Final Report on the Development of High Brightness Electron Beams for Light Sources

Grant Agreement 101004730 1 / 13 I.FAST Accelerator Research and Innovation for European Science and Society Horizon 2020 Research Infrastructures GA n° 101004730 DELIVERABLE REPORT Final Report on the Development of High Brightness Electron Beams for Light Sources DELIVERABLE: D7.1 Document identifier: IFAST-D7.1 Due date of deliverable: End of Month 48 (April 2025) Report release date: 02/05/2025 Work package: WP7: High Brightness Beams for Light Sources Lead beneficiary: DESY Document status: Final ABSTRACT WP7 aimed at supporting R&D on the production of high brightness electron beams for advanced light sources, with the aim of pushing the performance envelope of the existing state-of-the-art accelerators. The programme covered both storage ring light sources and Linac based Free Electron Lasers. It supported one network activity on ultra-low emittance ring (Task 7.2) and three prototype programmes for hardware subsystem of critical relevance for the new generation of light sources: variable field permanent magnets (Task 7.3), compact C-band RF guns (Task 7.4) and novel Xband structures for compact FELs (Task 7.5). Final Report on the Development of High Brightness Beams for Light Sources Deliverable: D7.1 Date: 02/05/2025 Grant Agreement 101004730 PUBLIC 2 / 13 IFAST Consortium, 2025 For more information on IFAST, its partners and contributors please see https://ifast-project.eu/ This project has received funding from the European Union’s Horizon 2020 Research and Innovation programme under Grant Agreement No 101004730. ARIES began in May 2021 and will run for 4 years. Delivery Slip Name Partner Date Authored by R. Bartolini DESY 14/04/25 Edited by R. Bartolini DESY 02/05/25 Reviewed by D. Alesini [Task coordinator] Y. Papaphilippou [Task coordinator] G. D’Auria [Task coordinator] INFN CERN ELETTRA 02/05/25 Approved by M. Vretenar on behalf of the Steering Committee 02/05/25 Final Report on the Development of High Brightness Beams for Light Sources Deliverable: D7.1 Date: 02/05/2025 Grant Agreement 101004730 PUBLIC 3 / 13 TABLE OF CONTENTS 1. INTRODUCTION ......................................................................................................................................... 4 2. THE ULTRA-LOW EMITTANCE RING NETWORK (TASK 7.2) ....................................................... 6 1.1 SCOPE ................................................................................................................................................................ 6 1.2 ACTIVITIES......................................................................................................................................................... 6 3. THE VARIABLE DIPOLE FOR THE ELETTRA RING (TASK 7.3) ................................................... 7 1.3 SCOPE ................................................................................................................................................................ 7 1.4 ACTIVITIES......................................................................................................................................................... 7 4. THE HIGH GRADIENT C-BAND RF PHOTOCATHODE GUN (TASK 7.4) ..................................... 8 1.5 SCOPE ................................................................................................................................................................ 8 1.6 ACTIVITIES......................................................................................................................................................... 8 5. THE COMPACTLIGHT X-BAND CAVITIES (TASK 7.5) .................................................................. 10 1.7 SCOPE .............................................................................................................................................................. 10 1.8 ACTIVITIES....................................................................................................................................................... 10 6. FUTURE PLANS AND CONCLUSION................................................................................................... 12 7. REFERENCES ............................................................................................................................................ 