1. C.Shalem et al, IEEE 2004, Rome, October 18 R. Chechik et al. ________________RICH2004_____________ Playa del Carmen, Mexico 1 Thick GEM-like multipliers: a simple solution for large area UV-RICH detectors R. Chechik, A. Breskin and C. Shalem Dept. of Particle Physics, The Weizmann Institute of Science, 76100 Rehovot, Israel

2. C.Shalem et al, IEEE 2004, Rome, October 18 R. Chechik et al. ________________RICH2004_____________ Playa del Carmen, Mexico 2 30 years of “Hole-multiplication” history: Breskin, Charpak NIM108(1973)427 discharge in glass capillaries Lum et al. IEEE NS27(1980)157, Del Guerra et al. NIMA257(1987)609 Avalanches in holes Bartol, Lemonnier et al. J.Phys.III France 6(1996)337 CAT Sakurai et al. NIMA374(1996)341, Peskov et al. NIMA433(1999)492 Glass Capillary Plates GEM Sauli NIMA386(1997)531 GEM Ostling, Peskov et al, IEEE NS50(2003)809 G-10 “Capillary plates ”

3. C.Shalem et al, IEEE 2004, Rome, October 18 R. Chechik et al. ________________RICH2004_____________ Playa del Carmen, Mexico 3 Expanding the standard GEM… 1-2 holes/mm 2 PCB tech. of etching + drilling Simple and robust  Sub-mm to mm spatial resolution V TGEM ~2KV (at atm. pressure) 10 5 10 5 gain in single-TGEM, 10 7  10 7 gain in double-TGEM   Fast (few ns)  (<1 Torr10 4  Low pressure (<1 Torr) gain 10 4  50 holes/mm 2 Microlithography + etching High Spatial resolution (tens of microns) V GEM ~400V >10 3 >10 3 gain in single GEM 10 6 10 6 gain in cascaded GEMs Fast (ns) Low pressure – gain~30 1mm TGEM Standard GEM Geometry: similar to “Optimized GEM” [Peskov] But: etched rim

4. C.Shalem et al, IEEE 2004, Rome, October 18 R. Chechik et al. ________________RICH2004_____________ Playa del Carmen, Mexico 4 Expanding the standard GEM ? What scales up? The GEM geometry and what does not? Electric fields Electron diffusion Electron transport Gain Timing properties Rate capability Ions transport -> it is a new device that has to be studied from scratch !

5. C.Shalem et al, IEEE 2004, Rome, October 18 R. Chechik et al. ________________RICH2004_____________ Playa del Carmen, Mexico 5 The TGEMs: A TGEM costs ~4$ /unit. With minimum order of 400$  ~120 TGEMs. >10 times cheaper than standard GEM from CERN.

6. C.Shalem et al, IEEE 2004, Rome, October 18 R. Chechik et al. ________________RICH2004_____________ Playa del Carmen, Mexico 6 Various TGEMs studied at WIS drilling Cu etching Manufactured by standard PCB techniques of precise drilling in G-10 (+ other materials) and Cu etching. Typical Atm.pressure geometry Low pressure geometry Hole diameter d=0.3mm Distance between holes a =0.7mm Thickness t =0.4mm Hole diameter d=1mm Distance between holes a =1.5mm Thickness t =1.6mm 0.1mm rim to prevent discharges Important for high gains! 0.1mm Cu G-10 3cm

7. C.Shalem et al, IEEE 2004, Rome, October 18 R. Chechik et al. ________________RICH2004_____________ Playa del Carmen, Mexico 7 Electric field & e - transport calculations: Maxwell / Garfield E~4 (KV/cm) E~25 (KV/cm) Operated at V TGEM ~2KV Field values on electrode surfaces Field value inside the holes Field direction->focusing into the holes Dependence on the hole parameters  multiplication Hole length

8. C.Shalem et al, IEEE 2004, Rome, October 18 R. Chechik et al. ________________RICH2004_____________ Playa del Carmen, Mexico 8 Operation principle E drift E TGEM E trans Garfield simulation of electron multiplication in Ar/CO 2 (70:30) Multiplication inside holes -> reduces secondary effects Each hole acts as an individual multiplier

