1. 1 CPPM Test bench for photon detectors Imen Al Samarai*, Jose Busto, Anne-Gaelle Dehaine (Photonis),Greg Hallewell Pascale Keller & Thierry LeGou Developed as part of contract with Photonis for R&D on Crystal Hybrid Photo Detectors * PhD student co-financed by CPPM/Photonis KM3NeT Workpackage meeting, Paris, Feb 23-24, 2009

2. 2 X-HPD: Optical sensor already used in neutrino telescopes Philips/Photonis XP 2600 Quasar-370X-HPD CERN (C2GT) Dumand 15’’ P47 (Y 2 Si O 5 :Ce) phosphor powder XP 2982 - 11 stages Baikal: 200 deployed 15’’ P47 phosphor+ YSO UGON – 12/ 13 stages In development 8’’ LYSO (conical) XP 3102 - 11 stages Telescope Diameter Geometry Scintillator PM Modèles à simuler 2

3. 3 X-HPD: Optical sensor already used in neutrino telescopes Le XP 2600X-HPD CERN Expérience Dumand 15’’ P47 (Y 2 Si O 5 :Ce) XP 2982 - 11 stages Expérience Baikal 15’’ P47 et bloc cristal YSO En développement 8’’ Cristal LYSO conique XP 3102 - 11 stages Telescope Diameter Geometry Scintillator PM Modèles à simuler 3 Average Q.E.: 41% Standard bialkali

4. Further comments on QE of reflective mode photocathode Semitransparent UBA cathodes now clawing 40-45%: not much more headroom - 50% a natural limit, since no significant electric field (< 100V/cm) inside the cathode bulk in a standard large hemispherical PM  p.e. extraction by random walk with 50% p.e.’s walking to wrong hemisphere; QE Reflective photocathodes have higher QE than semi-transparent (CsI – GEM experience) Can be deposited ‘for free’ on aluminium photocathode equipotential conductor surface - which serves no useful detection function in a large PMT - In a focussed X-HPD can trade some extra solid angle coverage for much greater QE in sensitive solid angle zone: Al layer keeps more photons in photocathode Extraction field >> than in large hemi. PM Significant P/V degredation (probably also pre-pusing and after-pulsing) in SBiAl cf standard BiAl

5. 5 XP2600 (Dumand) Quasar-370 (Baikal- NT200) Hamamatsu R7081-20 (PM ANTARES) Overall collection efficiency (Quantum + electrostatic) 100% 80% TTS (FWHM)<5 ns2 ns2.5 ns Pre-pulses late pulses None After pulse II <1% None After pulse II <1% Prepulse 0.01% Afterpulse II 3.8% Terrestrial B-field immunity Insensitive (25kV accelerating field) Needs mu-metal cage Multi-photon charge spectrum du Quasar-370 Charge spectrum of R7081-20 Advantages compared to standard hemispherical PMTs 5 X-HPD: Optical sensor already used in neutrino telescopes

6. 6 CPPM Test bench for photon detectors Tests on X-HPD prototypes Simulations with Simion8 (electrostatics) Near future developments

7. 7 3 Photonis 8’’ X-HPDs with 4 cm Ø metal plate anodes delivered for photocathode mapping All glass envelopes, internal photocathode deposition, 2 polar angle ranges: VERY IMPORTANT TO NOTE THAT PHOTOCATHODE IS PARTLY DEPOSITED ON ALUMINIUM (WHICH IMPROVES Q.E. IN REFLECTIVE MODE) 3 prototypes: - SN05 et SN07: AOV ~ 46° -SN08: AOV ~ 68° -SN08: AOV ~ 68° Prototypes 5 & 7Prototype 8Angle of view definition

8. 8 Simulation des trajectoires électroniques ModèlesÉquipotentielles et temps de transit Quasar-370 D= 37 cm X-HPD CERN D= 20 cm X-HPD Photonis D= 20 cm 2 * TT modèles Les résultats

9. 9 Simulation des trajectoires électroniques ModèlesÉquipotentielles et temps de transit Quasar-370 D= 37 cm X-HPD CERN D= 20 cm X-HPD Photonis D= 20 cm ECBs are extremes, not FWHM,  Les résultats

