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 INSTR 08 – BINP – Feb. 2008 ION BLOCKING & visible-sensitive gas-PMs A. Lyashenko
Secondary effects in gaseous detectors Gaseous Photo-Multiplier (GPM) Ions secondary e emission feedback pulses gain & performance limitations INSTR 08 – BINP – Feb. 2008 Time Projection Chamber (TPC) Ions dynamic track distortions ION BLOCKING & visible-sensitive gas-PMs A. Lyashenko
IBF: Ion Back-Flow Fraction IBF: The fraction of avalanche-generated ions backflowing 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. INSTR 08 – BINP – Feb. 2008 ION BLOCKING & visible-sensitive gas-PMs A. Lyashenko
Visible-sensitive GPM: Ion-feedback development if - stable operation of visible sensitive GPM Ar/CH 4 (95/5), INSTR 08 – γeff+ ~0. 03, Gain ~ 105 => IBF < 3. 3*10 -4 Visibile-sensitive gas photomultiplier review: M. Balcerzyk et al. , IEEE Trans. Nucl. Sci. Vol. 50 no. 4 (2003) 847 ION BLOCKING & visible-sensitive gas-PMs A. Lyashenko BINP – Feb. 2008
IBF in cascaded GEM GPMs (high Edrift) High Edrift (>0. 5 k. V/cm) needed to efficiently extract photoelectrons Bachman et al. NIMA 438(1999)376 5% @ 0. 5 k. V/cm, Gain ~105 Breskin et al. NIM A 478(2002)225 2 -5%@ 0. 5 k. V/cm, Gain ~105 Bondar et al. NIM A 496(2003)325 3% @ 0. 5 k. V/cm, Gain ~ 105 Need another factor of 100!!! INSTR 08 – BINP – Feb. 2008 ION BLOCKING & visible-sensitive gas-PMs A. Lyashenko
The Microhole & Strip plate (MHSP). Two multiplication stages on a single, double-sided, foil R&D: Weizmann/Coimbra hv photocathode E drift VC-T VA-C A C E trans cathode mesh ~80% of avalanche ions are trapped by cathode strips and plane Veloso et al. Rev. Sci. Inst. A 71 (2000) 237. INSTR 08 – BINP – Feb. 2008 ION BLOCKING & visible-sensitive gas-PMs A. Lyashenko
The benefit of MHSP in a cascade. 3 GEMs+MHSP 4 GEMs IBF: 20% @ Gain > 105 IBF: 3% @ Gain > 105 7 times lower than with cascaded GEMs Mörmann et al. NIM A 516 (2004) 315 INSTR 08 – BINP – Feb. 2008 Maia et al. IEEE NS 49 (2002) Maia et al. NIM A 504(2003)364 ION BLOCKING & visible-sensitive gas-PMs A. Lyashenko
Reverse-biased MHSP (R-MHSP) concept Ions are trapped by negatively biased cathode strips R-MHSP Can trap only ions from successive stages Lyashenko et al. , JINST (2006) 1 P 10004 Lyashenko et al. , JINST (2007) 2 P 08004 INSTR 08 – BINP – Feb. 2008 Flipped-R-MHSP Can trap its own ions Roth, NIM A 535 (2004) 330 Breskin et al. NIM A 553 (2005) 46 Veloso et al. NIM A 548 (2005) 375 ION BLOCKING & visible-sensitive gas-PMs A. Lyashenko
BETTER ION BLOCKING: “COMPOSITE” CASCADED MULTIPLIERS: 1 st R-MHSP or F-R-MHSP: ion defocusing (no gain!) Mid GEMs: gain Last MHSP: extra gain & ion blocking R-MHSP/GEM/MHSP INSTR 08 – BINP – Feb. 2008 F-R-MHSP/GEM/MHSP ION BLOCKING & visible-sensitive gas-PMs A. Lyashenko
IBF in “composite” micro-hole multipliers IBF measured with 100% e-collection efficiency TPC conditions (low drift field) IBF=1. 5*10 -4 @ Gain=104 Gas PMT conditions (high drift field) IBF=3*10 -4 @ Gain=105 IBF is 100 times lower than with 3 GEMs Lyashenko et al. , JINST (2007) 2 P 08004 INSTR 08 – BINP – Feb. 2008 ION BLOCKING & visible-sensitive gas-PMs A. Lyashenko
New ideas for ion blocking Example (R&D in course @ WEIZMANN/COIMBRA ) NEW! “COBRA”: GEM-LIKE PATTERNED ION-SUPPRESSING ELECTRODES (R. d’Oliveira, CERN) INSTR 08 – BINP – Feb. 2008 ION BLOCKING & visible-sensitive gas-PMs A. Lyashenko