9. C.Shalem et al, IEEE 2004, Rome, October 18 R. Chechik et al. ________________RICH2004_____________ Playa del Carmen, Mexico 9 TGEM as a Photon detector Considerations: 1.High field on the pc surface, to minimize back scattering. 2. Good e - focusing into the holes, to maximize effective QE. 3.Low sensitivity for ionizing background radiation. Solution: a reflective pc on top of the TGEM. Slightly reversed E drift (~50V/cm) good photoelectron collection! Low sensitivity to MIPS

10. C.Shalem et al, IEEE 2004, Rome, October 18 R. Chechik et al. ________________RICH2004_____________ Playa del Carmen, Mexico 10 For typical operation voltages: Surface field > 5kV/cm  Full photoelectron extraction High effective QE TGEM as a Photon detector (‘cont) TGEMs studied so far are more optically transparent than standard GEM. Cu: 40-50% area 0.4mm thick 0.3mm holes 0.7mm pitch

11. C.Shalem et al, IEEE 2004, Rome, October 18 R. Chechik et al. ________________RICH2004_____________ Playa del Carmen, Mexico 11 Effective gain and effective QE effective gain:  measured gain in current mode is an effective gain: Effective gain = true gain in X efficiency to focus the holes the e - into the holes. effective QE  QE in the detector is an effective QE: Eff. QE = true QE X efficiency to X efficiency to of the pc extract the ph.e. detect the ph.e. i PC GEM Reflective pc i PC GEM Semitransparent pc

12. C.Shalem et al, IEEE 2004, Rome, October 18 R. Chechik et al. ________________RICH2004_____________ Playa del Carmen, Mexico 12 Gain 10 4 -10 5 Single-photon detection no photon feedback Rise time < 10ns 10ns Example: TGEM with reflective CsI photocathode (Similar results with semitransparent pc) Single-TGEM: Gain 10 5

13. C.Shalem et al, IEEE 2004, Rome, October 18 R. Chechik et al. ________________RICH2004_____________ Playa del Carmen, Mexico 13 Higher total gain (10 6 -10 7 ) >10 3 higher gain at same V TGEM Better stability Double-TGEM: Gain 5 mm E trans = 3kv/cm e-e- Important for double TGEM: high E trans Large transfer gap 10 7 Example: TGEM with a semitransparent CsI photocathode (similar results with reflective pc)

14. C.Shalem et al, IEEE 2004, Rome, October 18 R. Chechik et al. ________________RICH2004_____________ Playa del Carmen, Mexico 14 Problem: Requires high TGEM voltage. Damage due to sparks is fatal: after a spark the TGEM deteriorates continuously. (We suspect effects of etching to the SiO 2 fibers). Fatal spark damage was also observed in standard GEMs operating in CF 4, due to the high operating voltages. Solutions: Segment the TGEM Cascade several TGEMs. Test other materials: Kevlar, Teflon, etc. Operation in CF 4 R. Chechik et al. ________________RICH2004_____________ Playa del Carmen, Mexico

15. C.Shalem et al, IEEE 2004, Rome, October 18 R. Chechik et al. ________________RICH2004_____________ Playa del Carmen, Mexico 15 Electron transfer efficiency  Electron transfer efficiency  TGEM with a reflective pc (E drift =0)  e affects energy resolution, detection efficiency, effective QE Compared to standard GEM, very high fields are reached at the TGEM surface already at low V TGEM. Good e - extraction in all gases. FfFf Transfer efficiency 0.4mm thick 0.3mm holes 0.7mm pitch

16. C.Shalem et al, IEEE 2004, Rome, October 18 R. Chechik et al. ________________RICH2004_____________ Playa del Carmen, Mexico 16 Electron transfer efficiency  Electron transfer efficiency  TGEM with a semitransparent pc   is important also for double TGEM operation (more complex measurement) Double-sided pc Double normalization Single e - pulse counting as before Full efficiency already at low gains gains 10-100 ! 0.4mm thick 0.3mm holes 0.7mm pitch