13 Final Report on the Development of High Brightness Beams for Light Sources Deliverable: D7.1 Date: 02/05/2025 Grant Agreement 101004730 PUBLIC 4 / 13 Executive summary This report summarises the scope and the results of the R&D activities carried out in the WP7: high brightness electron beam for advanced light sources. WP7 consisted of one network on ultra-low emittance rings and three prototypes of critical subsystems for advanced accelerator based light sources. In details, we developed novel magnets structures for ultra-low emittance storage rings (Task 7.3) and novel accelerating structure for LINAC Free Electron Lasers: C-band RF photocathode guns (Task 7.4) and X-band accelerating RF cavities (Task 7.5). The programme was carried out to completion, with milestones and deliverables reached to a very large extent on time, or nearing completion at the time of writing of this report. Task 7.1 concludes its coordination activity with the present report. Task 7.2 oversaw the organization of ten workshops and two experimental sessions. Task 7.3 produced a prototype of a variable field combined function dipole at CIEMAT. Task 7.4 produced two prototypes for C-band RF photocathode guns successfully tested at PSI and Task 7.5 produced a pre-prototype for an X-band RF structure currently under test and a prototype to be assembled in September 2025. 1. Introduction Accelerator based X-ray sources have been a major driver in the development of Photon Science. Particularly the last 10 years have witnessed a wave of storage ring upgrades and green-field projects to design, build and operate ultra-low emittance lattices. Likewise, several new XFEL machines have come in operation. Despite nowadays at least six light sources (MAX IV, SIRIUS, ESRF-EBS, APSU, HEPS and SLS-II) have come in operation, the field is far from saturation, with ever new designs and projects coming up for funding. In this scenario, I-FAST WP7 has supported the networking in the community of accelerators aiming at ultra-low emittance operation, including light sources, HEP colliders and damping rings. Such network was built upon the analogous networks supported by previous EU-funded projects, ARIES and Eucard-2. At the same time, I-FAST WP7 supported also R&D and prototyping in specific technical areas, critical for the development of new, more compact, more efficient high brightness accelerators. Advanced magnet based on permanent magnets were studied and a prototype of a longitudinally variable dipole (Task 7.3) for emittance reduction in storage ring was built for specific application to the ELETTRA 2.0 upgrade. Compact C-band guns were designed and a prototype of a high gradient (160 MV/m) compact RF photocathode guns was built in Task 7.4. X-band cavities for compact Free Electron Lasers were prototyped in Task 7.5. The WP7 programme consisted of six deliverables, listed in Tab. 1 and six milestones, listed in Tab. 2. Final Report on the Development of High Brightness Beams for Light Sources Deliverable: D7.1 Date: 02/05/2025 Grant Agreement 101004730 PUBLIC 5 / 13 Table 1: list of deliverables in WP7 Table 2: list of milestones in WP7 The timeline is reported in Tab. 3. A shift in the deliverables that occurred in Task 7.5 is also highlighted. Deliverable 7.3 was also shifted from M40 to M49. Table 3: timeline for milestones and deliverables of WP7 Final Report on the Development of High Brightness Beams for Light Sources Deliverable: D7.1 Date: 02/05/2025 Grant Agreement 101004730 PUBLIC 6 / 13 2. The Ultra-Low Emittance Ring Network (Task 7.2) 1.1 SCOPE Networking in the community of ultra-low emittance rings has been supported with the organisation of workshops, visit exchange and beam tests. Despite a slow start due to the Corona pandemic, several workshops were held initially on-line, with surprisingly good attendance. General workshops were organised to review the status of the facilities and discuss the latest developments and were complemented by typical workshops, where often very specific aspects (e.g. girder alignment), were discussed by experts drawn from all facilities worldwide. The presentations of the workshops are all available in the corresponding indico pages and a general report on the network was presented at the IPAC24 [1] and was summarised in an I-FAST report (deliverable D7.2). 1.2 ACTIVITIES A full list of workshops and experimental tests is reported below: • 10th-11th May 2021 (DESY/Virtual): Mini-workshop on girders and alignment, ~80 participants, https://indico.desy.de/event/30022/ • 25th-29th April 2022 (KIT): Beam diagnostics and dynamics in low emittance rings, 81 registered, https://indico.scc.kit.edu/event/2592/overview • 26th-29th June 2022 (ALBA): 3rd workshop on low emittance ring design, ~60 participants https://indico.cells.es/event/1072/ • 26th-29th April 2023 (DESY): support for the Pulse POwer for Kicker System (PulPOKS), ~35 participants, https://indico.cern.ch/event/1243048/ • 1st-2nd June 2023 (DESY): Resistive magnets for ultra-low emittance rings, ~50 participants, https://indico.desy.de/event/39184/ • 14-15th November 2023 (Trieste): Permanent magnet based solution for low emittance rings (joint with LEAPS), 42 participants, https://indico.cells.es/event/1373/ • 13-16th February 2024 (CERN): 9th general workshop