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A. Breskin , A. Lyashenko, R. Chechik Weizmann Institute of Science, Rehovot, Israel

High-gain Gaseous photomultipliers for the visible spectral range. A. Breskin , A. Lyashenko, R. Chechik Weizmann Institute of Science, Rehovot, Israel J.M.F. dos Santos, F.D. Amaro Univ. of Coimbra, Portugal J. F.C.A. Veloso Univ. of Aveiro, Portugal.

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A. Breskin , A. Lyashenko, R. Chechik Weizmann Institute of Science, Rehovot, Israel

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  1. High-gain Gaseous photomultipliers for the visible spectral range A. Breskin, A. Lyashenko, R. Chechik Weizmann Institute of Science, Rehovot, Israel J.M.F. dos Santos, F.D. Amaro Univ. of Coimbra, Portugal J. F.C.A. Veloso Univ. of Aveiro, Portugal Talk dedicated to my friend Georges Charpak Celebrating 85 in March 2009

  2. Photomultipliers should go flat! SK F500mm Vacuum PMT Gaseous PM ~10mm Bulky, High cost hn Flat, Low cost ~11,000 PMTs readout photocathode n-induced m ring Gaseous electron multiplier NEXT: UNO: 56,650 PMTs Hyper-K: 200,000 PMTs !!!  who can pay? Super Kamiokande

  3. UV - Gaseous Photomultipliers (GPM) CsI photocathode UV photon e- THGEM readoutelectrode UV-GPMs used in experiments: ALICE, HADES, COMPASS, J-LAB, PHENIX NEW! Thick-GEM Talk by Chechik CERN-ALICE 400 x 600 mm2 PHENIX 250 x 250 mm2 Double-THGEM Wire-chamber Triple-GEM CRYO: Bondar, 2008 JINST 3 P07001 GPM Rev: Chechik & Breskin, NIM A595(2008)116

  4. E 1e in drift E GEM V D hole + + + E ind >1000e out Secondary effects in GPMs hn “open geometry” GPM Hole-multiplier PC Main problem: Ions & photons   secondary e emission Ion & photon feedback pulses gain & performance limitations • PC masked by electrode • Much lower photon feedback • Lower ion-feedback • better performance

  5. Visible-sensitive GPMs • Motivation for R&D: • large areas • flat geometry (1bar gas) • operation in magnetic fields • sensitivity to single photons • fast (ns) • high localization accuracy (sub-mm) • low cost (dream: few-$/cm2) GEM: Gas Electron Multiplier Sauli, NIM A 386(1997)531 70μm 50μm • Previous status: • bialkali stable under avalanche • gas detectors with coatedbialkali • Sealed triple-GEM with bialkali • high gain only in pulsed-gate mode • low aging under avalanche • MAIN DIFFICULTY: ION FEEDBACK Sealed Triple-GEM with K-Cs-Sb Balcerzyk, IEEE Trans. Nucl. Sci. Vol. 50 no. 4 (2003) 847 Rev: Chechik & Breskin NIM A 595 (2008)116

  6. Visible-sensitive GPM: Ion-feedback development K-Cs-Sb CsI K-Cs-Sb, Na-K-Sb, Cs-Sb : Current deviates from exponential Max Gain ~ few 100, IBF~10% if  stable operation of visible sensitive GPM G~105, γ+eff?, IBF?

  7. IBF depends on effective ion-induced electron emission from PCs PC backscattering on gas molecules Function of Ee- (~7eV) Function of: Eion & PC material (Eion~13eV for CH4+) eextr ~ 7% in Ar/5%CH4 if  stable operation of visible sensitive GPM Ar/CH4 (95/5),γeff+~0.03, Gain ~ 105IBF < 3.3*10-4 Lyashenko et al, in preparation

  8. Cascaded-GEM GPMs: high gain but also high ion back-flow Semitransparent GPM 107 105 103 Reflective GPM

  9. IBF: Ion Back-Flow Fraction IBF: The fraction of avalanche-generated ions back-flowingto the photocathode IBF @ Edrift 0.5kV/cm, Gain ~105 : Bachman, NIM A438(1999)376 IBF= 5% Breskin, NIM A478(2002)225IBF= 2-5% Bondar, NIM A496(2003)325IBF= 3% IBF~5 10-2 Need another factor of 100!!!  Challenge:BLOCK IONS WITHOUT AFFECTING ELECTRON COLLECTION

  10. NO FEEDBACK! Ion gating GATED MULTI-GEM Gaseous detectors with Visible-PC operated with ion gating Moerman, PhD Thesis, 2005 JINST TH004 Breskin, NIM A553 (2005) 46 106 DC: IBF~10-1 → gain limited to 102 Ion gating: IBF~10-4 → gain ~106 But: gating  dead-time; needs trigger

