1. A. BreskinTIPP09 Tsukuba VISIBLE-SENSITIVE GAS-PMs 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 High-gain Gaseous photomultipliers for the visible spectral range Talk dedicated to my friend Georges Charpak Celebrating 85 in March 2009

2. A. BreskinTIPP09 Tsukuba VISIBLE-SENSITIVE GAS-PMs SK  500mm Vacuum PMT Photomultipliers should go flat! Flat, Low cost Bulky, High cost ~11,000 PMTs ~10mm h photocathode Gaseous electron multiplier readout Super Kamiokande NEXT: UNO : 56,650 PMTs Hyper-K : 200,000 PMTs !!!  who can pay?  induced  ring Gaseous PM

3. A. BreskinTIPP09 Tsukuba VISIBLE-SENSITIVE GAS-PMs UV-GPMs used in experiments: ALICE, HADES, COMPASS, J-LAB, PHENIX UV - Gaseous Photomultipliers (GPM) GPM Rev: Chechik & Breskin, NIM A595(2008)116 CERN-ALICE PHENIX Wire-chamber Triple-GEM 400 x 600 mm 2 250 x 250 mm 2 CRYO: Bondar, 2008 JINST 3 P07001 UV photon e-e- readout electrode CsI photocathode THGEM Double-THGEM NEW! Thick-GEM Talk by Chechik

4. A. BreskinTIPP09 Tsukuba VISIBLE-SENSITIVE GAS-PMs Secondary effects in GPMs “open geometry” GPM 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 Hole-multiplier PC h

5. A. BreskinTIPP09 Tsukuba VISIBLE-SENSITIVE GAS-PMs 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-$/cm 2 ) Visible-sensitive GPMs Rev: Chechik & Breskin NIM A 595 (2008) 116 Sealed Triple-GEM with K-Cs-Sb Previous status: bialkali stable under avalanche gas detectors with coated bialkali Sealed triple-GEM with bialkali high gain only in pulsed-gate mode low aging under avalanche MAIN DIFFICULTY: ION FEEDBACK 70μm 50μm GEM: Gas Electron Multiplier Sauli, NIM A 386(1997)531 Balcerzyk, IEEE Trans. Nucl. Sci. Vol. 50 no. 4 (2003) 847

6. A. BreskinTIPP09 Tsukuba VISIBLE-SENSITIVE GAS-PMs Visible-sensitive GPM: Ion-feedback development  stable operation of visible sensitive GPMif CsI K-Cs-Sb K-Cs-Sb, Na-K-Sb, Cs-Sb : Current deviates from exponential Max Gain ~ few 100, IBF~10% G~10 5, γ + eff ?, IBF?

7. A. BreskinTIPP09 Tsukuba VISIBLE-SENSITIVE GAS-PMs IBF depends on effective ion-induced electron emission from PCs PCK-Cs-SbNa-K-Sb IonCH 4 + γ + eff (experimental) 0.03±0.010.02±0.006 γ + eff (theory) 0.0270. 029 PC Ar/CH 4 (95/5), γ eff + ~0.03, Gain ~ 10 5  IBF < 3.3*10 -4  stable operation of visible sensitive GPMif Lyashenko et al, in preparation backscattering on gas molecules Function of E e- (~7eV) Function of: E ion & PC material ( E ion ~13eV for CH 4 + )  extr ~ 7% in Ar/5%CH 4

8. A. BreskinTIPP09 Tsukuba VISIBLE-SENSITIVE GAS-PMs Cascaded-GEM GPMs: high gain but also high ion back-flow Semitransparent GPM Reflective GPM 10 7 10 5 10 3

9. A. BreskinTIPP09 Tsukuba VISIBLE-SENSITIVE GAS-PMs IBF: Ion Back-Flow Fraction IBF: The fraction of avalanche-generated ions back-flowing to the photocathode  Challenge: BLOCK IONS WITHOUT AFFECTING ELECTRON COLLECTION Bachman, NIM A438(1999)376 IBF= 5% Breskin, NIM A478(2002)225 IBF= 2-5% Bondar, NIM A496(2003)325 IBF= 3% @ Edrift 0.5kV/cm, Gain ~10 5 : IBF~5 10 -2  Need another factor of 100!!! IBF

10. A. BreskinTIPP09 Tsukuba VISIBLE-SENSITIVE GAS-PMs operated with ion gating Gaseous detectors with Visible-PC Ion gating NO FEEDBACK ! GATED MULTI-GEM DC: IBF~10 -1 → gain limited to 10 2 Ion gating: IBF~10 -4 → gain ~10 6 Moerman, PhD Thesis, 2005 JINST TH004 Breskin, NIM A553 (2005) 46 10 6 But: gating  dead-time; needs trigger

11. A. BreskinTIPP09 Tsukuba VISIBLE-SENSITIVE GAS-PMs The Microhole & Strip plate (MHSP) Two multiplication stages on a single, double-sided, foil R&D: Weizmann/Coimbra/Aveiro MHSP: Veloso, Rev. Sci. Inst. A 71 (2000) 237 Maia, NIM A A523(2004)334-344 IBF ~ 10 -2 Strips: multiply charges

