A method to stabilise the performance of negatively fed KM3NeT photomultipliers

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A method to stabilise the performance of negatively fed KM3NeT photomultipliers View the table of contents for this issue, or go to the journal homepage for more 2016 JINST 11 P12014 (http://iopscience.iop.org/1748-0221/11/12/P12014) Home Search Collections Journals About Contact us My IOPscience You may also be interested in: The KM3NeT neutrino telescope R Coniglione and KM3NeT collaboration KM3NeT: designing a cubic-kilometre scale neutrino telescope for the mediterranean J Perkin and L F Thompson Solar neutrino problem still perplexes Dave Wark KM3NeT - ORCA: measuring the neutrino mass ordering in the Mediterranean Antoine Kouchner High energy neutrino detection with KM3NeT Pasquale Migliozzi and KM3NeT Collaboration Photon detection efficiency measurements of the VERITAS Cherenkov telescope photomultipliers after four years of operation E. Gazda, T. Nguyen, N. Otte et al. Status of the KM3NeT project A Margiotta Very low power, high voltage base for a Photo Multiplier Tube for the KM3NeT deep sea neutrino telescope P Timmer, E Heine and H Peek Progress and latest results from Baikal, Nestor, NEMO and KM3NeT Emilio Migneco 2016 JINST 11 P12014 Published by IOP Publishing for Sissa Medialab Received:September 23, 2016 Revised:November 1, 2016 Accepted:November 30, 2016 Published:December 19, 2016 A method to stabilise the performance of negatively fed KM3NeT photomultipliers The K3MNet collaboration S. Adrián-Martínez,am M. Ageron,bS. Aiello,sA. Albert,an F. Ameli,wE. G. Anassontzis,ad M. Andre,al G. Androulakis,ab M. Anghinolfi,tG. Anton,gM. Ardid,am T. Avgitas,c G. Barbarino,u,ai E. Barbarito,qB. Baret,cJ. Barrios-Martí,kA. Belias,ab E. Berbee,f A. van den Berg,yV. Bertin,bS. Beurthey,bV. van Beveren,fN. Beverini,aj,vS. Biagi,o A. Biagioni,wM. Billault,bM. Bondì,sR. Bormuth,f,zB. Bouhadef,vG. Bourlis,jS. Bourret,c C. Boutonnet,cM. Bouwhuis,fC. Bozza,at R. Bruijn,aq J. Brunner,bE. Buis,ag R. Buompane,u,ae J. Busto,bG. Cacopardo,oL. Caillat,bM. Calamai,vD. Calvo,k A. Capone,ak,wL. Caramete,xS. Cecchini,rS. Celli,ak,w,iC. Champion,cS. Cherubini,o,ar V. Chiarella,pL. Chiarelli,r,nT. Chiarusi,rM. Circella,qL. Classen,gD. Cobas,c R. Cocimano,oJ.A.B. Coelho,cA. Coleiro,cS. Colonges,cR. Coniglione,oM. Cordelli,p A. Cosquer,bP. Coyle,bA. Creusot,cG. Cuttone,oC. D’Amato,oA. D’Amico,f A. D’Onofrio,u,ae G. De Bonis,wC. De Sio,at F. Di Capua,uI. Di Palma,ak,wC. Distefano,o C. Donzaud,cD. Dornic,bQ. Dorosti-Hasankiadeh,yE. Drakopoulou,ab D. Drouhin,an M. Durocher,o,iT. Eberl,gS. Eichie,g,hD. van Eijk,fI. El Bojaddaini,ao D. Elsaesser,au A. Enzenhöfer,bM. Favaro,r,nP. Fermani,wG. Ferrara,o,ar G. Frascadore,oM. Furini,r L.A. Fusco,r,ah T. Gal,gS. Galatà,cF. Garufi,u,ai P. Gay,c,mM. Gebyehu,fF. Giacomini,r,n L. Gialanella,u,ae V. Giordano,sN. Gizani,jR. Gracia,cK. Graf,gT. Grégoire,cG. Grella,at A. Grmek,oM. Guerzoni,rR. Habel,pS. Hallmann,gH. van Haren,ac S. Harissopulos,ab T. Heid,gA. Heijboer,fE. Heine,fS. Henry,bJ.J. Hernández-Rey,kM. Hevinga,y J. Hofestädt,gC.M.F. Hugon,tG. Illuminati,kC.W. James,gP. Jansweijer,fM. Jongen,f M. de Jong,fM. Kadler,au O. Kalekin,gA. Kappes,gU.F. Katz,gP. Keller,bG. Kieft,f D. Kießling,gE.N. Koffeman,fP. Kooijman,aq,av A. Kouchner,cM. Kreter,au V. Kulikovskiy,b R. Lahmann,gP. Lamare,bA. Leisos,jE. Leonora,sM. Lindsey Clark,cA. Liolios,d C.D. Llorens Alvarez,am D. Lo