  11. The Microhole & Strip plate (MHSP) Two multiplication stages on a single, double-sided, foil Strips: multiply charges IBF ~ 10-2 R&D: Weizmann/Coimbra/Aveiro MHSP: Veloso, Rev. Sci. Inst. A 71 (2000) 237 Maia, NIM AA523(2004)334-344

  12. Reverse-biased MHSP (R-MHSP) concept Ions are trapped by negatively biased cathode strips Reversed-MHSP (R-MHSP) Strips: collect ions Flipped-Reversed-MHSP (F-R-MHSP) Can trap only ions from successive stages Can trap its own ions Roth, NIM A535 (2004) 330 Breskin NIM A553 (2005) 46 Veloso NIM A548 (2005) 375 Lyashenko JINST (2006) 1 P10004 Lyashenko JINST (2007) 2 P08004

  13. BEST ION BLOCKING: “COMPOSITE” CASCADED MULTIPLIERS: 1st R-MHSP or F-R-MHSP: ion defocusing (no gain!) Mid GEMs:gain Last MHSP: extra gain & ion blocking IBF=3*10-4 IBF measured with 100% e-collection efficiency IBF=3*10-4 @ Gain=105100 times lower than 3GEMs Lyashenko 2007JINST 2 P08004

  14. New ideas for ion blocking NEW!“COBRA”: GEM-LIKE PATTERNED ION-SUPPRESSING ELECTRODES IBF=3*10-6 Gain=105 IBF 1000 times lower than with GEMs; best results ever achieved But: 20% photoelectron collection efficiency… TRYING TO IMPROVE!

  15. Visible-sensitive GPM Bi-alkali photocathode cascaded multiplier UHV compatible materials Test detector setup Sealed detector GEM/MHSP

  16. UHV setup for photocathode/detector investigations • Multi-alkali photocathode production (QE 20-40% @ 360-420nm in vacuum for semi-transparent PC) • Hot Indium sealing to package @130-150ºC M. Balcerzyk et al., IEEE TNS Vol. 50 no. 4 (2003) 847 D. Moerman, PhD Thesis 2005 JINST TH 004

  17. Typical QE of bi-alkali PC produced in our lab Lyashenko et al, in preparation Na-K-Sb K-Cs-Sb vacuum vacuum K-Sb-Cs PC ageing in avalanche mode • 20% QE drop @ 2 μC/mm2 ion charge • on photocathode: • only ~ 4 x faster drop compared to • thin ST CsI (~8 μC/mm2) • Real conditions:gain=105; IBF=3*10-4. • 20% QE drop 46 years @ 5kHz/mm2 ph. • same conditions with a MWPC (IBF=1) •  3000 times shorter lifetime:~5 days! Breskin NIM A553 (2005) 46

  18. Continuous operation of F-R-MHSP/GEM/MHSP with K-Cs-Sb photocathode K-Cs-Sb 105 CsI Gain ~105 at full photoelectron collection efficiency First evidence of continuous high gain operation of visible-sensitive GPM

  19. Visible-sensitive GPM features 100 photoelectrons 19 ns Single photon sensitivity No ion-feedback Fast ns pulses Lyashenko et al, JINST, in preparation

  20. photocathode stability inside UHV preparation chamber fresh PC after 14 hours of operation gas gas PC is stable in gas in the large vacuum chamber Rate: 12kHz/mm2 photons Gain: 105 Total anode charge ~125μC Expected even better stability for sealed devices Kapton  glass? Ceramic? Other? Lyashenko et al, JINST, in preparation

  21. BACKSCATTERING IN GAS: EFFECTIVE QE QEeff = QExtransmission (e- extraction efficiency into gas) hn PC GAS Back-scattering transmission TRANSMISSION Noble gases TRANSMISSION CsI Divergence due to scintillation CsI Dashed-lines are simulation Breskin, NIM A483 (2002) 670 Coelho, NIMA 581(2007)190

  22. Photoelectron transmission from K-Cs-Sb as a function of E-field & photon wavelengths QEeff = QExtransmission (e- extraction efficiency into gas) NEW 700 Torr Methane 700 Torr Ar/CH4 (95/5) Higher effective QE at longer WL’s Lyashenko et al, in preparation

  23. Summary Cascaded Patterned Hole Multipliers (MHSP/GEM) • RECORD in ion blocking in gaseous detectors, crucial inGPMs • IBF~3 10-4 with full photoelectron collection efficiency! • Further improvements in progress (other patterned electrodes) • NEW: Stable visible-sensitive GPM DC-mode operation at 105 Photocathodes • “Reasonable” effective QE in 1 bar gas (18% @ 400nm); can be improved (gas/geometry) Potential applications • Atmospheric-pressure large-area photon detectors! • Potential applications in Particle Physics, Astroparticle, Medical, NDT, etc • Suitable for cryogenic operation (UV GPMs OK) SCIENTIFICALLY FEASABLE  BUT: INDUSTRIAL PROJECT!

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