Ion-induced effects in GEM GEM MHSP- gaseous photomultipliers

Ion-induced effects in GEM & GEM/MHSP- gaseous photomultipliers for the UV & visible spectral range A. Breskin, D. Mörmann, A. Lyashenko and R. Chechik Department of Particle Physics, The Weizmann Institute of Science 76100 Rehovot, Israel F. Amaro, J. Maia, J. Veloso and J. dos Santos Physics Dept. , University of Coimbra, 3004 -516 Coimbra, Portugal http: //www. weizmann. ac. il/home/detlab RICH 04 Mexico A. Breskin

Gaseous Photomultipliers (GPM) Gas 1 atm (F. Piuz et al) Possible solution: closed geometry Cascaded GEM & others photocathode Cs. I on readout pads Problems with wire chambers: open geometry - Photon and ion feedback gain limitations - Damage to the photocathode RICH 04 Mexico I will discuss only our work! A. Breskin

Multi-GEM GPM Semitransparent Photocathode Reflective Photocathode higher QE! • largely reduced photon feedback compared to “open” geometry • no photon feedback • thick pc: easier production • low sensitivity to charged particles! A. Buzulutskov et al. NIM A 443 (2000)164 D. Mörmann et al. NIM A 478 (2002) 230 • high 2 D precision [0. 1 -0. 2 mm] • high gain [>105] single photon sensitivity! • fast signals [ns] good timing RICH 04 Mexico A. Breskin

Multiplication in multi-GEM structures D. Mörmann et al. WIS For a given total gain: a larger number of GEMs permits operation @ lower V HIGHER STABILITY RICH 04 Mexico A. Breskin GEM

Electron transmission into holes high DVGEM VGEM=100 V VGEM=300 V VGEM=500 V E>2 high surface field low backscattering E drift 0. 7 1. 0 1. 4 1. 9 2. 6 3. 7 5. 2 7. 3 10 14 20 k. V/cm Good extraction E GEM => optimal operation at high VGEM RICH 04 Mexico A. Breskin

GPMs: highlights e- Refl. Cs. I, 1 atm CF 4 3 GEM, single electron pulses. 50 m. V gain 105, 10 ns no photon feedback. With reflective PC: low sensitivity to ionizing background radiation - Reflective PC (compared to ST), higher QE, low sensitivity to ionizing BG radiation - High optical opacity of multi-GEM, no photon-feedback - Reduced ion back-flow (compared to MWPC) - Reduced secondary effects high gains 106 - 107 - Operation with large variety of gases, noble gases, CF 4, etc - Fast: with CF 4 RICH 04 Mexico s = 1. 6 ns wsingle electrons s = 0. 33 ns w150 electrons A. Breskin

Examples of GEM-GPM applications • Hadron-Blind Detector (HBD) for PHENIX (I. Tserruya et al. Weizmann) • UV imaging detectors of LXe scintillators for Dark-Matter experiments (XENON, E. Aprile et al. Columbia Univ. ) • UV imaging detectors for a fast LXe Gamma-camera for PET ( D. Thers Nantes/A. B. -Weizmann) RICH 04 Mexico Xe GAS LIQUID Xe GPM LXe A. Breskin

Visible-range Gaseous Photomultipliers UV: established technique various ~“air-stable” photocathodes Real challenge: visible GPMTs for the visible range! Photocathodes(e. g. bi-alkali) are very chemically reactive. Cannot operate in flow-mode! UV Solution: Visible-range GPMTs => sealed mode D. Mörmann et al. NIM A 504 (2003) 93 RICH 04 Mexico A. Breskin

GPMT for visible light sealed 3 Kapton-GEMs & KCs. Sb PC QE in Ar/CH 4 (95/5) ~ 70% of QE in vacuum (backscattering) best expected ~20% @360 -400 nm QE% 15 10 5 300 400 500 / 600 QE in transmissive mode Ar. CH 4 95/5 % Wavelength [nm] 13% = best QE measured after sealing. 2 weeks stability Sealing in gas: In/Sn; 130 -1500 C Sealed detector package with semitransparent K-Cs-Sb PC ~2” Best sealed GPMT: QE = 6% @ 365 nm stable for 1 month under development: Silicon, ceramic Expected higher stability RICH 04 Mexico D. Mörmann et al. NIM A 504 (2003) 93 M. Balcerzyk et al. IEEE TNS 50 (2003) 847 A. Breskin