Presti,sH. Löhner,yA. Lonardo,wM. Lotze,kS. Loucatos,c E. Maccioni,aj,vK. Mannheim,au M. Manzali,r,nA. Margiotta,r,ah A. Margotti,rA. Marinelli,a j,v Published under the terms of the Creative Commons Attribution 3.0 License by IOP Publishing Ltd and Sissa Medialab srl. Any further distribution of this work must maintain attribution to the author(s) and the published article’s title, journal citation and DOI. doi:10.1088/1748-0221/11/12/P12014 2016 JINST 11 P12014 O. Mariş,xC. Markou,ab J.A. Martínez-Mora,am A. Martini,pF. Marzaioli,u,ae R. Mele,u,ai K.W. Melis,fT. Michael,fP. MigliozziuE. Migneco,oP. Mijakowski,aa A. Miraglia,o C.M. Mollo,uM. Mongelli,qM. Morganti,v,aA. Moussa,ao P. Musico,tM. Musumeci,o C.A. Nicolau,wI. Olcina,kC. Olivetto,cA. Orlando,oA. Orzelli,tG. Pancaldi,rA. Paolucci,r A. Papaikonomou,jR. Papaleo,oG.E. Păvălaş,xH. Peek,fG. Pellegrini,rC. Pellegrino,r,ah C. Perrina,ak,wM. Pfutzner,fP. Piattelli,oK. Pikounis,ab G.E. Poma,o,ar V. Popa,xT. Pradier,l F. Pratolongo,tG. Pühlhofer,eS. Pulvirenti,oL. Quinn,bC. Racca,an F. Raffaelli,v N. Randazzo,sD. Real,kL. Resvanis,ad J. Reubelt,gG. Riccobene,oC. Rossi,tA. Rovelli,o M. Saldaña,am I. Salvadori,bD.F.E. Samtleben,f,zA. Sánchez García,kA. Sánchez Losa,q M. Sanguineti,tA. Santangelo,eD. Santonocito,oP. Sapienza,oF. Schimmel,f J. Schmelling,fJ. Schnabel,gV. Sciacca,oM. Sedita,oT. Seitz,gI. Sgura,qF. Simeone,w V. Sipala,sB. Spisso,at,uM. Spurio,r,ah G. Stavropoulos,ab J. Steijger,fS.M. Stellacci,at D. Stransky,gM. Taiuti,t,as Y. Tayalati,ao,ap F. Terrasi,u,ae D. Tézier,bS. Theraube,b P. Timmer,fC. Tönnis,kL. Trasatti,pR. Travaglini,rA. Trovato,oA. Tsirigotis,jS. Tzamarias,d E. Tzamariudaki,ab B. Vallage,cV. Van Elewyck,cJ. Vermeulen,fF. Versari,r,ah P. Vicini,w S. Viola,oD. Vivolo,u,ai M. Volkert,gL. Wiggers,fJ. Wilms,hE. de Wolf,f,aq K. Zachariadou,a f S. Zani,r,nJ.D. Zornozakand J. Zúñigak aAccademia Navale di Livorno, Viale Italia 72, Livorno, 57100 Italy bAix-Marseille Université, CNRS/IN2P3, CPPM UMR 7346, 13288, Marseille, France cAPC, Université Paris Diderot, CNRS/IN2P3, CEA/IRFU, Observatoire de Paris, Sorbonne Paris Cité, 75205 Paris, France dAristotle University Thessaloniki, University Campus, Thessaloniki, 54124 Greece eEberhard Karls Universität Tübingen, Institut für Astronomie und Astrophysik, Sand 1, Tübingen, 72076 Germany fFOM, Nikhef, PO Box 41882, Amsterdam, 1098 DB Netherlands gFriedrich-Alexander-Universität Erlangen-Nürnberg, Erlangen Centre for Astroparticle Physics, Erwin-Rommel-Straße 1, 91058 Erlangen, Germany hFriedrich-Alexander-Universität Erlangen-Nürnberg, Remeis Sternwarte, Sternwartstraße 7, 96049 Bamberg, Germany iGran Sasso Science Institute, GSSI, Viale Francesco Crispi 7, L’Aquila, 67100 Italy jHellenic Open University, School of Science / Technology, Natural Sciences, Sahtouri St. / Ag. Andreou St. 16, Patra, 26222 Greece kIFIC - Instituto de Física Corpuscular (CSIC - Universitat de València), c/Catedrático José Beltrán, 2, 46980 Paterna, Valencia, Spain lIN2P3, IPHC, 23 rue du Loess, Strasbourg, 67037 France mIN2P3, LPC, Campus des Cézeaux 24, avenue des Landais BP 80026, Aubière Cedex, 63171 France nINFN, CNAF, v.le C. Berti-Pichat, 6/2, Bologna, 40127 Italy oINFN, Laboratori Nazionali del Sud, Via S. Sofia 62, Catania, 95123 Italy pINFN, LNF, Via Enrico Fermi, 40, Frascati, 00044 Italy qINFN, Sezione di Bari, Via Amendola 173, Bari, 70126 Italy rINFN, Sezione di Bologna, v.le C. Berti-Pichat, 6/2, Bologna, 40127 Italy