of the Contract of Association EURATOM/IST, by CFP staff of the “Grupo de Electrónica e Descargas em Gases”. 2 Enloe CL, McLaughlin TE, VanDyken RD, Kachner KD, Jumper EJ, and Corke TC, AIAA Journal 42(3), 589 (2004). 3 Pinheiro MJ, Plasma Process Polym. 3, 135 (2006). 108 0 ,0 8 0 ,1 6 0 , 0 8 0 ,1 6 0 1 x 1 0 6 2 x 1 0 6 3 x 1 0 6 4 x 1 0 6 5 x 1 0 6 Electric Field V/cm) X (cm) Y (cm) Figure 21.3 - Electric field distribution in the X-Y plane, at a given time during the first-half cycle, for the conditions of Figure 21.2. time above the anode. Note the peak at the interface of the dielectric with the electrode. Figure 21.4 portrays the arrival of electrons at the anode at t = 6 µs. The body forces are calculate using ( ) EnneF e i r r −= and are given in Figure 21.5. They strongly depend on the number of streamers occurring during both cycles, but there is a general tendency for asymmetry, being more negative during the second half-cycle. This explains why the gas speed tends to invert between both half-cycles, one feature which reduces the performance of this device in what gas speed is concerned. 0,08 0,16 0,24 0,32 0,40 0,08 0,16 0,24 0,32 0,40 10 5 10 6 10 7 10 8 10 9 10 10 10 11 10 12 10 13 t=6.0 µs Electron Density (#/cm 3 ) Y (cm) X (cm) Figure 21.4 - Electron density at t=6 µ s, for the conditions of Figure 21.2. This event portrays the arrival of electrons to the positive electrode. 0 50 100 150 200 -1,0 -0,5 0,0 0,5 1,0 F x F y Body forces (N/m) time ( µ s) Figure 21.5 - Body forces in vs. time, showing the x-component (responsible for the neutral gas acceleration) and the ycomponent (responsible for the boundary layer control). Same conditions as in Figure 21.2. 21.3. ELECTROMAGNETIC PROPULSION There is a growing interest in academia and industry on electromagnetic thrusters as a source of propulsion and energy. This quest might revolutionize space exploration and energetic in the near-future. This is the reason why, in parallel to our research in conventional atmospheric plasmas, we develop some effort to research along this direction, starting by clarifying some methodological difficulties related to the fundamental set of Maxwell’s equations. These include a modification and clarification of Faraday's law of induction in vacuum, using the procedure described in 4 , which embeds the Lorentz force into the formulation. The result is in complete agreement with the actual set of Maxwell's equations for bodies at rest, the only novel feature is the introduction of a new kind of electromotive force. Examining the problem of a moving circuit with this procedure, it is shown that a new force of induction should act on a circuit moving through an inhomogeneous vector potential field. This overlooked induction force is related to the Aharonov-Bohm effect, but can also be related to the classical electromagnetic field when an external magnetic field is acting on the system. Technological issues are being studied by us, needing an experimental approach in the near-future. Along other line of research 5 , the inertia property of matter is discussed in terms of a type of induction law related to the extended charged particle's own vector potential. Our approach is based on the Lagrangian formalism of canonical momentum. By writing Newton's second law in terms of the vector potential a development in terms of retarded potentials is obtained, which allows for an intuitive physical interpretation of its main terms. 4 Pinheiro MJ, Physics Essays 20(2) to appear (2007). 5 Martins AA and Pinheiro MJ, AIP Conf. Proc. 880, 1189 (2007). 6 Pinheiro MJ, Space Technology International Forum (STAIF-2007), oral report, Albuquerque NM, USA, February 2007. 7 Fermi E, Nuovo Cimento 25 , 159 (1923). 109 This framework provides a clear physical insight on the physics of inertia. It is shown that the electron mass has a complete electromagnetic origin and the covariant equation obtained contributes to clarify the “4/3 mass paradox”. This understanding broadens the possibility to manipulate inertial mass and suggests some mechanisms for possible applications of electromagnetic propulsion and the development of advanced space propulsion physics. Those findings enabled us to suggest the electromagnetic origin of inertia and mass 6 . Similar conclusion was sustained by E. Fermi 7 , although he arrives to the same conclusion through a different approach. 21.4. RESEARCH ON FUNDAMENTAL PROBLEMS OF PLASMA PHYSICS Plasma-wall interactions play a major role in plasma physics. Its complexity, however, continue to elude us when the aim is the complete description of a magnetized non-isothermal plasma transport, in a conducting vessel. Initially, the origin of the anomalous diffusion was assumed to be due to the turbulence of small-scale instabilities. Rather than attempting to solve this complex problem, our work proposes another possible (“circuital”) mechanism for wall current drain, which considers the effect of the magnetic field flux “cutting” particles trajectories 8 . This model is expected to be valid in the regime where the cyclotron frequency Ω c is much larger than the collision frequency ν c . We obtained an analytical expression for the anomalous diffusion coefficient. Figure 21.6 compares two numerical results to our theoretical prediction (the unit 1 Hx = 10 -27 T m 3 is used for the B/N ratio). The data was obtained via Monte Carlo simulations of electron transport in crossed electric and magnetic fields 9 , while the theoretical prediction was given by our analytical equation. Full agreement with the numerical calculations is not obtained, because (i) we have neglected effects related to time variations of the electromagnetic field, and (ii) we assumed that the plasma is collisionless. This explains the large discrepancy for the diffusion coefficient above 1000 Hx, when the very important effect of collisions randomizes individual trajectories, and our approach is no longer valid. We have reviewed different models of the electric field reversal in glow discharges, including our “dielectric-like model” 10 . The field inversion occurs at the interface between the plasma sheath and the beginning of the Figure 21.6 - The diffusion coefficient as a function of phase in a sinusoidal electromagnetic field. The two numerical results (at 5000 Hx and 1000 Hx) were obtained with Monte Carlo simulations of electron transport in an argon plasma, subject to crossed electric and magnetic fields. The theoretical prediction ('theo') is given by our analytical equation. The dashed line indicates the amplitude of the external magnetic field. Other parameters used for these data are as follows: f=100 MHz; Ωc ≈ 1010 Hz; kT/e=5.4 eV; p=1 Torr, Tg=300 K. negative glow. Fundamental properties relate to field inversion phenomena in the frame of a dielectric model. A simple analytical dependence is obtained for the axial location of the field reversal, in terms of macroscopic parameters. In addition, we have obtained the magnitude of the minimum electric field inside the trap, the trapping well length, and the trapping time of the slow electrons into the well. We have emphasized the description of the dielectric behavior, thus not contemplating plasma chemistry and plasma-surface interactions. The analytical results obtained can be useful for hybrid fluid-particle models, since simple criteria can be applied to accurately remove electrons from simulations. 