Gain limitation by ion-feedback No significant feedback observed with Cs. I Significant with efficient secondary electron emitters, e. g. visible photocathodes K-Cs-Sb: Current deviates from exponential 1 atm Ar, 1 GEM ST PC 100 m. V/div 400 ms/div Ion feedback: photocathode-dependent (band gap, electron affinity) gas-dependent (ion species, PC surface processes) field-dependent (ion velocity) Recently measured: SEE Probability = 0. 05 – 0. 5 electron/ion in Ar/CH 4 mixtures (Gas dependent, Ar is worst) RICH 04 Mexico A. Breskin

Drawbacks of ion-photocathode interaction • Secondary avalanches due to ion feedback gain limits, imaging problems (observed in K-Cs-Sb) • Photocathode damage due to ion sputtering observed in both: Cs. I and K-Cs-Sb Major efforts to limit ion backflow RICH 04 Mexico A. Breskin

Ion back-flow in multi-GEM Tracking detectors & TPCs Ed Electron’s path Back-flowing ions Distort the E-field Ion’s back-flow Ed can be kept relatively LOW reduces ion back flow to a few % levels Ed cannot be too low keep e-diffusion low localization resolution S. Bachman et al. NIMA 438(99)376: 5% @ 0. 5 k. V/cm A. Breskin et al. NIM A 478(2002)225 2 -5%@ 0. 5 k. V/cm A. Bondar et al. NIM A 496(2003)325 3%@ 0. 5; 0. 5% @ 0. 1 k. V/cm (GEMs with small holes) RICH 04 Mexico A. Breskin

Ion back-flow in multi-GEM Detectors with solid converters Electron’s path Ion’s back-flow Attempts to reduce the ion back-flow: variables DVGEM ; Etrans ; Eind E @ photocathode must be high for good e-extraction; best @ high VGEM Ion back-flow 10 -20% at best…! (without affecting e- transfer) RICH 04 Mexico D. Mörmann et al. NIM A 516 (2004) 315 A. Breskin

The Microhole & Strip Plate (MHSP) Two multiplication stages on a single, double-sided, foil J. M. Maia et al. IEEE NS 49 (2002) J. M. Maia et al. NIM A 504(2003)364 q Foil: 5 mm copper on both sides of 50 mm Kapton q Bi-conical holes: 50/70 mm (inner/outer) diameter q Anode-strip pattern: 175 mm pitch /15 mm strips q Production: similar to GEM technology (CERN) RICH 04 Mexico R&D in course: Weizmann/Coimbra A. Breskin

Ion back-flow: MHSP vs GEM J. Maia et al. NIM A 523(2004)334 Multi-GEM anode All ions flow back GEM & MHSP A C bottom cathode Some ions flow back but others flow towards the strip cathodes and bottom cathode GEM & MHSP: ion flow reduced to 2 -3% levels! RICH 04 Mexico A. Breskin

MHSP simulation hv photocathode E drift VC-T VA-C A C E trans cathode mesh RICH 04 Mexico Simulations: Oleg Bouianov A. Breskin

The multi-GEM & MHSP photomultiplier J. Maia et al. NIM A 523(2004)334 1 Ion back-flow ratio H V GEM 3 V GEM 1 =350 V 315 V VGEM 2 =VGEM 3 280 V E =1. 0 k. V/cm T 1 E =E =0. 25 k. V/cm T 2 T 3 0. 1 250 V 2 -3% Eind =- 5. 0 k. V/cm High gain and low ion back flow: 2 -3% 350 V Ar/5%CH p=760 Torr 4 0. 01 1 E+02 RICH 04 Mexico Vhole 300 V 1 E+03 1 E+04 1 E+05 Effective Gain 1 E+06 A. Breskin

Ion back-flow reduction: reversed-MHSP & GEM J. Veloso et al. WIS/Coimbra IEEE 2004 MHSP: gain & ion blocking R-MHSP: ion defocusing* * R-MHSP: Roth, Vienna 04 R-MHSP C A Gain=30 ~300 ions/e 30 x gain 4 x ions! ~1200 ions/e MHSP AC WIS/Coimbra 10 -3 R-MHSP C A + IBF: Ion Backflow Reduction RICH 04 Mexico IBF R&D IN PROGRESS! A. Breskin

Other ion-suppression ideas Gain of 1 st element: 20 -30 RICH 04 Mexico A. Breskin

