1. A. Lyashenko INSTR08 – BINP – Feb. 2008 ION BLOCKING & visible-sensitive gas-PMs Efficient ion blocking in gaseous detectors and its application to visible-sensitive gas-avalanche photomultipliers A. Lyashenko, A. Breskin and R. Chechik Weizmann Institute of Science, Rehovot, Israel And J.M.F. dos Santos, F.D. Amaro and J.F.C.A. Veloso University of Coimbra, Portugal

2. A. Lyashenko INSTR08 – BINP – Feb. 2008 ION BLOCKING & visible-sensitive gas-PMs Secondary effects in gaseous detectors Gaseous Photo-Multiplier (GPM) Time Projection Chamber (TPC) Ions   secondary e emission  ion feedback pulses  gain & performance limitations Ions   dynamic track distortions

3. A. Lyashenko INSTR08 – BINP – Feb. 2008 ION BLOCKING & visible-sensitive gas-PMs IBF: Ion Back-Flow Fraction IBF: The fraction of avalanche-generated ions back- flowing to the drift region or to the photocathode  Major efforts to limit ion backflow 1. GATING  operation in “gated-mode”  deadtime, trigger - - 2. NEW e - - MULTIPLIERS  operation in DC mode (cascaded-GEM*, MICROMEGAS…&: OTHERS)  Challenge: BLOCK IONS WITHOUT AFFECTING ELECTRON COLLECTION *GEM: Gas Electron Multiplier - Sauli, NIM A 386, (1997) 531.

4. A. Lyashenko INSTR08 – BINP – Feb. 2008 ION BLOCKING & visible-sensitive gas-PMs Visible-sensitive GPM: Ion-feedback development Visibile-sensitive gas photomultiplier review: M. Balcerzyk et al., IEEE Trans. Nucl. Sci. Vol. 50 no. 4 (2003) 847 - stable operation of visible sensitive GPMif Ar/CH 4 (95/5), γ eff + ~0.03, Gain ~ 10 5 => IBF < 3.3*10 -4

5. A. Lyashenko INSTR08 – BINP – Feb. 2008 ION BLOCKING & visible-sensitive gas-PMs IBF in cascaded GEM GPMs (high E drift ) High E drift (>0.5 kV/cm) needed to efficiently extract photoelectrons Bachman et al. NIMA438(1999)376 5% @ 0.5kV/cm, Gain ~10 5 Breskin et al. NIM A478(2002)225 2-5%@ 0.5kV/cm, Gain ~10 5 Bondar et al. NIM A496(2003)325 3% @ 0.5kV/cm, Gain ~ 10 5 Need another factor of 100!!!

6. A. Lyashenko INSTR08 – BINP – Feb. 2008 ION BLOCKING & visible-sensitive gas-PMs The Microhole & Strip plate (MHSP). ~80% of avalanche ions are trapped by cathode strips and plane Two multiplication stages on a single, double-sided, foil R&D: Weizmann/Coimbra photocathode cathode mesh hv V C-T V A-C E trans E drift CA Veloso et al. Rev. Sci. Inst. A 71 (2000) 237.

7. A. Lyashenko INSTR08 – BINP – Feb. 2008 ION BLOCKING & visible-sensitive gas-PMs IBF: 3% @ Gain > 10 5 IBF: 20% @ Gain > 10 5 The benefit of MHSP in a cascade. Maia et al. IEEE NS49 (2002) Maia et al. NIM A504(2003)364 Mörmann et al. NIM A516 (2004) 315 3GEMs+MHSP 4GEMs 7 times lower than with cascaded GEMs

8. A. Lyashenko INSTR08 – BINP – Feb. 2008 ION BLOCKING & visible-sensitive gas-PMs Reverse-biased MHSP (R-MHSP) concept Flipped-R-MHSPR-MHSP Can trap its own ions Ions are trapped by negatively biased cathode strips Lyashenko et al., JINST (2006) 1 P10004 Lyashenko et al., JINST (2007) 2 P08004 Roth, NIM A535 (2004) 330 Breskin et al. NIM A553 (2005) 46 Veloso et al. NIM A548 (2005) 375 Can trap only ions from successive stages

9. A. Lyashenko INSTR08 – BINP – Feb. 2008 ION BLOCKING & visible-sensitive gas-PMs 1st R-MHSP or F-R-MHSP: ion defocusing (no gain!) Mid GEMs: gain Last MHSP: extra gain & ion blocking BETTER ION BLOCKING: “COMPOSITE” CASCADED MULTIPLIERS: R-MHSP/GEM/MHSPF-R-MHSP/GEM/MHSP

10. A. Lyashenko INSTR08 – BINP – Feb. 2008 ION BLOCKING & visible-sensitive gas-PMs TPC conditions (low drift field) Gas PMT conditions (high drift field) IBF=1.5*10 -4 @ Gain=10 4 IBF=3*10 -4 @ Gain=10 5 Lyashenko et al., JINST (2007) 2 P08004 IBF in “composite” micro-hole multipliers IBF measured with 100% e-collection efficiency IBF is 100 times lower than with 3GEMs

11. A. Lyashenko INSTR08 – BINP – Feb. 2008 ION BLOCKING & visible-sensitive gas-PMs Example (R&D in course @ WEIZMANN/COIMBRA ) NEW! “COBRA”: GEM-LIKE PATTERNED ION-SUPPRESSING ELECTRODES (R. d’Oliveira, CERN) New ideas for ion blocking 

