Recent THGEM investigations A. Breskin, V. Peskov, J. Miyamoto, M. Cortesi, S. Cohen, R. Chechik Weizmann Institute RD51 Paris Oct 08 - Gain: UV vs. X-rays - Gain stability - What’s next? THGEM Recent review w refs: BRESKIN et al THGEM cooperation also with: Coimbra, PTB, Soreq NRC, Milano univ, UTA…

Among current applications: Gy/h mm photons LXe Medical: LXe Gamma camera Pos-sens n-dosimetry - BNCT N-detectors n elemental radiography Gas photomultipliers 2-phase LXe detectors for rare events Also: Calorimetry

THGEM 0.5mm holes holes drilled in thick G-10 Thick Gas Electron Multiplier (THGEM) SIMPLE, ROBUST, LARGE-AREA  Intensive R&D  Many applications 1 e - in e - s out E THGEM Double-THGEM: higher gains Robust Single-photon sensitivity Effective single-photon detection 8ns RMS time resolution Sub-mm position resolution >MHz/mm2 rate capability Cryogenic operation: OK

Gain: UV vs X-rays To clarify: “are WIS previous results of “higher gain with UV compared to x-rays” - OK? Method: compare both UV and x-rays with the same detector in a single experiment

Single- & double-THGEM with UV (recall) Shalem et al NIM A558(2006) mm thick 0.4mm thick - Gain 2-THGEM / 1-THGEM ~100 - Gain 2-THGEM: function of E trans - 2-THGEM: lower V hole - 1-THGEM: low thickness-effect on gain: gain0.8mm/gain0.4mm ~2

Cortesi et al 2007 JINST 2 P09002 Double-THGEM with 6 keV x-rays (recall) 10 4

pA -Vdr Hg lamp TGEM Window -Vtop 55Fe Am (for gain calibration) pA UV light 2cm Mesh New measurements: Experimental set up To pump Gas in Gas out CsI THGEM geometry: Holes dia: 0.5 mm Pitch: 1 mm Thickness: 0.8 mm Rim: 0.1mm

Maximal gains with UV are 100 times higher than with X-rays. For UV and x-ray gun: The current in the plateau region ( V) was the same: 0.1nA. The maximum current in gain measurements was always kept below 0.5nA 55 Fe NEW Pulse-mode (~1kHz) Cu X-ray gun, current-mode Single-THGEM : Ar+5%CH 4 WIS old pulse-mode UV Current-mode NEW 10 4 THGEM geometry: Holes dia: 0.5 mm Pitch: 1 mm Thickness: 0.8 mm Rim: 0.1mm

Single-THGEM: Ne UV, current-mode 55 Fe Pulse-mode The maximum gains with x-rays in Ne are higher than in Ar+5%CH 4. In Ne breakdown voltages with UV and X-rays are closer THGEM geometry: Holes dia: 0.5 mm Pitch: 1 mm Thickness: 0.8 mm Rim: 0.1mm 10 4

Single-THGEM: Ne + CH 4 Same as with Ne: maximum gains with x-rays in Ne+CH 4 are higher than in Ar+5%CH 4 and breakdown voltages with UV and X-rays are close. 55Fe Pulse-mode 55Fe Pulse-mode UV Current-mode UV Current-mode THGEM geometry: Holes dia: 0.5 mm Pitch: 1 mm Thickness: 0.8 mm Rim: 0.1mm 10 4

A possible interpretation (Peskov) - Raether limit: established in large-gap avalanche detectors but valid for MPGDs (Ivanchenkov NIM A 1999), though may be different - A*n 0 = electrons where A is the maximum achievable gain, n0-number of primary electrons deposited by the radiation in the drift region  X-rays: different gain compared to UV - In Ne/CH 4 Raether limit possibly differs from Ar/CH 4 due to ~ 5-fold longer range of 55 Fe photoelectrons (~1mm), resulting in lower ioinization density per “hole”. To verify with alphas, hadronic beams etc

GAIN STABILITY

THGEM Long-term stability: recall Insulator Charging up  Hole&rim:few hours of stabilization (gain variation ~ factor 2.) Stabilization time function of: Total gain (potentials) Counting rate (current) Material & hole-geometry (dia., rim) Production method Gas & purity (e.g. moisture) i ST PC 1mm R. Chechik SNIC2006, Gain Ar/5%CH4 UV, 5x10 5 e-/mm

Stability with UV: new data Single-THGEM geometry: Holes dia: 0.5 mm Pitch: 1 mm Thickness: 0.8 mm Rim: 0.1mm Charge-up: gain dependent Ar/5%CH 4 – flow mode

THGEM GAIN STABILITY – X-RAYS Fe-55 source collimated by a 3 mm dia hole Anode Mesh 2nd THGEM 1 st THGEM Drift mesh 9.6 mm1.6 mm Vary the distance To change the rate THGEM geometry Material FR-4 Thickness 0.4 mm Hole size 0.6 mm Pitch 1.0 mm Rim size 0.1 mm E_drift = 100 V/cm E_transfer 1 kV/cm E_inducion= 4 kV/cm

SETUP Collimated X-rays Pure argon gas in Gas out ThGEM Heated Baraton Gauge for pressure monitoring (4Torr change in 24h) Charge Amp+Shaper+MCA for pulse height analysis RGA 200 gas analyzer for purity check Temperature sensor placed on the chamber surface (0.8C in 48h) Hamamatsu PMT for photon counting Anode signal UHV vessel Gas can: - Flow - Circulate via getter Gain corrected for pressure-changes; T-changes negligible