21.5. ANALYTICAL GLOW DISCHARGE OPTICAL EMISSION SPECTROSCOPY 11 Glow discharge optical emission spectroscopy is a widely used method for quantitative analysis of materials composition. The method makes possible to investigate metals, polymers, glasses and ceramics. This work aimed to determine the effect of molecular gases on analytical glow discharges 12 . 8 Pinheiro MJ, J. Phys. Conf. Ser. 71, 102002 (2007) and references therein. 9 Raspopovic ZM, Dujko S, Makabe T, and Petrovic Z Lj, Plasma Sources Sci. Technol. 14, 293 (2005). 10 Pinheiro MJ, Gas Discharges-Fundamentals and Applications, (J. Amorim Filho ed.), Research SignPost, Trivandrum, India, 2007. 11 Work performed in the frame of project “Electron kinetics in gas mixtures used for Analytical Glow Discharge Optical Emission Spectroscopy” (GRICES/ITCP), in collaboration with the Research Institute for Solid State Physics and Optics, Hungary and the Instituto Tecnológico Nuclear, Portugal. 12 Pinhão N, Pinheiro MJ, and Donko Z, 60 th GEC, Arlington, Virginia, USA, October 2007. 111 22. PUBLICATIONS, LABORATORIAL PROTOTYPES, PRIZES AND AWARDS 22.1. MAGNETIC FUSION 22.1.1. Publications in Books • Varandas C, “Perspectivas das tecnologias nucleares para a produção de energia”, Energia e desenvolvimento sustentável, edição da Associação de Amizade Portugal/EUA, 127, 2007. • Varandas C and F Serra “Nuclear fusion: an energy for the future”, in ‘A portrait of state-of-the art research at the Technical University of Lisbon, 163, Springer, Netherlands, 2007. 22.1.2. Publications in refereed scientific journals (publications in ISI) • Angioni C, R Dux, E Fable, AG Peeters and the ASDEX Upgrade Team, “Non-adiabatic passing electron response and outward impurity convection in gyrokinetic calculations of impurity transport in ASDEX Upgrade plasmas”, Plasma Physics and Controlled Fusion, 49, 12, 2027, 2007. • Angioni C, H Weisen, OJWF Kardaun, M Maslov, A Zabolotsky, C Fuchs, L Garzotti, C Giroud, B. Kurzan, P Mantica, AG Peeters, J Stober and the ASDEX Upgrade Team and EFDA-JET contributor, “Scaling of density peaking in H- mode plasmas based on a combined database of AUG and JET observations”, Nuclear Fusion, 47, 9, 1326, 2007. • Asp E, J Weiland, X Garbet, V Parail, P Strand and JET EFDA contributers, “Critical gradient response of the Weiland model”, Plasma Physics and Controlled Fusion, 49, 8, 1221, 2007. • Behn R, A Alfier, S Yu Medvedev, Ge Zhuang, R Pasqualotto, P Nielsen, Y Martin and the TCV Team, “Edge profiles of electron temperature and density during ELMy H-mode in ohmically heated TCV plasmas”, Nuclear Fusion 49, 8, 1289, 2007. • Bizarro JPS, X Litaudon, TJJ Tala, and JET EFDA contributors, “Controlling the internal transport barrier oscillations in high performance tokamak plasmas with a dominant fraction of bootstrap current”, Nuclear Fusion (Letters Section) 48, L41-L45, 2007. • Bizarro JPS, “On the behavior of the continuous-time spectrogram for arbitrarily narrow windows”, IEEE Transactions on Signal Processing 55, 1793-1802, 4335, 2007. • Buttery RJ, A Loarte, PJ Lomas, P Mantica, DC MacDonald, S Saarelma, R Sartori, G Saibena and JET EFDA contributers, “Progress towards an integrated solution for the ITER baseline scenario based on high current and highly shaped plasma operation at JET”, Plasma Physics and Controlled Fusion, 49, 5A, A59, 2007. • Camenen Y, A Pochelon, R Behn, A Bottino, A Bortolon, S Coda, A Karpushov, O Sauter, G Zhuang and the TCV Team, “Impact of plasma triangularity and collisionality on electron heat transport in TCV L-mode plasmas”, Nuclear Fusion, 47, 7, 510, 2007. • Cannas B, A Fanni, P Sonato, MK Zedda and JET-EFDA contributors, “A prediction tool for real-time application in the disruption protection system at JET”, Nuclear Fusion, 47, 11, 1559, 2007. • Chapman IT, SD Pinches, JP Graves, RJ Akers, LC Appel, RV Budny, S Coda, NJ Conway, M de Bock, L-G Eriksson, RJ Hastie, TC Hender, GTA Huysmans, T Johnson, HR Koslowski, A Krämer-Flecken, M Lennholm, Y Liang, S Saarelma, SE Sharapov, I Voitsekhovitch and the MAST and TEXTOR Teams and JET EFDA Contributors, “The physics of sawtooth stabilization”, Plasma Physics and Controlled Fusion, 49, B12, B385, 2007. • Chapman IT, TC Hender, and JET EFDA Contributors, “Perturbation of tokamak magnetic surfaces by applied toroidally asymmetric magnetic fields”, Nuclear Fusion, 47, 11, L36, 2007. • Coda S, E Asp, E Fable, TP Goodman, O Sauter, VS Udintsev, R Behn, MA Henderson, A Marinoni, GP Turri, C Zucca and the TCV Team, “The physics of electron internal transport barriers in the TCV tokamak”, Nuclear Fusion, 47, 7, 714, 2007. • Coelho R, E Lazzaro, “Effect of sheared equilibrium plasma rotation on the classical tearing mode in a cylindrical geometry”, Physics of Plasmas, 14, 1, 12101, 2007. • Coelho R, “Nonlinear growth of marginally unstable tearing modes”, Physics of Plasmas, 14, 052302, 2007. • Colas L, A Ekedahl, M Goniche, JP Gunn, B Nold, Y Corre, V Bobkov, R Dux, F Braun, J-M Noterdaeme, M-L Mayoral, S Heuraux, E Faudot, J Ongena and ASDEX Upgrade and JET-EFDA contributors, “Understanding the spatial structure of RF-induced SOL modifications”, Plasma Physics and Controlled Fusion, 49, 12B, B35, 2007. • Donné AJH, AE Costley, R Barnsley, H Bindslev, R Boivin, G Conway, R Fisher, R Giannella, H Hartfuss, MG von Hellermann, E Hodgson, LC Ingesson, K Itami, D Johnson, Y Kawano, T Kondoh, A Krasilnikov, Y Kusama, A Litnovsky, P Lotte, P Nielsen, T Nishitani, F Orsitto, BJ Peterson, G Razdobarin, J Sanchez, M Sasao, T Sugie, G Vayakis, V Voitsenya, K Vukolov, C Walker, K Young and the ITPA Topical Group on Diagnostics, “Diagnostics”, Nuclear Fusion, 47, 6, S337, 2007. 118 "Experiments on FTU with a liquid lithium limiter", ECA Vol.31F, O-2.001 (2007). • Nabais F, D Borba, M Garcia-Muñoz, T Johnson, V Kiptily, M Reich, MFF Nave, SD Pinches, P Sandquist and S Sharapov, “Redistribution of ICRH Fast Ions in the Presence of Fishbones and Alfvén Eigenmodes”. • Nave MFF, LG Eriksson, T Hellsten, K-D Zastrow, B Alper, Y Andrew, R Barnsley, J Brzozowski, K Crombé, A Czarnecka, M von Hellermann, J Ongena and JET EFDA contributors, “Toroidal Rotation in Ohmic and RF heated Plasmas”. • Petrzilka V, J Maillou, M Goniche, K Rantamäki, G Corrigan, V Parail, P Belo, A Ekedahl, K Erents, P Jacquet, K Kirov, J Ongena, J Spence and JET EFDA contributors, “Near LH Grill Density Variations as a Function of Gas Puff and LH power”. • Ribeiro T, B Scott and F Serra, "Self consistent MHD equilibrium in turbulence simulations”. • Sandquist P, SE Sharapov, M Lisak, T Johnson and F Nabais, “Fast ion anisotropy drive for bi-directional tornado modes on JET”. • Udintsev VS, E Asp, O Sauter, H Shidara, F Turco, G Turri, S Coda, G Falchetto, TP Goodman, X Llobet, TI Madeira, Ph Marmillod, H Weisen, “Control of the oscillatrory regime by local current perturbation in ECCD plasmas on TCV” Società Italiana di Fisica, Pisa (Italy), 18 th September 2007 • Cesario R, C Castaldo, A Fonseca, V Parail, P Smeulders, M Beurskens, “Esperimenti di barriera interna di trasporto in plasmi ad alta triangolariti del JET (Joint European Torus) con impiego di lower hybrid current drive (LHCD)”. International Workshop on Burning Plasma Diagnostics, Villa Monastero, Varenna, Italy, 24-28 September 2007 • Coelho R, D Alves and JET EFDA contributors, “Real-time magnetic field pitch angle estimation with a motional stark effect diagnostic using Kalman filtering”. • Madeira TI, P Amorim, BP Duval, CAF Varandas, “High throughput pulse height analysis diagnostic for hot burning plasmas” 11 th IAEA Technical Meeting on H-mode Physics and Transport Barriers, Tsukuba, Japan, 26 th September 2007 • McDonald DC, C Giroud, L Laborde, C Petty, B Alper, M Brix, R Buttery, E de la Luna, A Fonseca, N Hawkes, J Hobirk, D Howell, S Jachmich, E Joffrin, R Koslowski, H Leggate, I Nunes, C Perez Von Thun, I Voitsekhovitch, and JET EFDA contributors, Collisionality and beta dependence of confinement in JET ELMy H-modes. 