Efficient ion blocking in gaseous detectors and its application to visible-sensitive gaseous photomultipliers A. Breskin, A. Lyashenko and R. Chechik Weizmann Institute of Science, Rehovot, Israel & J. M. F. dos Santos, F. D. Amaro and J. F. C. A. Veloso University of Coimbra, Portugal RD 51 Amsterdam 4/08 ION BLOCKING & visible-sensitive gas-PMs A. Breskin
Secondary effects in gaseous detectors Gaseous Photo-Multiplier (GPM) Ions secondary e emission feedback pulses gain & performance limitations RD 51 Amsterdam 4/08 Time Projection Chamber (TPC) Ions dynamic track distortions ION BLOCKING & visible-sensitive gas-PMs A. Breskin
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. RD 51 Amsterdam 4/08 ION BLOCKING & visible-sensitive gas-PMs A. Breskin
Visible-sensitive gaseous photomultipliers: Ion-feedback development geff : ion feedback coeff. if - stable operation of visible sensitive GPM Ar/CH 4 (95/5), RD 51 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 Amsterdam 4/08 A. Breskin
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!!! RD 51 Amsterdam 4/08 ION BLOCKING & visible-sensitive gas-PMs A. Breskin
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. RD 51 Amsterdam 4/08 ION BLOCKING & visible-sensitive gas-PMs A. Breskin
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 RD 51 Amsterdam 4/08 Maia et al. IEEE NS 49 (2002) Maia et al. NIM A 504(2003)364 ION BLOCKING & visible-sensitive gas-PMs A. Breskin
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 RD 51 Amsterdam 4/08 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. Breskin
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 RD 51 Amsterdam 4/08 F-R-MHSP/GEM/MHSP ION BLOCKING & visible-sensitive gas-PMs A. Breskin
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 RD 51 Amsterdam 4/08 ION BLOCKING & visible-sensitive gas-PMs A. Breskin
New ideas for ion blocking R&D in course @ WEIZMANN/COIMBRA ) NEW! “COBRA”: GEM-LIKE PATTERNED ION-SUPPRESSING ELECTRODES (R. d’Oliveira, CERN) RD 51 Amsterdam 4/08 ION BLOCKING & visible-sensitive gas-PMs A. Breskin
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%) RD 51 Amsterdam 4/08 ION BLOCKING & visible-sensitive gas-PMs A. Breskin
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 RD 51 Amsterdam 4/08 **Gated mode ION BLOCKING & visible-sensitive gas-PMs A. Breskin
Visible-sensitive GPM Test detector setup UHV compatible materials Sealed detector Bi-alkali PC Base plate made in Novosibirsk RD 51 Amsterdam 4/08 ION BLOCKING & visible-sensitive gas-PMs A. Breskin
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 RD 51 Amsterdam 4/08 ION BLOCKING & visible-sensitive gas-PMs A. Breskin
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 RD 51 Amsterdam 4/08 ION BLOCKING & visible-sensitive gas-PMs A. Breskin
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 But: e- collection efficiency ~ 20% RD 51 Amsterdam 4/08 ION BLOCKING & visible-sensitive gas-PMs A. Breskin
DC operation of F-R-MHSP/GEM/MHSP with K-Cs-Sb photocathode Gain ~105 at full photoelectron collection efficiency First evidence of DC high gain operation of visible-sensitive GPM RD 51 Amsterdam 4/08 ION BLOCKING & visible-sensitive gas-PMs A. Breskin
Summary Cascaded Patterned Hole Multipliers (PHM) significant improvement in ion blocking in gaseous detectors of importance in: Tracking detectors (TPC) & Gaseous Photomultipliers with MHSP/GEM-based CASCADED MULTIPLIERS • • 100 times lower IBF than with cascaded GEMs with full efficiency for collecting primary electrons! Gain >105 reached with visible-sensitive K-Cs-Sb PC with Cobra/GEM-based CASCADED MULTIPLIERS • • 1000 times lower IBF than with cascaded GEMs with so-far low e- collection efficiency – Gain >105 reached with visible-sensitive K-Cs-Sb PC First evidence of high-gain DC operation of visible-sensitive GPM Further work: • • Optimization of COBRA Double-sided patterned hole-multipliers RD 51 Amsterdam 4/08 ION BLOCKING & visible-sensitive gas-PMs A. Breskin
K-Cs-Sb stability in gas RD 51 Amsterdam 4/08 ION BLOCKING & visible-sensitive gas-PMs A. Breskin
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