12. A. BreskinTIPP09 Tsukuba VISIBLE-SENSITIVE GAS-PMs Reverse-biased MHSP (R-MHSP) concept Flipped-Reversed-MHSP (F-R-MHSP) Reversed-MHSP (R-MHSP) Can trap its own ions Ions are trapped by negatively biased cathode strips Lyashenko JINST (2006) 1 P10004 Lyashenko JINST (2007) 2 P08004 Roth, NIM A535 (2004) 330 Breskin NIM A553 (2005) 46 Veloso NIM A548 (2005) 375 Can trap only ions from successive stages Strips: collect ions

13. A. BreskinTIPP09 Tsukuba VISIBLE-SENSITIVE GAS-PMs Lyashenko 2007 JINST 2 P08004 IBF measured with 100% e-collection efficiency IBF=3*10 -4 @ Gain=10 5  100 times lower than 3GEMs 1st R-MHSP or F-R-MHSP: ion defocusing (no gain!) Mid GEMs: gain Last MHSP: extra gain & ion blocking BEST ION BLOCKING: “COMPOSITE” CASCADED MULTIPLIERS: IBF=3*10 -4

14. A. BreskinTIPP09 Tsukuba VISIBLE-SENSITIVE GAS-PMs NEW! “COBRA”: GEM-LIKE PATTERNED ION-SUPPRESSING ELECTRODES New ideas for ion blocking IBF=3*10 -6 Gain=10 5 IBF 1000 times lower than with GEMs; best results ever achieved But: 20% photoelectron collection efficiency… TRYING TO IMPROVE!

15. A. BreskinTIPP09 Tsukuba VISIBLE-SENSITIVE GAS-PMs Sealed detector Test detector setup Visible-sensitive GPM UHV compatible materials Bi-alkali photocathode cascaded multiplier GEM/MHSP

16. A. BreskinTIPP09 Tsukuba VISIBLE-SENSITIVE GAS-PMs Multi-alkali photocathode production (QE 20-40% @ 360-420nm in vacuum for semi-transparent PC) Hot Indium sealing to package @130-150ºC UHV setup for photocathode/detector investigations M. Balcerzyk et al., IEEE TNS Vol. 50 no. 4 (2003) 847 D. Moerman, PhD Thesis 2005 JINST TH 004

17. A. BreskinTIPP09 Tsukuba VISIBLE-SENSITIVE GAS-PMs 20% QE drop @ 2 μC/mm 2 ion charge on photocathode: only ~ 4 x faster drop compared to thin ST CsI (~8 μ C/mm 2 ) K-Sb-Cs PC ageing in avalanche mode Real conditions: gain=10 5 ; IBF=3*10 -4. 20% QE drop 46 years @ 5kHz/mm 2 ph. same conditions with a MWPC (IBF=1)  3000 times shorter lifetime: ~5 days! Breskin NIM A553 (2005) 46 Typical QE of bi-alkali PC produced in our lab vacuum K-Cs-Sb Na-K-Sb Lyashenko et al, in preparation

18. A. BreskinTIPP09 Tsukuba VISIBLE-SENSITIVE GAS-PMs Continuous operation of F-R-MHSP/GEM/MHSP with K-Cs-Sb photocathode with K-Cs-Sb photocathode Gain ~10 5 at full photoelectron collection efficiency First evidence of continuous high gain operation of visible-sensitive GPM K-Cs-Sb CsI 10 5

19. A. BreskinTIPP09 Tsukuba VISIBLE-SENSITIVE GAS-PMs Visible-sensitive GPM features Single photon sensitivity No ion-feedback Fast ns pulses 19 ns 100 photoelectrons Lyashenko et al, JINST, in preparation

20. A. BreskinTIPP09 Tsukuba VISIBLE-SENSITIVE GAS-PMs fresh PC after 14 hours of operation photocathode stability inside UHV preparation chamber Rate: 12kHz/mm 2 photons Gain: 10 5 Total anode charge ~125μC PC is stable in gas in the large vacuum chamber Expected even better stability for sealed devices Kapton  glass? Ceramic? Other? gas Lyashenko et al, JINST, in preparation

21. A. BreskinTIPP09 Tsukuba VISIBLE-SENSITIVE GAS-PMs BACKSCATTERING IN GAS: EFFECTIVE QE Coelho, NIMA 581(2007)190 Breskin, NIM A483 (2002) 670 Dashed-lines are simulation Noble gases Divergence due to scintillation CsI QE eff = QE x transmission (e - extraction efficiency into gas) TRANSMISSIONTRANSMISSION TRANSMISSIONTRANSMISSION transmission Back-scattering h GAS PC

22. A. BreskinTIPP09 Tsukuba VISIBLE-SENSITIVE GAS-PMs Photoelectron transmission from K-Cs-Sb as a function of E-field & photon wavelengths 700 Torr Methane 700 Torr Ar/CH4 (95/5) Higher effective QE at longer WL’s NEW Lyashenko et al, in preparation QE eff = QE x transmission (e - extraction efficiency into gas)

23. A. BreskinTIPP09 Tsukuba VISIBLE-SENSITIVE GAS-PMs Summary Cascaded Patterned Hole Multipliers (MHSP/GEM) RECORD in ion blocking in gaseous detectors, crucial in GPMs 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 10 5 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!