10 th IAEA Technical Meeting on Energetic Particles in Magnetic Confinement Systems, 8-10 October 2007, Kloster Seeon, Germany • Pinches SD, N Arcis, HL Berk, DN Borba, I Chapman, A Fasoli, S Hacquin, A Klein, F Nabais, M Reich, SE Sharapov, D Testa, V Kiptily, “Fast Ion Driven Instabilities in JET”. • Plyusnin VV, B Alper, E de La Luna and JET EFDA contributors, “Analysis of non-thermal features of electron cyclotron emission measured during ELMs in JET”. International Conference on Research and Applications of Plasmas, 16-19 October 2007 • Carvalho PJ, H Thomsen, S Gori, U Toussaint, J Geiger, A Weller, R Coelho and H Fernandes, “Comparison of fast tomographic methods for application on the Soft X-Ray Tomography System on Wendelstein 7-X Stellarator”. 17 th Technical Meeting on Research Using Small Fusion Devices, Lisbon, 22-24 October 2007 • Alonso MP, JH Severo, FO Borges, JI Elizondo, LA Berni, M Machida, CAF Varandas, RMO Galvão, “Multipoint Thomson scattering diagnostic for the TCABR tokamak with centimeter spatial resolution”. • Carvalho PJ, H Thomsen, S Gori, U Toussaint, A Weller, R Coelho, A Neto, T Pereira, C Silva and H Fernandes, "Fast tomographic methods on the tokamak ISTTOK". • Coelho R, D Alves and C Silva, “Time scale analysis of ISTTOK probe data”. • Duarte AS, J Santos, H Fernandes, A Neto, T Pereira, CAF Varandas, "FireCalc: an XML-based Framework for Distributed Data Analysis". • Figueiredo J, RB Gomes, H Fernandes, A Sharakovski, “Plasma Spectroscopy in ISTTOK”. • Lunt T, C Silva, H Fernandes, C Hidalgo, MA Pedrosa, P Duarte, H Figueiredo and T Pereira, "Edge plasma pressure measurements using a mechanical force sensor on the tokamak ISTTOK". • Severo JHF, Nascimento IC, Kuznetov Yu K, Tsypin VS, Elfimov AG, Galvão RMO, Alonso MP, Ruchko LF, Machida M, Ribeiro C, Usuriaga OC, Bellintani, V Jr Germano, TM, Sanada, EK Elizondo, JI Fagundes, AN, de Sá WP, and Tendler M, “Temporal evolution of plasma rotation measurement in tokamaks using an optical monochromator and two photomultipliers as detector”. • Valcárcel DF, IS Carvalho, BB Carvalho, H Fernandes, C Silva, P Duarte, A Duarte, PJ Carvalho e T Pereira, "Validation of ISTTOK Plasma Position Controller". ASDEX Upgrade Seminar, 22-25 October 2007, Kloster Seeon, Germany • Conway GD, C Tröster, S da Graça, ASDEX Upgrade & CFN Teams, “Pedestal fluctuations and GAMs”. 119 • Maraschek M, M Garcia Muñoz, S da Graça, S Günter, V Igochine, P Lauber, P Martin, P Piovesan, K Sassenberg, H Zohm, ASDEX Upgrade Team, “Experimentalists view on fast particle driven mode”. Arcus – 3 rd France-Russia Seminar, Metz, 7-9 November, 2007 • Heuraux S, E Gusakov, A Yu Popov, M Schubert, F da Silva, T Gerbaud, “The reflectometry as a multi-function diagnostic to characterize turbulence of fusion plasmas”. • Schubert M, S Heuraux, E Gusakov, A Popov, T Gerbaud, F da Silva, “On the absolute value of the density fluctuation measured by reflectometry”. 49 th Annual Meeting of the Division of Plasma Physics, Orlando - Florida, USA, 12-16 November 2007 • Budny RV, E Mazzucato, A Fonseca, R Bravenec, J Candy, RE Waltz, TFTR Team, EFDA-JET Collaboration, “Gyrokinetic simulations of electron density fluctuations and comparisons with measurement”. • Fonseca A, B Alper, R Budny, L Cupido, J Fessey, A Figueiredo, S Hacquin, ME Manso, E Mazzucato, L Meneses, A Sirinelli, M Walsh, and JET EFDA Contributors, "Radial correlation reflectometry measurements on the JET tokamak". 9 th Brazilian Meeting on Plasma Physics 25-28 November, São Pedro, SP, Brazil, 2007 • Berni LA, MP Alonso , JH Severo, FO Borges, JI Elizondo, M Machida, CAF Varandas, RMO Galvão, “Design of a Multipoint Thomson Scattering Diagnostic for the TCABR Tokamak”. • Berni LA, E del Bosco, MP Alonso, “10-Channel Thomson Scattering Diagnostic for the ETE Tokamak”. • Severo JHF, Bellintani V Jr, Kuznetov, Yu K, Nascimento IC, Tsypin VS, Guimarães-Filho Z O, Caldas IL, Elfimov A G, Galvão RMO, Alonso MP, Ruchko LF, Machida M, Ribeiro C, Usuriaga OC, Flores DAM, Germano TM, Sanada EK, Elizondo JI, Fagundes AN, and Sá de WP, “Spectroscopy study of the MHD activity”. 22.1.6. Other publications • Belo JH, and Dominique Guilhem, “Assessing the likelihood of arcing from brazing deficiencies in the C4 launcher by studying the electric fields inside its waveguides”, DRFCCEA report (2007) • Belo JH, and Dominique Guilhem, “Gauging how (small) changes in the position and depth of a single passive waveguide on the C4 LH launcher (could) affect the main parameters of its radiated spectrum”, DRFC-CEA report (April 2007) • Cupido L, M. Manso, “Proposal for a Profile Reflectometry System on JET”, internal report CFN/IST, August 2007. • Cupido L, M. Manso, L. Meneses, A. Silva, P. Varela, “Upgrade of the KG8a Sweeping Reflectometer to a Multi- Band System”, internal report CFN/IST, November 2007. • Cupido L, “Tecnologia de varrimento de HTOs com Sincronização de Fase/Frequência para aplicação em Reflectometria de Banda Larga”, internal report CFN/IST, August 2007. • Cupido L, “Status of technology for millimeter and submillimeter wave Reflectometry, ECE and ECA Diagnostics”, internal report CFN/IST, March 2007. • Cupido L, Reflectometria de Banda Larga em Tokamaks de grande Dimensão (ITER e JET) – limitações das tecnologias actuais, internal report CFN/IST, February 2007. • H&CD working group, LHCD Sub-group, contributors to the proposal, “A ‘day1’ LHCD system on ITER”, February 2007 • Santos J, M. Manso “Proposal for a real time electron density profile measurement diagnostic for ASDEX Upgrade”, internal report CFN/IST, June 2007. • Silva A, Zajac J, Manso M, “Design of reflectometry system for the Compass-D tokamak”, internal report CFN/IST, December 2007. • Varela P, M. Manso “Support to ITER Diagnostic Design, ITER Task: Plasma Position Reflectometry”, Contract: EFDA 03.1118, Final Report, Association EURATOM/IST, March 2007. 22.1.7. Projects/Funding awarded in 2007 • “Data Acquisition System for Compass-D”. • “Diagnostic Design for ITER - Plasma Position Reflectometer”, EFDA Contract Nº 06-1449. • “Microwave Diagnostics Engineering in preparation for ITER” EURATOM Fusion Training Scheme – EFDA Contract Nº 042961. • “JET Experimental Campaigns C18-C19”, JW7-O-IST- 30A. • “JET Gamma Ray Spectrometer”, JW7-OEP-IST-31. • “JET Plasma Control Upgrade”, JW5-TA-EP2-PCV-02. • “Integration of Transport and MHD Codes at JET”, EFDA- 30/4.6 • “Reequipment of the CFN Microwave Laboratory”, Fundação para a Ciência e Tecnologia. 22.1.8. Laboratorial prototypes • Mechanical plasma pressure sensor based on two pendulums whose heads are exposed to plasma, while the deflection is measured by high sensitivity semi-conductor strain gauges (Plasma Phys. Control. Fusion 49, 1783, 2007). 120 • Compact cantilever probe for plasma pressure measurements (Rev. Sci. Instrum. 