sINFN, Sezione di Catania, Via Santa Sofia 64, Catania, 95123 Italy tINFN, Sezione di Genova, Via Dodecaneso 33, Genova, 16146 Italy 2016 JINST 11 P12014 uINFN, Sezione di Napoli, Complesso Universitario di Monte S. Angelo, Via Cintia ed. G, Napoli, 80126 Italy vINFN, Sezione di Pisa, Largo Bruno Pontecorvo 3, Pisa, 56127 Italy wINFN, Sezione di Roma, Piazzale Aldo Moro 2, Roma, 00185 Italy xISS, 242, Vacaresti, Bucharest, 40061 Romania yKVI-CART University of Groningen, Groningen, The Netherlands zLeiden University, Leiden Institute of Physics, PO Box 9504, Leiden, 2300 RA Netherlands aaNational Centre for Nuclear Research, 00-681 Warsaw, Poland abNCSR Demokritos, Institute of Nuclear and Particle Physics, Ag. Paraskevi Attikis, Athens, 15310 Greece acNIOZ, PO Box 59, Den Burg, Texel, 1790 AB Netherlands adPhysics Department, N. and K. University of Athens, Athens, Greece aeSeconda Università di Napoli, Dipartimento di Matematica e Fisica, viale Lincoln 5, Caserta, 81100 Italy af Technological Education Institute of Pireaus, Thivon and P. Ralli Str. 250, Egaleo - Athens, 12244 Greece agTNO, Technical Sciences, PO Box 155, Delft, 2600 AD Netherlands ahUniversità di Bologna, Dipartimento di Fisica e Astronomia, v.le C. Berti-Pichat, 6/2, Bologna, 40127 Italy aiUniversità di Napoli “Federico II", Dip. Scienze Fisiche “E. Pancini", Complesso Universitario di Monte S. Angelo, Via Cintia ed. G, Napoli, 80126 Italy aj Università di Pisa, Dipartimento di Fisica, Largo Bruno Pontecorvo 3, Pisa, 56127 Italy ak Università La Sapienza, Dipartimento di Fisica, Piazzale Aldo Moro 2, Roma, 00185 Italy alUniversitat Politècnica de Catalunya, Laboratori d’Aplicacions Bioacústiques, Centre Tecnològic de Vilanova i la Geltrú, Avda. Rambla Exposició, s/n, Vilanova i la Geltrú, 08800 Spain amUniversitat Politècnica de València, Instituto de Investigación para la Gestión Integrada de las Zonas Costeras, C/ Paranimf, 1, Gandia, 46730 Spain anUniversité de Strasbourg, Université de Haute Alsace, GRPHE, 34, Rue du Grillenbreit, Colmar, 68008 France aoUniversity Mohammed I, Faculty of Sciences, BV Mohammed VI, B.P. 717, R.P. 60000 Oujda, Morocco apUniversity Mohammed V in Rabat, Faculty of Sciences, 4 av. Ibn Battouta, B.P. 1014, R.P. 10000 Rabat, Morocco aqUniversity of Amsterdam, Institute of Physics/IHEF, PO Box 94216, Amsterdam, 1090 GE Netherlands ar University of Catania, Dipartimento di Fisica ed Astronomia di Catania, Via Santa Sofia 64, Catania, 95123 Italy asUniversity of Genova, Via Dodecaneso 33, Genova, 16146 Italy at University of Salerno and INFN Gruppo Collegato di Salerno, Department of Physics, Via Giovanni Paolo II 132, Fisciano, 84084 Italy auUniversity Würzburg, Emil-Fischer-Straße 31, Würzburg, 97074 Germany avUtrecht University, Department of Physics and Astronomy, PO Box 80000, Utrecht, 3508 TA Netherlands E-mail: [email protected] 2016 JINST 11 P12014 Abstract: The KM3NeT research infrastructure, currently under construction in the Mediterranean Sea, will host neutrino telescopes for the identification of neutrino sources in the Universe and for studies of the neutrino mass hierarchy. These telescopes will house hundreds of thousands of photomultiplier tubes that will have to be operated in a stable and reliable fashion. In this context, the stability of the dark counts has been investigated for photomultiplier tubes with negative high voltage on the photocathode and held in insulating support structures made of 3D printed