IBF suppression with “Cobra” IBF=2. 7*10 -5 Gain=104 IBF=3*10 -6 Gain=105 IBF 1000 times lower than with GEMs, best results ever achieved Though, presently at the expense of electron collection (~20%) INSTR 08 – BINP – Feb. 2008 ION BLOCKING & visible-sensitive gas-PMs A. Lyashenko
IBF reduction summary TPC (Edrift=0. 1 -0. 2 k. V/cm, Gain=104) GPM (Edrift=0. 5 k. V/cm, Gain=105) Detector type IBF Collection efficiency 3 GEM 0. 5% 100% 5% (20%)* 100% 4 GEM 100% 2% (0. 01%)** 100% R-MHSP/ 0. 08% GEM/MHSP 100% 0. 1% 100% F-R-MHSP/ 0. 015% GEM/MHSP 100% 0. 03% 100% “Cobra”/ 2 GEM 20% 0. 0003% 20% 0. 0027% * Reflective PC INSTR 08 – BINP – Feb. 2008 **Gated mode ION BLOCKING & visible-sensitive gas-PMs A. Lyashenko
Visible-sensitive GPM Test detector setup UHV compatible materials Sealed detector Bi-alkali PC Base plate made in Novosibirsk INSTR 08 – BINP – Feb. 2008 ION BLOCKING & visible-sensitive gas-PMs A. Lyashenko
Visible-sensitive GPM: Gain Divergence Gmeas G 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 INSTR 08 – BINP – Feb. 2008 ION BLOCKING & visible-sensitive gas-PMs A. Lyashenko
Gated operation of visible-sensitive GPM Ion gating electrode Gain~106 GATED MULTI-GEM GAIN: ~100 in DC mode (ion feedback limit), IBF~10% ~106 in ion-gating mode; IBF~10 -4 A. Breskin et al. NIM A 553 (2005) 46 -52 INSTR 08 – BINP – Feb. 2008 ION BLOCKING & visible-sensitive gas-PMs A. Lyashenko
DC operation of visible-sensitive GPM Flipped Cobra + 2 GEMs K-Cs-Sb Gain~105 Cs. I K-Cs-Sb DC Gain limit~100 in cascaded GEMs Gain >105 in DC mode single photon sensitivity First evidence of DC high gain operation of visible-sensitive GPM INSTR 08 – BINP – Feb. 2008 ION BLOCKING & visible-sensitive gas-PMs A. Lyashenko
DC operation of visible-sensitive GPM 2 GEMs + Cobra + GEM K-Cs-Sb Gain~104 Cs. I Gain ~104 at full collection efficiency for photoelectrons IBF=7*10 -3@Gain=104 was not optimized INSTR 08 – BINP – Feb. 2008 ION BLOCKING & visible-sensitive gas-PMs A. Lyashenko
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 >105 reached with visible-sensitive K-Cs-Sb PC with full efficiency for collecting primary electrons – Gain ~104 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 INSTR 08 – BINP – Feb. 2008 ION BLOCKING & visible-sensitive gas-PMs A. Lyashenko
Additional slides INSTR 08 – BINP – Feb. 2008 ION BLOCKING & visible-sensitive gas-PMs A. Lyashenko
Auger neutralization process • Ei is the potential energy of the ion • Epe the photoemission threshold, • E 1 and E 2 are the potential energy of the photocathode electrons that participate in the process, and • Ekin the kinetic energy of the emitted secondary electron. Condition for the secondary electron emission: Ei>2 Epe (K 2 Sb. Cs)=2 e. V, while Ei=(CH 4)=12. 6 e. V INSTR 08 – BINP – Feb. 2008 ION BLOCKING & visible-sensitive gas-PMs A. Lyashenko
Charge exchange in 700 Torr Ar/CH 4(95/5) 0. 5 cm It takes 100 – 1000 collisions for Ar + + CH 4 Ar + CH 4+ Mean free path ~10 -5 cm at normal conditions Only CH 4+ remain after 10 -3/p – 10 -2/p cm (p=0. 05 => 0. 02 – 0. 2 cm) of drift INSTR 08 – BINP – Feb. 2008 ION BLOCKING & visible-sensitive gas-PMs A. Lyashenko
K-Cs-Sb stability in gas INSTR 08 – BINP – Feb. 2008 ION BLOCKING & visible-sensitive gas-PMs A. Lyashenko
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