034702, 2007). • Water cooled PC Cluster (Internal report 1/2007). • Eurocard Generic Microcontroller. • Multi-channel amplifier for the tomography diagnostic. • Bolometer tomography diagnostic based on 3 linear 10-pixel detectors (17 th IAEA TM on RUSFD, Oct. 2007). • High gain photodiode sensor for the ISTTOK spectrometer. • Full active bridge for the mechanical plasma pressure diagnostic. • A digital controlled high voltage (1.5kV) power supply for PMT’s. • Development of a real-time controller for the plasma position (17 th IAEA TM on RUSFD, Oct. 2007). • Fast rise-time digitally controlled power supplies for the ISTTOK plasma control system. • A five-channel retarding field energy analyzer for edge ion temperature measurements on TJ-II. • Bibet Ph., D Guilhem, JH Belo, et al, Prototype of the C4 PAM LH launcher module. • Bibet Ph., D Guilhem, JH Belo, et al, Prototype of the TE 10 - TE 30 mode converter for the PAM-C4 LH launcher. • Control and data acquisition Group, EPN-PCI, fast timing and event management board for the PCI bus. • Control and data acquisition Group, PMC-PCIe, 32-bit PMC interface card which provides one x1 PCIe fiber optical channel. • Control and data acquisition Group, ATCA-CONTROLLER- PCIe, ATCA double width blade compliant with the PCIe and ATX standards. • Control and data acquisition Group, ATCA-MIMO-ISOL, the card provides 32 analog input channels (digitizer/transient recorder) and 8 analog output channels (waveform generator). • Control and data acquisition Group, SR-TR-ATCA, ATCA board with eight acquisition channels per modul with dData transfer rate of up to 800 Mbyte/s over x4 PCI Express to the host processor. • Control and data acquisition Group, Test-Bench System of the JET RTP Phase 2 (JW3-TA-EP-RTP-01), the test-Bench system provides analogue and ATM stimulus signals to a real time control systems under test. • Control and data acquisition Group, Data Acquisition for the Gamma Ray diagnostics (JET-DNG), this system provides a modern data acquisition for the JET neutron camera. • Control and data acquisition Group, Real-time DSP-based control system for ISTTOK plasma position, this system acquires a set of 12 pick-up coils measuring the poloidal field from the plasma. 22.1.9. Numerical codes • Cross-spectrum analysis of the data from the Mirnov coils and determination of the poloidal/toroidal mode numbers. • Coherency analysis of cross diagnostic data (Mirnov, Heavy ion beam, X-ray Tomography) for fluctuation analysis in time/spatial content. • Kalman filtering approach to the real-time amplitude estimation of spectral harmonics involved in the magnetic field pitch angle determination using Motional Stark Effect diagnostic in JET. • Development of a SCAD – a cooperative software for shared tokamak operation. • Development of remote data access tools. • FusionTalk – Video Conference Web based tool. • FireCalc – Remote procedure invocation for job scripting submissions under general software (MatLab, IDL, SciLab Mathematica and others). • Tomographic reconstruction of the ISTTOK plasma emissivity. • Nave MFF, Sawtooth models in JETTO. • Nave MFF, ELM models in JETTO. • Ribeiro TT, Scott B, “SOL and self-consistent MHD equilibrium (including an X-point) in the 3-D gyrofluid turbulence model GEM”. • Goniche M, O. Izacard, D. Voyer, J.H.Belo, Codes SWAN and ALOHA for the coupling of LH. • Silva F, S. Heuraux, M. Manso, “Full wave 2D code using Finite Difference Techniques in the Time Domain (FDTD), with an unidirectional transparent source (UTS)”. 22.1.10. Organization of conferences and workshops • Nave MFF, (member of the Scientific Program Committee), 5 th International Conference on the Physics of Dusty Plasmas, Azores, Portugal, May 2008 • Silva C, chairman of the 17 th IAEA Technical Meeting on Research Using Small Fusion Devices, Lisbon, October 2007. 121 • Varandas C, chairman of the RUSFD, Lisbon, October 2007. • Varandas C and Serra F, members of the LOC of the 8 th IEA International Workshop on Beryllium Technology, ITN, Lisbon, December 2007. 22.1.11. Participation in scientific committees of conferences and workshops • Silva C, Workshop on Electric Fields, Turbulence and Self- Organisation in Magnetised Plasmas. 22.1.12. Ph.D thesis completed in 2007 • Silva, A, “The ASDEX Upgrade broadband microwave reflectometry system”, Universidade Técnica de Lisboa • Silva, F, “Finite-difference time-domain simulation of reflectometry in fusion plasmas”, Universidade Técnica de Lisboa 22.1.13. Other activities • Bizarro JP, Co-author of the LITE (Lower-Hybrid and Ion- Cyclotron Technology) proposal on RF enginnering within the EFDA Goal Oriented Training Programme, a collaboration among the Associatons Euratom-IST, Euratom-CEA, Euratom-ENEA, Euratom-IPP and Euratom-Belgian State. • Cupido L, Consultant of the United States – DOE (Department of Energy) for the evaluation of scientific proposals for public (US) funding. • Manso M, Coordination of the project on “Microwave Diagnostics Engineering in preparation for ITER” of the EURATOM Fusion Training Scheme • Manso M, Jury member (rapporteur) – Thèse d´habilitation à diriger des recherches de Dr. Fréderic Clairet, March 2007, Université de Marseille, France. • Ribeiro TT, Participation in the “EFDA Task Force on Integrated Tokamak Modelling” within the turbulence project (IMP4), and in the European DEISA project in collaboration with the Max-Planck-Gesellschaft Computer Centre (RZG). • Silva F, Invited expert at the 1st European Reflectometry Simulation Code Meeting, Garching, Germany, 29–30 October 2007. • Varandas CAF and EFDA Public Information Group, “Interview to Carlos Varandas”, Fusion News Newsletter, Vol. 1, 8, March 2007. • Organization of the ISTTOK Joint Experiment in collaboration with the IAEA with the participation of 24 scientists from 13 countries. 22.1.14. Collaborations • Associación Euratom/CIEMAT, Madrid (Estrada T, Hidalgo C). • Association EURATOM/HAS, Hungary. • Association EURATOM/ENEA, CNR – Milan, Italy (Lazzaro, E, Simonetto). • CRPP, Lausanne (Duval B, Moret JM) • CSU EFDA JET, United Kingdom (Morlock C). • Departamento Engenharia Electrotécnica Computadores, IST, Portugal (Silva FM and Nunes F) • DRFC/CEA Cadarache, France (Clairet F, Goniche M, Guilhem G, Litaudon X, Sabot R). • ERM/KMS, Belgium (Ongena J). • EURATOM/University of Latvia, Institute of Solid State Physics, Riga, Latvia. • Humboldt-Universitat zu Berlin, Germany. • IEPPG, Institute for Ion Physics and Applied Experimental Physics, Association EURATOM/ÖAW, University of Innsbruck, Innsbruck, Austria. • INETI, Departamento de Materiais e Tecnologias de Produção, Estrada do Paço do Lumiar, Lisboa, Portugal. • Institut Ioffe, Saint Petersbourg, Russian Federation (Gusakov E). • Institute of Plasma Physics, IPP.CR, Prague, Czech Republic (Zajac J, Pavlo P). • Instituto de Telecomunicações, IST (Fernandes C). • Laboratório de Física de Plasmas, Universidade de São Paulo, Brasil (Elfimov A, Galvão R). • Laboratoire de Physique des Millieux Ionisés et Applications da Université Henri Poincaré, Nancy, França (Heuraux S). • Max Planck Institut fuer Plasma Physik, Greifswald, Germany (Hirsh M). • Max-Planck Institut fuer Plasmasphysik, Garching, Germany (Behler K, Conway G, Coster D, Lang P, Maraschek M, Scott B, Zohm H). • UKAEA Culham, United Kingdom (Parail V, Sharapov S, Walsh M). • Université des Marseille, France (Briolle F, Gendrih P). • VTT, Finland (Tala T). 