Ion backflow (reflective photocathode) Gain of R-MHSP 1 ~ 30 RICH 04 Mexico A. Breskin

Ion Gating E 1 E 2 1. Gate open => electron transfer 2. Gate closed, after electron transfer, => ions are stopped Non-gated GEM: at best 10% ion-feedback Gated GEM: ion suppression to 10 -4 levels! Problem: dead time! (ms) RICH 04 Mexico D. Mörmann et al. NIM A 516 (2004) 315 Feedback pulses 10 -4 A. Breskin

Gated GPMT for visible light GAIN: 100 -1000 in DC mode (ion feedback limit) >105 in ion-gating mode A breakthrough! >105 D. Mörmann et al. WIS 2004 RICH 04 Mexico A. Breskin

Ion-suppression: summary At gain ~ 105 • Multi-GEM: IBF = • 10 -1 – 2 10 -1 Multi-GEM & MHSP: IBF = 2 • 10 -2 Photocathode life-time, TPC , depends on the total ion’s accumulated charge on the photocathode: Multi-GEM & MHSP(MWPC GPM) x 1/IBF = 1 - • TPC (GEM-like GPM) = TPC & R-MHSP: Operate 3 10 -3 at minimal possible gain! Gated multi-GEMs: IBF = • RICH 04 Mexico A. Breskin -4

K-Sb-Cs photocathode ageing Aging of K-Cs-Sb under avalanche-ion bombardment in Ar-CH 4(5%) Cs. I KCs. Sb 4 -GEM / semitransparent photocathode a small fraction of ions hit the pc slow aging Cs. Br parallel-grids / semitrans. photocathode all ions hit the pc faster aging! RICH 04 Mexico A. Breskin

Summary • GEM photomultipliers (GPM): - a mature concept in the UV - important progress in the visible • Other advanced “hole-multipliers”: MHSP, TGEM (talk by Rachel Chechik) • Ion blocking: cascaded GEM/MHSP/RMHSP – 10 -3 importat also for TPCs! RICH 04 Mexico A. Breskin

FIN RICH 04 Mexico A. Breskin

LXe-gaseous PMT gamma-camera for PET HV 20 k. V Xenon gas GPM Cathode wire plane Thermal Screen 9 cm LXe PTFE Wall Metallic Micromesh Liquid Xenon HV [1 -2] k. V Anode plane 511 ke. V Gamma ray Si. O 2 entrance window (3 mm) SUBATECH-Nantes/WEIZMANN RICH 04 Mexico A. Breskin

Suggested GEM in the XENON Detector The XENON Dark Matter search: E. Aprile et al. Columbia Univ. astro-ph/0207670 1 ton liquid Xe detector with multi-GEM GAS PHOTOMULTIPLIER Xe GAS Replace LIQUID Xe Primary scintillation: Photo-effect in LIQUID & GAS Secondary scintillation: Induced by electrons extracted from LIQUID & drifting in GAS WIMPS RICH 04 Mexico A. Breskin

Suggested PHENIX HBD e- Simulation Real life…. HBD A single 100 Me. V electron identified by a “Cerenkov signal” in the HBD A single event recorded in the STAR TPC showing hundreds of particles: most of them HADRONS GEM-photodetector insensitive to particles! RICH 04 Mexico A. Breskin

TPC/HBD for RHIC-PHENIX I. Tserruya et al, WIS Large area UV detector 3 -GEM/Cs. I TPC Readout Plane Drift regions HV plane (~ -30 k. V) Readout Pads Grid DR ~ 1 cm f ~ 2 mm GOAL: identification of a few low-mass e-pairs out of hundreds of Hadrons / collision RICH 04 Mexico A. Breskin

Ion feedback to the ST photocathode GPM TPC Ion feedback as a function of the drift field 1% “standard” GEMs Breskin et al. NIM A 478(2002)225 Dependence on the gain: 3 GEM vs 4 GEM Bondar et al NIMA A 496(2003)325 Breskin et al. NIM A 478(2002)225 5% RICH 04 Mexico Factor 2 -3 IBF reduction A. Breskin

Ion back-flow in multi-GEM with reflective pc D. Mörmann et al. NIM A 516 (2004) 315 Variable: GEM voltage Variable: Induction field 20% 10% at best Variable: transfer field 20% RICH 04 Mexico A. Breskin