nylon material. Small gaps between the rigid support structure and the photomultiplier tubes in the presence of electric fields can lead to discharges that produce dark count rates that are highly variable. A solution was found by applying the same insulating varnish as used for the high voltage bases directly to the outside of the photomultiplier tubes. This transparent conformal coating provides a convenient and inexpensive method of insulation. Keywords: Instrument optimisation; Large detector systems for particle and astroparticle physics; Neutrino detectors; Photon detectors for UV, visible and IR photons (gas) (gas-photocathodes, solid-photocathodes) 2016 JINST 11 P12014 Contents 1 Introduction 1 2 The measurement setup 2 3 Study of the anomalous dark count rates 3 4 PMT insulation by using transparent conformal coating: tests and results 6 5 Conclusion 7 1 Introduction The stability of photomultiplier tubes (PMTs) is strongly influenced by electric fields. In particular, electric fields generated in the glass envelope or close surroundings of the PMT are often responsible for erratic and unstable behaviour. PMTs can be operated with a positive or a negative high voltage. The use of positive high voltage implies that the cathode is at ground potential. In this case, in order to have no field gradient and good performance it is sufficient to keep the glass case of the PMT and the material in contact with ground potential. Therefore, positive high voltage is usually the preferred mode of PMT operation [1,2]. However, for applications with the anode directly coupled to an external circuit, the use of negative high voltage is convenient. In this case, optimal and stable performance can be obtained provided that precautions are taken to eliminate electric fields in the vicinity of the PMT. Several solutions can be adopted to overcome this problem such as wrapping the PMT glass envelope with insulating tape or connecting any external conductor in contact with the PMT window or the glass envelope to cathode potential. Only good insulators should be brought into direct contact with the PMT. These precautions, although useful, have some drawbacks: wrapping insulating tape is time consuming and the connection of all surrounding materials to cathode potential implies a more complicated structure of the PMT holder. This is the challenge for the design of the KM3NeT optical modules. KM3NeT [3] is a research infrastructure hosting the ARCA and ORCA telescopes in the Mediterranean Sea, dedicated to the identification of neutrino sources in the Universe and the study of the neutrino mass hierarchy, respectively. The working principle of the telescopes is based on the detection of Cherenkov light in the optically transparent deep-sea water induced by charged particles generated in neutrino interactions. The light is recorded by a large number of PMTs arranged in three-dimensional arrays. The basic detector element of the KM3NeT telescopes is the Digital Optical Module (DOM) [4,5]. It comprises a support structure housing 31 three-inch PMTs within a 432 mm diameter glass sphere, as shown in figure 1, where the support structure is also visible. Since the hundreds of thousands of PMTs of KM3NeT will be fed with negative voltage, a support structure made of nylon has been developed to stabilise their performance. The support structure –1– 2016 JINST 11 P12014 Figure 1. An exploded view of a KM3NeT DOM. A PMT and its support structure are