17. C.Shalem et al, IEEE 2004, Rome, October 18 R. Chechik et al. ________________RICH2004_____________ Playa del Carmen, Mexico 17 Electron transfer efficiency  -cont’ Electron transfer efficiency  -cont’ TGEM with a semitransparent pc - dependence on E drift /V TGEM E TGEM /E drfit > 1 e - focused to hole E TGEM /E drfit < 1 e - collected on GEM top With typical TGEM operation voltage: full eff. up to E drift = 4kv/cm 0.4mm thick 0.3mm holes 0.7mm pitch

18. C.Shalem et al, IEEE 2004, Rome, October 18 R. Chechik et al. ________________RICH2004_____________ Playa del Carmen, Mexico 18 Energy resolution: 6 keV x-rays FWHM=~20% E resolution similar to standard GEM 6 keV x-rays

19. C.Shalem et al, IEEE 2004, Rome, October 18 R. Chechik et al. ________________RICH2004_____________ Playa del Carmen, Mexico 19 Counting rate capability  Reflective CsI pc  UV photons (185nm) Total current limit 4*10 -7 [Amp/mm 2 ] 0.4mm thick 0.3mm holes 0.7mm pitch

20. C.Shalem et al, IEEE 2004, Rome, October 18 R. Chechik et al. ________________RICH2004_____________ Playa del Carmen, Mexico 20 Ion back flow Ion back flow  Affects pc longevity and secondary effects TGEM with a semitransparent pc s.t. pc Start amplification IBF = i pc /i TGEM 12% With high V TGEM most of the ions are collected on the top of the TGEM. 0.4mm thick 0.3mm holes 0.7mm pitch

21. C.Shalem et al, IEEE 2004, Rome, October 18 R. Chechik et al. ________________RICH2004_____________ Playa del Carmen, Mexico 21 Ion back flow Affects pc longevity and secondary effects TGEM with a reflective pc Reflective pc IBF = i pc /i TGEM With a reflective photocathode, most of the ions are collected on the top of the TGEM (like in a GEM).

22. C.Shalem et al, IEEE 2004, Rome, October 18 R. Chechik et al. ________________RICH2004_____________ Playa del Carmen, Mexico 22 Summary 1.G-10 TGEMs tested with several gases. 2.Gains: 10 5 with a single TGEM; 10 7 with cascaded double TGEM 3.Fast signals: r.t. <10 ns. 4.The e - transfer efficiency (into the holes) is well understood. 5.Counting rate capability: ~ 10 6 avalnches/sec x mm 2 @ gain 4x10 4 6.Ion backflow: study in course 7.In TPC-like conditions: IBF with a single TGEM is 12%. In GPM/reflective pc: IBF with a single TGEM is 98%. A cascade + other “tricks” (see GEM/MHSP) should reduce IBF. 8. TGEMs of different materials (e.g. Kevlar, Teflon…) for CF 4 ?. 9. Will study TGEM of lower optical transparency (higher eff. QE)

23. C.Shalem et al, IEEE 2004, Rome, October 18 R. Chechik et al. ________________RICH2004_____________ Playa del Carmen, Mexico 23 The end

24. C.Shalem et al, IEEE 2004, Rome, October 18 R. Chechik et al. ________________RICH2004_____________ Playa del Carmen, Mexico 24 TGEM: Low pressure operation Single TGEM 10 Torr Isobutane Gain~10 5 ; Rise time~5ns  low pressure isobutane  semi-transparent CsI photocathode

25. C.Shalem et al, IEEE 2004, Rome, October 18 R. Chechik et al. ________________RICH2004_____________ Playa del Carmen, Mexico 25 TGEM: Low pressure operation  low pressure isobutane  semi-transparent CsI photocathode

26. C.Shalem et al, IEEE 2004, Rome, October 18 R. Chechik et al. ________________RICH2004_____________ Playa del Carmen, Mexico 26 Electron transfer efficiency Electron transfer efficiency the efficiency to focus an electron into the TGEM Pulse counting measurement: A way to separate the true gain from the effective gain. Based on single e - pulses same pc, lamp, gain and electronics, different e - path. Comparing counting rate provides the fraction of single e events reaching TGEM bottom. (1) normalization (2) efficiency measurment Example: ref pc