For a very short-term scales (<1 hr), the drop in gain is faster for higher rates The magnitude of drop function of rate Argon, 770 Torr GAIN VARIATION vs RATE I 7Hz/mm 2 30Hz/mm 2 120Hz/mm 2 300Hz/mm 2 X-RAYS Gain 2000

Stability reached after ~ 5h for gains ~1400 for 7-300Hz/mm 2 Data normalized to pressure=770 Torr GAIN VARIATION vs RATE II X-RAYS Argon, 770 Torr Gain Hz/mm 2 300Hz/mm 2

1.At higher rate, after initial drop, the gain keeps rising while at lower rate the gain stabilizes at low value. 2. At higher rate the detector occasionally discharges, whereas at lower rate the detector is rather stable 3. Gain recovery after a discharge is faster at higher rates. Sparks followed by quick recovery (high rate) Spark followed by slow recovery (low rate) At high rate continuous sparks begin when the gain recovered sufficiently Gain 10,000 GAIN VARIATION vs RATE – higher gain vs rate

Lower gain: rates 7 Hz/mm 2 & 70 Hz/mm2 1. At higher rate, the initial drop is shaper 2. At higher rate, after the sharp drop the gain tends to reach faster the stability observed for the lower rate. 3. The stabilization time is longer for low gain & higher rates. Gain 500 GAIN VARIATION vs RATE – lower gain vs rate

Summary of charge up in pure Ar 1.At low rates: gain drops to a certain level and remains constant regardless of initial gain (500-10,000) 2. At higher rates: gain sharply drops to its minimum. The magnitude of the drop is the largest at high gain. After reaching minimum, the gain tends to recover to the value reached at low-rates. The recovery is faster at the higher gains. 3. At high rate and high gain the gain recovery did not reach stable level – discharges due probably Raether limit in Ar.

Fulvio TESSAROTTO GDD meeting, CERN, 01/10/2008 Trieste THGEM news RIM: 0.1 mm RIM: 0 Long time GAIN variation Short time GAIN variation RIM: 0 RIM: 0.1 mm Single THGEM, th. 0.4, Ø 0.4, p. 0.8 irradiation at HV switch on (after ~1 day with no voltage) irradiation after ~10 hour at nominal voltage without irradiation TRIESTE Results GAIN STABILITY: rim/no-rim TRIESTE RESULTS Remark: Comparison at diff gains

Fulvio TESSAROTTO GDD meeting, CERN, 01/10/2008 Trieste THGEM news Gain variation studies in different conditions TRIESTE results For first series of “Eltos” pieces (with th. 0.4, diam. 0.4, pitch 0.8), Ar/CO 2 70/30 and 55 Fe source (~ 600 Hz), in Trieste, first 12 h: 100 μm chem. rim  increase of ~ 400% 50 μm mech. rim  still to be processed: large decrease 25 μm chem. rim  decrease of ~ 70% 10 μm chem. rim  decrease of ~ 50% (“global etching”) no rim  decrease of < 30% The time to reach stabilization is shorter for smaller rims CsI deposited on pieces with 100 μm rim and with no rim: gain variations with photons ~ similar to those seen with X rays ?  

THGEM Segmented Anode MgF2 window LXe conversion volume THGEM-GPM for LXe Gamma Camera CsI photocathode Subatech-Nantes/Weizmann IN CONSTRUCTION LXe/GPM Tests: Jan 09

300x300mm2 THGEM!

300x300 THGEM THGEM geometry: Hole dia.: 0.5 mm Pitch: 1 mm Thickness: 0.4 mm (Cu~ 35 mic) Rim: 0.05 mm (can be smaller) Chemical etching/no mask Ni/Au plating Producer: Print Electronics

SUMMARY ● In Ar+5%CH 4 the maximum achievable gains measured with UV-light (~10 6 ) are ~100-fold higher than with 55 Fe (~10 4 ) ● Probable explanation is the Raether limit ● In Ne and Ne-CH 4 (5-23%) mixtures, under gas flushing, the maximum gains with UV and 55 Fe are closer ( ) ● Possible explanation: 55 Fe photoelectron-tracks are longer in Ne and its mixtures  lower density of ionization per hole  lower max. gain-difference caused by charge-density effects. ● In pure Ne  scintillation prevents high gains & “masks” p.e. extraction  quencher ● For RICH: optimal would be Ne–based mixtures ● Quencher additives to be optimized – for high gain and efficient p.e. extraction. ● Preliminary results indicate upon ~70% extraction efficiency in Ne/23%CH 4  similar to Ar/5%CH 4. ● Charge-up: geometry (rim), gain and rate dependent. ● It seems that rimless holes are advantageous, but need to establish detectors’ parameters (eff QE, e-transfer photon detection efficiency) with the right conditions and gas ● Need to compare stability of LARGE-AREA rim/rimless THGEMs with UV photons ● Tests in RICH mode? Who? When? – Trieste ordered 60x60 cm THGEMs. ● 30x30cm THGEM tests: tested end 2008 at WIS ● Expected results in Cryo-THGEMs Gas Photomultipliers/LXe: early 2009.