10. 10 First incarnation of CPPM test bench: photocurrent measurements - Source d’alimentation +/-25 kV - Pico-Ampèrmètre - Résistance 100MΩ en amont de l’Ampermètre

11. 11 Prototype 5 Photocathode cartography Move a (not very focussed) LED in phi, theta : Vacuum attachment with ventouse 1.Double cathode effect seen as polar angle Increases, including contribution by reflection from photocathode deposited on aluminium layer → Increase up to ~80% à theta~40°. 2. Inhomogeneity in phi up to 30%: 3. Excessive current starts in this tube around 1kV (Cesium inter-pin pollution)

12. 12 Prototype 7: Improvement in HV standoff – but takeoff above 6kV Courant d’obscurité en réponse à la tension Au voisinage de 10kV, arc électrique près des pinoches, au niveau du scellement et au niveau du contact verre/métal Interpin geometry still needs work – particularly from point of view of Cesium Augmentation de la tension jusqu’à V- = 10 kV kV nA

13. 13 Prototype 8 Réponse à differents flux – effects of space charge Difficult to measure such low currents : picoammeter cable sensitive to pick-up movements in lab etc… - Saturation for illumination ‘A’  300nA @ à 1500V - Saturation for illumination ‘B’  2 nA @ 50V - Saturation for illumination ‘C’  0.3nA @ 40V TO NOTE: 1nA photocathode current is far from ‘single photon’ conditions: Equivalent to 30 e- in 50ns window

14. 14 Prototype 8 has better HV behaviour than prototype 7: (factor 4 at 10kV) Different tube glass closures with different pinouts kV nA

15. 15 Prototype 8 Photocurrents at different polar angles: constant intensity 472 nm LED H.T. (V) Photocurrent (nA)  =0°  =1 0°  =20°  =40°  =30°

16. 16 Test bench present status Test bench dedicated to phorocathode cartography and ‘double cathode’ effect as a function of theta, phi. → Orthogonal wheels for latitude and longitude –fibreoptic injection from 534 nm laser – which also gives time reference for Transit Time and Transit Time Spread 8” Hamamatsu prototype: super BA 8” Photonis X-HPD with metal anode

17. 17 Labview DAQ system Acquisition in 2GHz digital scope via GPIB (8 bit amplitude)Acquisition in 2GHz digital scope via GPIB (8 bit amplitude) Analysis of TTS w.r.t. external trigger, TOT (FWHM) etc.Analysis of TTS w.r.t. external trigger, TOT (FWHM) etc.

18. 18 Next Steps -First X-HPD prototype with LYSO crystal expected end Feb 2009 (standard bialkali photocathode, internally deposited, all glass envelope); - Photocathode deposited: about to undergo HV testing this week (Feb 24,’09) -Further simulations at Photonis with program that can include dielectric materials (central glass column that supports crystal) and evaluation of resistive degrader coatings; - Collaboration with IPN Orsay for characterisation of crystal decay time, yield etc. in 30kV electron accelerator; - More prototypes with different crystal types, probably convex phosphor deposition during 2009 -Same test bench can be used for standard PMTs: have 3* 8’’ Hamamatsu PMs with super BA photocathode (multi-pulsing characteristics unknown)

19. What is the best/cheapest crystal shape (given that 25kV p.e.’s only penetrate a few microns)

20. What is the best/cheapest crystal shape (given that 25kV p.e.’s only penetrate few  m) GEANT Simulation of photon paths in crystal (n~ 1.8) internal reflection issues

21. Scintillator Considerations SMART and Quasar tubes used YSO phosphor disk: Geometry didn’t allow to exploit full potential. need to use fast 3-D scintillator shape Require high light yield  high gain short decay time Low Z preferable  low back scattering Emission around = 400 nm LY (  / keV)  ns  Z eff  BS emission (nm) emission (nm) YAP:Ce182732~0.35370 LYSO:Ce25~4064~0.45420 LaBr 3 :Ce 633047~0.4360 LaBr 3 is quite hygroscopic Joram, 1 st Photonis prototype for CPPM