ultra-low emittance rings, ~100 participants, https://indico.cern.ch/event/1326603/ • 3-6th March 2024 (KIT): topical workshop on feedback systems and related beam dynamics, 43 participants, https://indico.scc.kit.edu/event/3742/ • 7-8th March 2024 (KIT): topical workshop on injectors for ultra low emittance rings, 41 participants, https://indico.scc.kit.edu/event/3948/ • 17th-20th September 2024 (PSI, Bern): topical workshop on Longitudinal Electron beam Dynamics for Coherent Light Sources (LEDS 2024), ~36 participants, https://indico.psi.ch/event/15973/ • 17th-19th March 2024 (KIT): topical workshop on Stability of Storage Ring based Light Sources, ~120 participants, https://indico.scc.kit.edu/event/4809/ Final Report on the Development of High Brightness Beams for Light Sources Deliverable: D7.1 Date: 02/05/2025 Grant Agreement 101004730 PUBLIC 7 / 13 In preparation • 10th Low Emittance Ring General Workshop, (TBD) Two experimental sessions were organized at KARA as follow up of two workshops • 3-6th March 2024 (KIT): feedback systems measurements • 19th-20st March 2024 (KIT, Karlsruhe): beam-based alignment and beam stability under varying thermal load. 3. The Variable Dipole for the ELETTRA Ring (Task 7.3) 1.3 SCOPE One of the main routes to reduce the emittance in a storage ring is the control of the dipole field in the main dipoles, to optimally match the dispersion function and reduce the contribution of the radiation integral I5 to the equilibrium emittance. In this context, Task 7.3 optimised the longitudinal profile of the combined function dipole to reduce the emittance of the newly proposed upgrade of the ELETTRA storage ring. The combined function dipole is built with permanent magnets hence reducing the power consumption of the ring, removing the need of cooling circuits hence improving the stability of the magnet. The programme of Task 7.3 consisted in the beam dynamic studies to optimise the dipole profile and the construction of the prototype, hence including magnetic design, mechanical design, construction and final magnetic measurements. 1.4 ACTIVITIES Building on previous studies for the CLIC damping rings [2] the dipole field profile was optimised providing a reduction of the ELETTRA 2.0 ring emittance from the nominal 212 pm to 100 pm [3]. A plot of the expected longitudinal distribution of the magnetic field is shown in Fig. 1. Fig. 1: longitudinal profile of the dipole field and of the quadrupole component Final Report on the Development of High Brightness Beams for Light Sources Deliverable: D7.1 Date: 02/05/2025 Grant Agreement 101004730 PUBLIC 8 / 13 The magnetic and mechanical design was carried out at CIEMAT taking full profit of the lesson learnt from the prototype built for the CLIC damping ring. NdFeB was preferred to the more commonly used SmCo, allowing to exceed the specifications required in terms of peak field (2.3 T) and maximum gradient (23 T/m) with a vertical gap of 18mm. A CAD model of the prototype is shown in Fig. 2. Fig. 2. CAD model of the VADER prototype built at CIEMAT The prototype will be produced starting in April 2025 by Kyma (Deliverable 7.3) and it will be measured at the ELETTRA magnetic benches in September 2025. 4. The high gradient C-band RF photocathode gun (Task 7.4) 1.5 SCOPE In order to reduce the size of LINAC system for X-ray Free electron lasers, the use of C-Band technology has been pioneered at SACLA in Japan. The interest in reducing also the injector, and the higher gradients achievable, brought to consider C-band solutions also for the RF photocathode gun. The programme of Task 7.4 consisted in the design, construction and comparison of two C-band RF gun prototypes, a standing wave gun (SW) and a travelling wave gun (TW). 1.6 ACTIVITIES The SW gun prototype was designed at INFN, Frascati. The construction was carried out at COMEB. The low power tests have been performed at INFN and the high-power tests were done at PSI. Final Report on the Development of High Brightness Beams for Light Sources Deliverable: D7.1 Date: 02/05/2025 Grant Agreement 101004730 PUBLIC 9 / 13 The TW gun prototype was designed at PSI. The construction of the cell and couplers was carried out at VLD, the final brazing has been done at PSI. RF tests were also done at PSI. The layout and field distribution obtained in RF simulations of the SW structure is shown in Fig. 3 Fig. 3: RF design and field distribution of the SW C-Band gun The SW RF photo-gun was produced by June 2023 and high-power RF test started at PSI in December 2023 [4]. The field gradient exceeded 160 MV/m (Milestone M29). Fig. 4: C-Band SW RF gun installed at PSI High-Power RF test-stand. The TW prototype was completed in August 2024 and high-power RF test started in January 2025 and are still ongoing. So far, a peak gradient of 147 MV/m has been achieved (Milestone M29).