22.2. TECHNOLOGIES OF PLASMAS AND LASERS 22.2.1. Publications in refereed scientific journals (publications in ISI) • Ali S, Moslem WM, Shukla PK and Kourakis I, “Fully nonlinear ion-sound waves in a dense Fermi magnetoplasma”, Physics Letters A, 366 (6): 606-610 Jul 9 2007. • Ali S and Shukla PK, “Streaming instability in quantum dusty plasmas”, European Physical Journal D, 41 (2): 319- 324 Feb 2007. • Álvarez R and Alves LL, “Two-dimensional electromagnetic model of a microwave plasma reactor operated by an axial injection torch”, Journal Applied Physics 101: 103303 1–6 May 2007. • Alves LL, “Fluid modelling of the positive column of directcurrent glow discharges”, Plasma Sources Science and Technology 16: 557–569 June 2007 Paper originally presented at the European Summer School ‘Low Temperature Plasma Physics: Basics and Applications’ and ‘Master Class: Biotechnical and Medical Applications’ (Bad Honnef, Germany, 26 September–8 October 2004). • Bertolami O, Boehmer, CG Harko T and Lobo FSN, “Extra force in f(R) modified theories of gravity”, Physical Review D75: 104016 2007 122 • Bertolami O and Carvalho C, “Spontaneous symmetry breaking in the bulk as a localization mechanism of fields on the brane”, Physical Review D76: 104048 2007 • Bertolami O and Paramos J, “A Mission to test the Pioneer anomaly: Estimating the main systematic effects”, International Journal Modern Physics D16: 1611-1623 2007 • Bertolami O, Pedro, FG and Delliou ML, “Dark Energy-Dark Matter Interaction and the Violation of the Equivalence Principle from the Abell Cluster”, Physics Letters B654: 165- 169 2007 • Bhowmika C, Misrab AP and Shukla PK, “Oblique modulation of electron-acoustic waves in a Fermi electron-ion plasma”, Physics of Plasmas, 14 (12): Art. No. 122107 Dec 2007 • Bingham R, Silva LO, Mendonca JT, Shukla PK, Mori WB and Serbeto A, “Plasma wakes driven by neutrinos, photons and electron beams”, International Journal of Modern Physics B 21 (3-4): 343-350 Feb 2007 • Dias FM and Popov Tsv, “EEDF probe measurements: differentiation methods, noise, and error”, J. Physics: Conference Series 63: 012005 (16pp) 2007 • Diaz AM, Garcia OE, Diaz JP, Exposito FJ, Utrillas MP, Martinez-Lozano JA, Alados-Arboledas L, Olmo FJ, Lorente J, Cachorro V, Horvath H, Labajo A, Sorribas M, Vilaplana JM, Silva AM, Elias T, Pujadas M, Rodrigues JA and Gonzalez JA, “Aerosol radiative forcing efficiency in the UV region over southeastern Mediterranean: VELETA2002 campaign”, Journal of Geophysical Research-Atmospheres, 112 (D6): Art. No. D06213 Mar 31 2007 • Eloy M, Guerreiro A, Mendonça JT and Bingham, R, “Hamiltonian formulation of direct laser acceleration in vacuum”, Journal of Plasma Physics, 73: 635-647 Part 5 Oct 2007 • Figueira G, Wemans J, Pires H, Lopes NC and Cardoso L, “Single adjuster deformable mirror with four contact points for simultaneous correction of astigmatism and defocus”, Optics Express 15: 5664-5673 2007 • Gargaté L, Bingham R, Fonseca RA, and Silva LO, “dHybrid: A massively parallel code for hybrid simulations of space plasmas”, Computer Physics Communications 176 (6): 419- 425 Mar 15 2007 • Guerra V, “Analytical model of heterogeneous atomic recombination on silicalike surfaces”, IEEE Transactions on Plasma Science 35: 1397–1412 2007 • Guerra V, Sá PA and Loureiro J, “Nitrogen pink afterglow: the mystery continues”, Journal of Physics Conference Series 63: 012007 2007 • Guerra V and de Abreu R, Comment on: “From classical to modern ether-drift experiments: the narrow window for a preferred frame” [Phys. Lett. A 333 (2004) 355], Physics Letters A 361: 509–512 2007 • Guerreiro A, Eloy M, Mendonca JT and Bingham R, “Dipolar radiation from spinning dust grains coupled to an electromagnetic wave”, Journal of Plasma Physics, 73: 555- 563 Part 4 Aug 2007 • Krasheninnikov SI, Shevchenko VI and Shukla PK, “Spinning of a charged dust particle in a magnetized plasma”, Physics Letters A, 361 (1-2): 133-135 Jan 22, 2007 • Kutasi K, Pintassilgo CD, Loureiro J and Coelho PJ, “Active species in a large volume N 2 -O 2 post-discharge reactor”, Journal of Physics D: Applied Physics 40: 1990–2001 2007 • Kutasi K and Loureiro J, “Role of the wall reactor material on the species density distributions in an N 2 -O 2 postdischarge for plasma sterilization”, Journal of Physics D: Applied Physics 40: 5612–5623 2007 • Lancaster KL, Green JS, Hey DS, Akli KU, Davies JR, Clarke RJ, Freeman RR, Habara H, Key MH, Kodama R, Krushelnick K, Murphy CD, Nakatsutsumi M, Simpson P, Stephens R, Stoeckl C, Yabuuchi T, Zepf M and Norreys PA, “Measurements of Energy Transport Patterns in Solid Density Laser Plasma Interactions at Intensities of 5 x 10 20 W cm -2 ”, Physical Review Letters 98 (12): Art. No. 125002 Mar 23 2007 • Lino da Silva M, Guerra V and Loureiro J, “State-resolved dissociation rates for extremely nonequilibrium atmospheric entries”, Journal of Thermophysics and Heat Transfer 21(1): 40–49 2007 • Lino da Silva M, Guerra V and Loureiro J, Nonequilibrium dissociation processes in hyperbolic atmospheric entries, Journal of Thermophysics and Heat Transfer 21(2): 303–310 2007 • Lino da Silva M, Guerra V and Loureiro J, “Twotemperature models for nitrogen dissociation”, Chemical Physics 342: 275–287 2007 • Lino da Silva M, “An adaptive line-by-line-statistical model for fast and accurate spectral simulations in low-pressure plasmas”, Journal of Quantitative Spectroscopy and radiative Transfer, 108(1): 106–125 2007 • Lu W, Tzoufras M, Tsung FS, Joshi C, Mori WB, Vieira J, Fonseca RA and Silva LO, “Generating Multi GeV electron bunches using single stage laser wake field acceleration in a 3D nonlinear blowout regime”, Physical Review Special Topics-Accelerators and Beams 10 (6): Art. No. 061301 Jun 2007 • Marques LSA, Jolly J and Alves LL, “Electrical characterization of capacitively-coupled radio-frequency discharges in hydrogen”, Plasma Process & Polymers 4: S937–S941 2007 • Marques L, Fernandes AC, Vaz F and Ramos MMD, “Influence of oxygen addition on the structural and elastic properties of TiC thin films”, Plasma Process & Polymers 4: S195 2007 123 • Marques L, Jolly J and Alves LL, “Capacitively coupled radio-frequency hydrogen discharges: The role of kinetics”, Journal Applied Physics 102: 063305 1–14 Sep 2007 • Martins AA and Pinheiro MJ, “The connection between inertial forces and the vector potential”, American Institute of Physics Conference Proceedings 880: 1189–1200 (2007) • Mendonca, JT, “Axion excitation by intense laser fields”, European Physica Letters, 79 (2): Art. No. 21001 2007 • Mendonca JT and Shukla PK, “Excitation of ion-acoustic perturbations by incoherent kinetic Alfven waves in plasmas”, Physics of Plasmas, 14 (12): Art. No. 122304 Dec 2007 • Mendonca JT, Silva LO and Bingham R, “Reflection of an electron beam by a photon mirror”, Journal of Plasma Physics 73: 627-634 Part 5 Oct 2007 • Moslem WM, Kourakis I, Shukla PK and Schlickeiser R, “Nonlinear excitations in electron-positron-ion plasmas in accretion disks of active galactic nuclei”, Physics of Plasmas, 14 (10): Art. No. 102901 Oct 2007 • Moslem WM, Kourakis I and Shukla PK, “Finite amplitude envelope solitons in a pair-ion plasma”, Physics of Plasmas, 14 (10): Art. No. 109902 Oct 2007 • Moslem WM, Shukla PK, Ali S and Schlickeiser R, “Quantum dust-acoustic double layers”, Physics of Plasmas, 14 (4): Art. No. 042107 Apr 2007 • Peano F, Coppa G, Peinetti F, Mulas R and Silva LO, “Ergodic model for the expansion of spherical nanoplasmas”, Physical Review E 75 (6): Art. No. 066403 Part 2 Jun 2007 • Peano F, Martins JL, Fonseca Ra, Silva LO, Coppa G, Peinetti F and Mulas R, “Dynamics and control of the expansion of finite-size plasmas produced in ultraintense laser-matter