12. A. Lyashenko INSTR08 – BINP – Feb. 2008 ION BLOCKING & visible-sensitive gas-PMs IBF suppression with “Cobra” IBF=2.7*10 -5 Gain=10 4 IBF=3*10 -6 Gain=10 5 IBF 1000 times lower than with GEMs, best results ever achieved Though, presently at the expense of electron collection (~20%)

13. A. Lyashenko INSTR08 – BINP – Feb. 2008 ION BLOCKING & visible-sensitive gas-PMs IBF reduction summary TPC (E drift =0.1-0.2kV/cm, Gain=10 4 ) GPM (E drift =0.5kV/cm, Gain=10 5 ) Detector type IBFCollection efficiency IBFCollection efficiency 3GEM0.5%100%5% (20%) * 100% 4GEM100%2% (0.01%) ** 100% R-MHSP/ GEM/MHSP 0.08%100%0.1%100% F-R-MHSP/ GEM/MHSP 0.015%100%0.03%100% “Cobra”/ 2GEM 0.0027%20%0.0003%20% * Reflective PC **Gated mode

14. A. Lyashenko INSTR08 – BINP – Feb. 2008 ION BLOCKING & visible-sensitive gas-PMs Sealed detector Test detector setup Base plate made in Novosibirsk Visible-sensitive GPM UHV compatible materials Bi-alkali PC

15. A. Lyashenko INSTR08 – BINP – Feb. 2008 ION BLOCKING & visible-sensitive gas-PMs Visible-sensitive GPM: Gain Divergence G G meas K-Cs-Sb, Na-K-Sb, Cs-Sb : Current deviates from exponential Max Gain ~ few 100, IBF~10% D. Mörmann et al.,NIM A 504 (2003) 93

16. A. Lyashenko INSTR08 – BINP – Feb. 2008 ION BLOCKING & visible-sensitive gas-PMs A.Breskin et al. NIM A553 (2005) 46-52 Gated operation of visible-sensitive GPM GATED MULTI-GEM Gain~10 6 GAIN: ~100 in DC mode (ion feedback limit),IBF~10% ~10 6 in ion-gating mode; IBF~10 -4 Ion gating electrode

17. A. Lyashenko INSTR08 – BINP – Feb. 2008 ION BLOCKING & visible-sensitive gas-PMs DC operation of visible-sensitive GPM First evidence of DC high gain operation of visible-sensitive GPM Gain >10 5 in DC mode  single photon sensitivity K-Cs-Sb Gain~10 5 K-Cs-Sb CsI DC Gain limit~100 in cascaded GEMs Flipped Cobra + 2GEMs

18. A. Lyashenko INSTR08 – BINP – Feb. 2008 ION BLOCKING & visible-sensitive gas-PMs Gain ~10 4 at full collection efficiency for photoelectrons IBF=7*10 -3 @Gain=10 4 was not optimized Gain~10 4 K-Cs-Sb CsI DC operation of visible-sensitive GPM 2GEMs + Cobra + GEM

19. A. Lyashenko INSTR08 – BINP – Feb. 2008 ION BLOCKING & visible-sensitive gas-PMs Summary Cascaded Patterned Hole Multipliers (PHM)  significant improvement in ion blocking in gaseous detectors with MHSP/GEM-based CASCADED MULTIPLIERS 100 times lower IBF than with cascaded GEMs with full efficiency for collecting primary electrons! Not yet investigated with visible-sensitive photocathodes with Cobra/GEM-based CASCADED MULTIPLIERS 1000 times lower IBF than with cascaded GEMs with so-far reduced efficiency for collecting primary electrons –Gain >10 5 reached with visible-sensitive K-Cs-Sb PC with full efficiency for collecting primary electrons –Gain ~10 4 reached with visible-sensitive K-Cs-Sb PC First evidence of high-gain DC operation of visible-sensitive GPM Further work: Operation of MHSP/GEM -based cascaded multiplier with visible PC

20. A. Lyashenko INSTR08 – BINP – Feb. 2008 ION BLOCKING & visible-sensitive gas-PMs Additional slides

21. A. Lyashenko INSTR08 – BINP – Feb. 2008 ION BLOCKING & visible-sensitive gas-PMs Auger neutralization process E i is the potential energy of the ion E pe the photoemission threshold, E 1 and E 2 are the potential energy of the photocathode electrons that participate in the process, and E kin the kinetic energy of the emitted secondary electron. Condition for the secondary electron emission: E i >2E pe E pe (K 2 SbCs)=2eV, while E i =(CH 4 )=12.6 eV

22. A. Lyashenko INSTR08 – BINP – Feb. 2008 ION BLOCKING & visible-sensitive gas-PMs It takes 100 – 1000 collisions for Ar + + CH 4  Ar + CH 4 + Mean free path ~10 -5 cm at normal conditions 0.5cm Charge exchange in 700 Torr Ar/CH 4 (95/5) Only CH 4 + remain after 10 -3 /p – 10 -2 /p cm (p=0.05 => 0.02 – 0.2 cm) of drift

23. A. Lyashenko INSTR08 – BINP – Feb. 2008 ION BLOCKING & visible-sensitive gas-PMs K-Cs-Sb stability in gas