indicated. is manufactured by 3D printing with the selective laser sintering method. The PMT locations are tapered and a silicone O-ring tightly seals around the PMT just below its head. Even though the nylon is an excellent insulator, the dark count rates measured for PMTs (Hamamatsu R12199-02) installed in the support structure were not stable in time and well above the values measured by the vendor. Therefore, a campaign of measurements to understand the origin of the observed anomalous rates and find a remedy against it was initiated. 2 The measurement setup The measurement setup for testing a PMT in its insulating holder inside a light-tight dark box [6] is shown in figure 2. A board dubbed ‘MiniOctopus’ provides the command signals such as the high voltage settings/thresholds and delivers the output signal to an Oscilloscope (Lecroy Wavepro SDA 760Zi). Moreover, the MiniOctopus has the connectors needed to feed 3.3 V to the PMT high voltage base and to the I2C bus. The NI USB-8451 I2C to USB device of National Instruments was used to connect a PC hosting the LabVIEW based software. The dark counts as a function of time are measured using the trigger hold-off feature of the oscilloscope. –2– 2016 JINST 11 P12014 Figure 2. Setup used to measure the PMT dark count rate. Figure 3. Left: schematic of the setup; right: dark count rate measured for a UUT supported by an insulating holder. 3 Study of the anomalous dark count rates To determine the origin of the dark count anomaly, a test experiment with two PMTs arranged as shown in figure 3was performed. Correlations between the anomalous count rates of both PMTs, which could arise either from electrostatic fields or from photons produced somewhere around the PMT, were investigated. The following nomenclature is adopted: UUT (Unit Under Test) is the PMT to be studied; PROBE is the PMT that measures the possible light produced by the UUT. In all configurations the PROBE is a PMT whose dark count rate has been measured to be within the vendor’s specifications. In the first configuration studied, the UUT was a PMT with bare glass tube supported by an insulating frame (see figure 3). The measured dark count rate of the UUT is large and unstable in time as shown in figure 3. –3– 2016 JINST 11 P12014 Figure 4. Count rate measured by the PROBE when the UUT is OFF and switched ON. Figure 5. Left: schematic of the setup; right: count rate measured by the PROBE when the UUT is switched ON and OFF. After 24 hours darkening, the count rate of the PROBE was measured iunder two configurations, the high voltage of the UUT ON and OFF (figure 4). The interesting result is that when the UUT is switched ON the rate of the PROBE increases. As soon as the UUT is switched OFF the count rate goes back to its initial value. The correlation between the high voltage status of the UUT and the measured count rate of the PROBE could arise either from electrostatic fields created once the UUT is switched ON or from photons produced somewhere in the UUT, in particular from discharges in air due to gaps between the glass surface of the UUT and the support. As a test, a thick black paper sheet was interposed between the UUT and the PROBE and the measurement repeated. The results in figure 5no longer show the correlation between the status of UUT and the PROBE count rate. Therefore, it was concluded that the origin of the count rate increase in the PROBE is due to photons produced in or around the UUT. –4–