interactions”, Physics of Plasmas 14 (5): Art. No. 056704 May 2007 • Pinheiro MJ, “Anomalous Diffusion at Edge and Core of a Magnetized Cold Plasma”, Journal of Physics D: Conference Series 71: 102002–012014 2007 • Pinheiro MJ, “Do Maxwell's equations need revision? - A methodological note”, Physics Essays 20(2) 2007 [Los Alamos ArXives:physics/0511103] • Pinheiro MJ, “Electron trapping by electric field reversal in Glow Discharges, in Gas Discharges -Fundamentals and Applications” (J de Amorim Filho ed.), Research SignPost, Trivandrum, India 2007 • Pintassilgo CD, Kutasi K and Loureiro J, “Modelling of a lowpressure N 2 -O 2 discharge and post-discharge reactor for plasma sterilization”, Plasma Sources Science and Technology 16: S115–S122 2007 • Pintassilgo CD, Jaoul C, Loureiro J, Belmonte T and Czerwiec T, “Kinetic modelling of a N 2 flowing microwave discharge with CH 4 addition in the post-discharge for nitrocarburising treatments”, Journal of Physics D: Applied Physics 40: 3620–3632 2007 • Resendes DP, Mota S, Mendonca JT, Sanders B, Encarnacao J and del Amo JG, “Laser propulsion for ground launch”, Journal of Propulsion and Power 23 (1): 73-80 Jan-Feb 2007 • Ricard A, Henriques J, Cousty S, Villerger S and Amorin J, “Determination of N, H and O–atom in N 2 –H 2 and in N 2 –H 2 gas mixtures by optical actinometry in flowing microwave discharges and NO titration in post–discharges”, Plasma Process & Polymers 4: S965–S968 2007 • Rus B, Mocek T, Kozlova M, Polan J, Homer P, Stupka M, Tallents GJ, Edwards MH, Mistry P, Whittaker DS, Booth N, Zhai Z, Pert GJ, Dunn J, Nelson AJ, Foord ME, Shepherd R, Rozmus W, Baldis HA, Fajardo M, De Lazzari D, Zeitoun P, Jamelot G, Klisnick A, Ros D, Cassou K, Kazamias S, Bercego H, Danson C, Hawkes S, Juha L, Hajkova V, Chalupsky J, Feldhaus J, Wabnitz H, Nejdl J, Kuba J, Davidkova M and Stisova V, “Development and applications of multimillijoule soft X-ray lasers”, Journal of Modern Optics, 54:16, 2571 - 2583 (2007) • Santos JE, Silva LO and Bingham R, “White-light parametric instabilities in plasmas”, Physical Review Letters 98 (23): Art. No. 235001 Jun 8 2007 • Shukla PK, “Generation and dynamics of plasma blobs in partially ionized tokamak scrape-off-layer”, Physics Letters A, 371 (5-6): 453-456 Nov 26 2007 • Shukla PK, “Purely growing electromagnetic mode driven by ion-temperature anisotropy in a collisional plasma”, Physics Letters A, 370 (3-4): 316-318 Oct 22 2007 • Shukla PK, “Extraordinary electromagnetic waves in a warm dense magnetoplasma”, Physics Letters A, 369 (4): 312-314 Sep 24 2007 • Shukla PK, Coppi B and Eliasson B, “Electron parallel velocity and temperature gradient driven electrostatic fluctuations in nonuniform magnetoplasmas”, Physics of Plasmas, 14 (1): Art. No. 014504 Jan 2007 • Shukla N, Moslem WM and Shukla, PK, “Instability of electromagnetic waves in a self-gravitating rotating magnetized dusty plasma with opposite polarity grains”, Physics of Plasmas, 14 (5): Art. No. 053702 May 2007 • Shukla N and Shukla PK, “Generation of magnetic field fluctuations in relativistic electron-positron magnetoplasmas”, Physics Letters A 362 (2-3): 221-224 Feb 26 2007 • Shukla N and Shukla PK, “A new purely growing instability in a strongly magnetized nonuniform pair plasma”, Physics Letters A, 367 (1-2): 120-122 Jul 16 2007 • Shukla N, Shukla PK, Liu CS and Morfill GE, “Generation of magnetic fields in a positive-negative dusty plasma”, Journal of Plasma Physics, 73: 141-144 Part 2 Apr 2007 124 • Shukla N, Shukla PK and Morfill GE, “Amplification of magnetic fields by polaritonic flows in quantum pair plasmas”, Journal of Plasma Physics, 73: 289-293 Part 3 Jun 2007 • Shukla PK, Shukla N and Stenflo L, “Enhanced electromagnetic emission from plasmas containing positive dust grains and electrons”, Physics Letters A, 365 (1-2): 131- 134 May 21 2007 • Shukla PK, Shukla N and Stenflo L, “Kinetic modulational instability of broadband dispersive Alfven waves in plasmas”, Journal of Plasma Physics, 73: 153-157 Part 2 Apr 2007 • Shukla PK and Stenflo L, “Nonlinear interactions between upper-hybrid and Alfven modes in a magnetized plasma containing charged dust impurities”, Journal of Plasma Physics, 73: 3-8 Part 1 Feb 2007 • Siebold M, Hornung M, Bock S, Hein J, Kaluza MC, Wemans J and Uecker R, “Broad-band regenerative laser amplification in ytterbium-doped calcium fluoride (Yb:CaF 2 )”, Applied Physics B 84: 543-547 2007 • Tatarova E, Dias FM, Ferreira CM and Puac N, “Spectroscopic Determination of H, He and H2 Temperatures Profiles in a Large-Scale Microwave Plasma Source”, Journal Applied Physics 101: 063306 2007 • Tatarova E, Dias FM, Puac N and Ferreira CM, “Hydrogen Balmer Line Broadening in a Microwave Plasma Source”, Plasma Sources Science and Technology 16: S52–S56 2007 • Tatarova E, Guerra V, Henriques J and Ferreira CM, “Nitrogen Dissociation in Low-Pressure Microwave Plasmas”, J. Physics: Conference Series 71: 012010 2007 • Tatarova E, Dias FM, Felizardo E, Henriques J, Ferreira CM and Gordiets B, “Microwave plasma torches driven by surface waves”, Plasma Sources Science and Technology (printed version on the net) 2008 • Trines R, Bingham R, Dunlop MW, Vaivads A, Davies JA, Mendonca JT, Silva LO and Shukla PK, “Spontaneous generation of self-organized solitary wave structures at earth's magnetopause”, Physical Review Letters 99 (20): Art. No. 205006 Nov 16 2007 • Tzoufras M, Ren C, Tsung FS, Tonge JW, Mori WB, Fiore M, Fonseca RA, and Silva LO, “Stability of arbitrary electron velocity distribution functions to electromagnetic modes”, Physics of Plasmas 14 (6): Art. No. 062108 Jun 2007 • Vieira J, Fonseca RA, Silva LO, Lu W, Tzoufras M, Tsung FS and Mori WB, “Sheet crossing and wave breaking in the laser wakefield accelerator”, International Journal of Modern Physics B 21 (3-4): 439-446 Feb 2007 22.2.2. Invited Talks in Conferences • Bertolami O, “Searching for the nature of dark energy and dark matter”, VI Workshop Nova Física no Espaço, Campos do Jordão, São Paulo, Brazil, February 2007 • Bertolami O, “The Pioneer Explorer Collaboration: Second Team Meeting at ISSI”, International Space Science Institute, Bern, Switzerland, February 2007 • Bertolami O, “From Quantum to Cosmos”, Space-based research in fundamental physics and quantum technologies, Bremen, Germany, June 2007 • Bertolami O, Encuentros Relativistas Españoles - Spanish Relativity Meeting, Puerto de La Cruz, Tenerife, Spain, September 2007 • Bertolami O, Scientific and Fundamental Aspects of the Galileo Programme, Cité de l’Espace, Toulouse, France, October 2007 • Davies JR, “The Effect of Magnetic Field on Electron Beam Propagation in Plasmas”, 5 th Direct Drive and Fast Ignition Workshop, Madrid, Spain, April 2007 • Davies JR, Fajardo M and Rus B, “Magnetic Field Driven Filamentation in Laser Ablation of Solids”, Theory of Short Pulse Petawatt Laser Plasma Interaction - Laserlab Europe Workshop, Darmstadt, Germany, October 2007 • Guerra V, “Vibration-to-Electronic energy transfers in the nitrogen afterglow”, Workshop on Streamers, sprites, leaders, lightning: from micro- to macroscales, Leiden, The Netherlands, October 2007 • Guerra V, “Special Relativity as a simple geometry problem”, Sixth Int. Workshop on Applied Category Theory, Graph-operad-logic, Special Relativity, Dynamics and Electromagnetics, Ixtapa, Mexico, February 2007 • Lopes NC, Bendoyro RA, Berardo J, Dias JM, Figueira G, Fiúza F, Fonseca RA, Lemos N, Marti M, Martins J, Martins SF, Onofrei RI, Peano