1. Update on THGEM project for RICH application Elena Rocco University of Eastern Piedmont & INFN Torino On behalf of an Alessandria-CERN-Freiburg-Liberec- Prague-Torino-Trieste Collaboration

2. Outline Short introduction; In order to detect the single photon, we investigated many aspects: Multilayer detector; Spectra and gains; Time resolution; Photoelectron extraction efficiency. Conclusions CERN, 29 April 20092Elena Rocco - RD51 week

3. Short Introduction (1/2): From the systematic characterisation studies over 30 THGEMs we learned the following: 1. Use the smaller rim possible (i.e. 10 μ m) for limiting the gain instabilities vs time; 2. Maximum gain variation of 20% over a range of several MHz/mm 2 ; 3. The production aspect is not negligible and to fix as important geometrical parameter as well. CERN, 29 April 20093Elena Rocco - RD51 week

4. Short Introduction (2/2): Up to now we tested the THGEMs as detector for ionizing particle and now we are verifying the THGEMs as photon detector. CERN, 29 April 2009Elena Rocco - RD51 week4

5. Multilayer detector for single photon detection 30 mm CsI coating no coating anode (with pads ) drift WIRES THGEM 2 E induction E transfer 2.0 mm CsI THGEM 3 THGEM 4 2.0 mm THGEM 1 THGEM geometry: - thickness = 0.4 mm - hole diameter = 0.4 mm - pitch = 0.8 mm -rim = 10 μm NOTE: reflective photocathode CERN, 29 April 20095Elena Rocco - RD51 week

6. UV light Pulse Source 1. Model UV LED-255 by Seoul Optodevice Co., Ltd, Seoul, Korea (South) Central wavelength: 255 ± 10 nm Spectral line width: <20nm FWHM ◦also called germicidal ray (disinfection) ◦Applications: Water/Surface purification, Laboratory testing 2. PLS 265-10 (pulsed LED) and controller by PicoQuant GmbH, Berlin, Germany 600 ps long pulses up to 40 MHz UV LED-255 peak @ 258 PLS 265-10 peak @ 269 spectrophotometer measurement 220 240 260 280 300 nm CERN, 29 April 20096Elena Rocco - RD51 week

7. Single photon detection: amplitude spectra ─ gain: 110 000 ─ gain: 113 000 stable detector behaviour at gains up to ~130 000 Ar/CH 4 : 50/50 CERN, 29 April 20097Elena Rocco - RD51 week

8. Single photon detection: time resolution Recall: TDC bin size: 108 ps pulse width: 600 ps No detector optimisation for time response performed so far CERN, 29 April 20098Elena Rocco - RD51 week

9. Photoelectron extraction (1/6) fused silica window e-e- pA CsI UV light source Keithley picoAmp atmospheric pressure, reproducibility @ 1% level E(V / cm) photocurrent (pA) ─ CH 4 ─ Ar/CH 4, 66/34 ─ Ne/CH 4, 62/38 ─ Ar/CO 2, 70/30 10 mm Photocurrent measurements in various gas atmospheres CERN, 29 April 20099Elena Rocco - RD51 week

10. Photoelectron extraction (2/6) Photoelectron extraction vs V and E, simulations and measurements anode (with pads) WIRES (V1) CsI THGEM 1 ( top: V2, bottom: V3) E fused silica window E = (V2-V1) / d V = V3 – V2 d UV Light source E field, sign convention 0 CERN, 29 April 200910Elena Rocco - RD51 week

11. Photoelectron extraction (3/6) photoelectron trajectories from a THGEM photocathode, simulation, multiplication switched off thickness 0.6 mm, diam. 0.4 mm, pitch: 0.8 mm, ΔV = 1500 V x cross-section y cross-section external field above the THGEM : 0 x y CERN, 29 April 200911Elena Rocco - RD51 week

12. Photoelectron extraction (4/6) photoelectron trajectories from a THGEM photocathode, simulation, multiplication switched off thickness 0.6 mm, diam. 0.4 mm, pitch: 0.8 mm, ΔV = 1500 V external field above the THGEM : - 500 V /cm: photoelectron lost (not entering the holes) E x cross-section y cross-section x y CERN, 29 April 200912Elena Rocco - RD51 week

13. Photoelectron extraction (5/6) photoelectron trajectories from a THGEM photocathode, simulation, multiplication switched off thickness 0.6 mm, diam. 0.4 mm, pitch: 0.8 mm, ΔV = 1500 V E x cross-section y cross-section x y x y external field above the THGEM : + 500 V /cm: photoelectron lost (too low field to extract them) CERN, 29 April 200913Elena Rocco - RD51 week

14. Photoelectron extraction (6/6) Anodic current in a THGEM detector versus the external electric field applied, a measurement Ar/CH 4 : 40/60; 60/40 V = 1kV 1.1, 1.2 1.25, 1.3 1.35 1.5 The behaviour predicted by the simulation is confirmed!  A clear suggestion to optimise the detector design ZOOM CERN, 29 April 200914Elena Rocco - RD51 week

15. Conclusions Intense R&D activity towards THGEM based photon detectors ◦In parallel and in close contact with Weizmann, Coimbra, Bari, ST.Etienne in the context of RD51 – the MPGD R&D Collaboration. Detection of single photons: ◦Gains > 10 5 in electrically stable detectors with ≤10 m rim and a 4-layer structure; ◦time resolution ~ 7 ns; ◦effective photoelectron extraction possible in CH 4 mixtures. NO STOPPING POINTS DETECTED, even if still a long way to go… CERN, 29 April 200915Elena Rocco - RD51 week