F, Vieira JM and Silva LO, “Research on laser-plasma accelerators at GoLP-IST- Lisbon”, Laser and plasma accelerators workshop 2007, Angra do Heroismo, Ilha Terceira, Açores, Portugal, July 2007 • Páramos J, Scientific and Fundamental Aspects of the Galileo Programme, Cité de l’Espace, Toulouse, France, October 2007 • Peano F, Vieira J, Fonseca RA, Silva LO and Bingham R, “Direct acceleration of muons with variable-frequency lasers”, Topical workshop on The Neutrino Factory and Muon Collider, the physics and the R&D programmes, The Cosener's House, Abingdon, Oxfordshire, UK, October 2007 • Silva LO, “Control of the explosions of nanoplasmas”, Dream Beams Symposium, Max Planck Institute for Quantum Optics, Munich, Germany, February 2007 • Silva LO, “White light parametric instabilities in plasmas” and “Expansions/explosions of nanoplasmas”, Invited Lecturer at the Summer College on Plasma Physics, International Center for Theoretical Physics, Trieste, Italy, August 2007 125 • Tatarova E, “Microwave discharges in molecular gases driven by surface waves”, 28 th ICPIG (International Conference on Phenomena in Ionized Gases), Prague, Czech Republic, July 2007, Book of Abstracts, p.179 • Tatarova E, “Hydrogen Balmer Lines Broadening in Microwave Plasma Sources”, 60 th GEC (Annual Gaseous Electronics Conference), Arlington, Virginia, USA, October 2007 • Vieira J, Peano F, Fonseca RA, Fiuza F, Martins JL, Silva LO, Huang C, Tsung F and Mori WB, “One-to-one kinetic simulations of intense laser-matter interactions”, Laserlab Europe Workshop, Darmstadt, Germany, October 2007 22.2.3. Oral Contributions Alpha-X Workshop, Lisbon, Portugal, October 2007 • Fiúza F, Martins SF, Fonseca RA and Silva LO, “Novel effects in ionization fronts” • Gallacher JG, Jaroszynski DA, Lemos N, Dias JM, Sun J, and Issac RC, “Relativistic Plasma Mirrors” • Lemos N, Dias JM, Onofrei RI, Lopes NC, Figueira G, Fiuza F, Silva LO, Gallacher JG, Issac RC and Jaroszynski DA, “Formation of Plasma Channels by ultra-short laser pulses in gas jets” • Lopes NC and Fajardo M, “Path to laser-plasma based seeded FEL” • Vieira J, Fiuza F, Fonseca RA, Martins SF, Silva LO, Huang C, Tsung FS and Mori WB, “One-to-one full scale kinetic modeling of the LWFA” 60 th Annual Gaseous Electronics Conference, Arlington, Virginia, USA, October 2007 • Guerra V, Lino da Silva M, Gocić S and Loureiro J, “An improved description of the vibrational energy transfers in nitrogen discharges”, Bulletin American Physical Society 52: 12 Oct 2007 • Henriques J, Tatarova E, Felizardo E, Dias FM and Ferreira CM, “Microwave Plasma Torches Driven by Surface Waves”, Bulletin American Physical Society 52: 15 Oct 2007 49 th APS Annual Meeting of the Division of Plasma Physics, Orlando, Florida, USA, November 2007 • Silva LO, “White light parametric instabilities” Conference on Lasers and Electro-Optics (CLEO-EUROPE), Munich, Germany, June 2007 • Cardoso L, Figueira G, Pires H and Wemans J, “Experimental results on ultra-broadband OPCPA” • Wemans J, Siebold M, Figueira G, Lopes N, Cardoso L, Hein J and Diaz F, “Ytterbium-based regenerative amplification at 1053 nm” CLF High Power Laser Science Christmas Meeting, Abingdon, December 2007 • Valente J, Onofrei R, Fiuza F, Davies JR, Ma T and Beg FN “XUV imaging as a diagnostic for fast electron transport: statistical analysis” 34 th EPS Conference on Plasma Physics, Warsaw, Poland, July 2007 • Fiore M, Marti M, Fonseca RA and Silva LO, “Enhancement of the filamentation instability due to collisions” • Peano F, Silva LO and Coppa G, “Dimensional collapse in Coulomb explosions” Frontiers in Low Temperature Plasma Diagnostics VII, Beverly, UK, April 2007 • Dias FM, “Combined multi-harmonic - numerical, adaptive differentiation: analysis of the noise level influence on speed improvement” Laser and Plasma Accelerators Workshop 2007, Azores, Portugal, July 2007 • Gallacher JG, Lemos N, Sun J, Dias JM, Issac RC, Fonseca RA, Silva LO, Lopes NC, Mendonça JT and Jaroszynski DA, “Optical pulse tailoring using THz pulses” • Najmudin Z, Bellei C, Bingham R, Bourgeois N, Brunetti E, Clarke RJ, Collier J, Dangor AE, Divall EJ, Fiúza F, Fonseca RA, Foster PS, Gallagher J, Gonsalves AJ, Gopal A, Hooker CJ, Hooker SM, Heathcote R, Jaroszynski DA, Kaluza MC, Kamperidis C, Kneip S, Karsch S, Krushelnick K, Lancaster KL, Langley AJ, Lopes N, Mangles S, Marsh K, Marquès JR, Maksimshuk A, Mendonça JT, Murphy C, Mori WB, Nazarov W, Nagel SR, Nilson P, Norreys PA, Ta Phuoc K, Reed SA, Reitsma A, Rowlands-Rees TP, Schreiber J, Silva LO, Thomas A, Trines R, Vieira J, Viskup R and Willingale L, “Plasma based particle acceleration experiments at Imperial College” • Peano F, Vieira J, Fonseca RA and Silva LO, “Numerical analysis of the electron injection with colliding pulses in laser-wakefield accelerators” • Peano F, Vieira J, Fonseca RA, Silva LO, Coppa G and Mulas R, “Direct acceleration of ions with counterpropagating lasers” • Vieira J, Fiúza F and Silva LO, “Self-Steepening of intense laser pulses in plasmas” • Vieira J, Fonseca RA, Silva LO, Huang C, Lu W, Tzoufras M, Tsung F, Mori WB, Cooley J and Antonsen T, “Simulations of Laser Wake Field Acceleration in channels using QuickPIC” Space Technology International Forum, Albuquerque, NM, USA, February 2007 • Martins AA and Pinheiro MJ, “The connection between Inertial Forces and the Vector Potential” 126 22.2.4. Poster Contributions Advanced Solid-State Photonics, Vancouver, Canada, January 2007 • Siebold M, Jochmann A, Hornung M, Bock S, Hein J, Kaluza MC, Podleska S, Boedefeld R, Uecker R, Wehrhan O, Roeser F and Wemans J, “Characterization of Ytterbium-doped CaF2 for broadband regenerative pulse amplification” American Geophysical Union Fall Meeting, San Francisco, California, USA, December 2007 • Gargaté L, Bingham R, Fonseca RA, Bamford R and Silva LO, “Hybrid simulations of energetic ion interaction with mini magnetospheres” • Bamford R, Bingham R, Gibson KA, Thornton A, Bradford J, Hapgood M, Gargate L, Silva LO, Norberg C, Todd T, Wilson H and Stamper R, “Initial experimental results of a laboratory mini-magnetosphere for astronaut protection” 38 th AIAA Plasmadynamics and Lasers Conference in conjunction with the 16 th International Conference on MHD Energy Conversion, Miami, Florida, USA xxx 2007 • Bauville G, Lacour B, Magne L, Puech V, Santos Sousa J, Bœuf JP, Hagelaar G, Munoz-Serrano E, Pitchford LC, Sadeghi N and Touzeau N, “Experimental and Theoretical Study of Singlet Delta Oxygen Production in Microcathode Sustained Discharges”, AIAA Paper 2007-4025 49 th APS Annual Meeting of the Division of Plasma Physics, Orlando, Florida, USA, November 2007 • Fiúza F, Fonseca RA and Silva LO, “Phase-matched evenharmonics generation in relativistic ionization fronts” • Fonseca RA, Gargaté L, Martins SF, Peano F, Vieira J, Silva LO and Mori WB, “Detailed numerical modeling of electron injection in the Laser Wakefield Accelerator: Particle Tracking Diagnostics in PIC codes” • Gargaté L, Bamford R, Bingham R, Fonseca RA and Silva LO, “Hybrid Simulations of Mini Magnetospheres in the Laboratory” • Lu W, Tzoufras M, Huang C, Tsung FS, Mori WB, Vieira J, Fonseca RA Silva LO, Cooley J and Antonsen Jr T, “Design and Simulation of a single 100 GeV stage in LWFA” • Martins SF, Fonseca RA, Mori WB and Silva LO, “Numerical study of ultra-relativistic electromagnetic filamentation in boosted frames” • Martins JL, Peano F, Gargaté L, Fonseca R and Silva LO, “Interaction of intense lasers with nanostructured plasmas” • Peano F, Vieira J, Fonseca RA, Silva LO, Coppa G and Mulas R, “Direct ion acceleration with variable-frequency lasers” • Silva LO, Bingham R, Brandao B and Santos JP, “Transverse modulation instability of white light in plasmas” • Trines R, Murphy C, Bingham R, Lancaster K, Chekhlov O, Norreys P, Mendonca JT, Silva L, Mangles S, Kamperidis C, Thomas A, Krushelnick K and Najmudin Z, “Photon acceleration and modulational instability during wakefield excitation using long laser pulses” • Tzoufras M, Lu W, Huang C, Tsung FS, Mori WB, Vieira J, Fonseca RA and Silva LO, “Beam loading of the blowoutregime of laser/plasma wakefield acceleration” • Vieira J, Fiúza F and Silva LO, “Self-steepening of intense laser pulses in plasmas” 60 th Annual Gaseous Electronics Conference, Arlington, Virginia, USA, October 2007 • Álvarez R, Marques L and Alves LL, “2D Electromagnetic and hydrodynamic models of a microwave plasma torch”, Bulletin American Physical Society 52: 27 Oct 2007 • Gregório J, Synek P, Alves LL, Boisse-Laporte C, Leprince P, Leroy O and Teulé-Gay L, “Study of a 2.45 GHz microwave micro-plasma in air”, Bulletin American Physical Society 52: 22 Oct 2007 • Guerra V, “Study of the influence of collisions between physisorbed atoms on the surface recombination probability”, Bulletin American Physical Society 52: 46 Oct 2007 • Isola L, Gómez BJ, Feugeas JN and Guerra V, “Dependence of the emission intensities with the flow in pulsed N 2 dc discharges”, Bulletin American Physical Society 52: 38 Oct 2007 • Pinhão N, Pinheiro MJ and Donko Z, “Effect of H2 and N2 impurities in Argon on the kinetics of electrons”, Bulletin American Physical Society 52: Oct 2007 • Pitchford LC, Makasheva K, Callegari Th, Boeuf JP, Santos Sousa J and Puech V, “Study of the transition between MicroHollow Cathode Discharge and MicroCathode Sustained Discharge in a 3-electrode system”, Bulletin American Physical Society 52: Oct 2007 • Tatarova E, Dias FM, Gordiets B and Ferreira CM, “Hydrogen Balmer-Line Broadening in a Water Vapor Microwave Plasma Source”, Bulletin American Physical Society 52: 38 Oct 2007 AstroGPU 2007 — Workshop on General Purpose Computation on Graphics Processing Units in Astronomy and Astrophysics, IAS, Princeton, USA, November 2007 • Abreu P, Pereira JM and Silva LO, “A distributed memory GPU implementation of the Boris particle pusher algorithm” CLF High Power Laser Science Christmas Meeting, Abingdon, December 2007 • Davies JR, Fiuza F, Silva L, Honrubia JJ, Norreys PA, Robinson APL and Sherlock M, “Integrated Numerical Modelling for the Design of Laser - Plasma Experiments” E-MRS Spring Meeting, Strasbourg, France 2007 • Marques L and Carvalho S, “Ab initio study of structural and elastic properties of (Ti,Si,Al)N thin films” 127 2 nd European Planetary Science Congress, Postdam, Germany August 2007 • Pintassilgo CD and Loureiro J, “Numerical study of Titan's atmosphere using a N 2 -CH 4 post-discharge” 34 th EPS Conference on Plasma Physics, Warsaw, Poland, July 2007 • Dias FM and Popov Tsv K, “Data Processing of Electrical Probe Data Measured in TOKAMAKs”, ECA 31F, P-5.080 • Fiúza F, Fonseca RA and Silva LO, “Generation of relativistic even-harmonics in uniform underdense plasmas”; proceeding paper at http://www.eps2007.ifpilm.waw.pl/pdf/P4_013.pdf. • Gargaté L, Bingham R, Fonseca RA and Silva LO, “Massively parallel simulations of coronal mass ejections” • Marti M, Peano F, Fiore M, Fonseca RA and Silva LO, “Collisional algorithm for relativistic PIC codes” • Martins JL, Peano F, Fonseca R and Silva LO, “Relativistic harmonic generation in clusters” proceeding paper at http://epsppd.epfl.ch/Warsaw/pdf/P4_014.pdf. • Peano F, Silva LO and Coppa G, “Dimensional collapse in Coulomb explosions” • Popov Tsv K, Ivanova P, Stöckel J, Dejarnac R and Dias FM, “EEDF Measurements in the CASTOR Tokamak Using the First Derivative Langmuir Probe Method”, ECA 31F, P-5.104 • Shukla N, Shukla P, Fonseca RA, Sorasio G and Silva LO, “Generation of magnetic field fluctuations in relativistic electron–positron magnetoplasmas” • Silva LO, Santos JP and Bingham R, “Filamentation of intense broadband radiation in plasmas” • Sorasio G, Fonseca RA and Silva LO, “Laser-plasma interaction with thin targets proton acceleration above 300 MeV” • Tonge J, Tzoufras M, Tsung FS, Mori WB, Ren C, Marti M and Silva LO, “Fast ignition with ultra-high intensity lasers” • Vieira J, Fonseca RA, Silva LO, Lu W, Tzoufras M, Tsung FS and Mori WB, “Self guided propagation of intense laser pulses in the blowout regime” 4 th European Space Weather Week, Brussels, Belgium, November 2007 • Bamford R, Bingham R, Thornton A, Gibson KA, Gargate L, Bradford J, Fonseca RA, Silva LO, Mendonça JT, Hapgood M, Norberg C, Todd T, Wilson H and Stamper R, “Raise shields, Scotty: initial experimental results of a laboratory mini-magnetosphere for astronaut protection” 12 th European Summer School on Low Temperature Plasma Physics: Basics and Applications, Bad Honnef, Germany, October 2007 • Gregório J, Synek P, Alves LL, Boisse-Laporte C, Leprince P, Leroy O and Teulé-Gay L, “Study of a 2.45 GHz microwave micro-plasma in air” • Pitchford LC, Makasheva K, Callegari Th, Boeuf JP, Santos Sousa J and Puech V, “Study of the transition between MicroHollow Cathode Discharge and MicroCathode Sustained Discharge in a 3-electrode system” Hasylab Users Meeting, January 2007 • Timneanu N, Abreu E et al., “Coulomb induced acceleration of protons with FLASH and prospects of nuclear fusion” Ibergrid — 1 st Iberian Grid Infrastructure Conference, Santiago de Compostela, Spain, May 2007 • Abreu P, Pereira JM and Silva LO, “Exposing stream processors as Grid services: a GPGPU example” 16 th International Colloquium on Plasma Processes, Toulouse, France, June 2007 • Álvarez R and Alves LL, “Electromagnetic characterization of a microwave-driven mini-plasma reactor operated by an axial injection torch”, p.112 (Société Française du Vide ed.) • Lallement L, Cardinaud C, Rhallabi A and Alves LL, “Electrical properties and transport phenomena in Inductive Coupled Plasma discharges: experimental and simulation approaches”, p.124 (Société Française du Vide ed.) 20 th International Conference on the Numerical Simulation of Plasmas, Austin, Texas, USA, October 2007 • Fonseca RA, Marti M, Martins SF, Silva LO, Tonge J, Tsung F and Mori WB, “OSIRIS 2.0: an integrated framework for parallel PIC simulations” • Gargaté L, Bingham R, Fonseca R, Silva LO and Bamford R, “dHybrid: a massively parallel kinetic ion fluid electron code for space plasma simulations” 28 th International Conference on Phenomena in Ionized Gases, Prague, Czech Republic, July 2007 • Álvarez R, Marques L and Alves LL, “Two-dimensional modelling of a microwave plasma reactor operated by an axial injection torch”, CD-Proceed. and Book of Abstracts, p. 45 (J. Schmidt, M. Simek, S. Pekárek, V. Prukner, eds.) • Cruz J, Gregório J, Cardoso S, Freitas PP and Alves LL, “Modelling of a radio-frequency ICP-reactor with an ion beam system”, CD-Proceed. and Book of Abstracts, p. 45 (J. Schmidt, M. Simek, S. Pekárek, V. Prukner, eds.) • Felizardo E, Henriques J, Tatarova E, Dias FM and Ferreira CM, “Surface wave driven microwave plasma torch”, 5P09- 47 (J. Schmidt, M. Simek, S. Pekárek, V. Prukner, eds.) • Gordiets B, Tatarova E, Henriques J, Felizardo E, Dias FM, Pinheiro M, Ganachev I and Ferreira CM, “Microwave Air Plasma Torch”, 5P09-42 (J. Schmidt, M. Simek, S. Pekárek, V. Prukner, eds.)