1. Spark probability measurement for GEM for CBM (Summary of the beam test at CERN SPS, October 2011)
Saikat Biswas, A. Abuhoza, U. Frankenfeld, C. Garabatos,
J. Hehner, T. Morhardt, C.J. Schmidt,
H.R. Schmidt, J. Wiechula
GSI Detector Laboratory
RD51 Mini week, June 2012, CERN

2. Outline of the talk Motivation Test set-up Analysis and Results
Summary and future plan

3. GEM for CBM
Triple GEM as a precise tracking detector in the Muon Chamber (MUCH) under the extreme conditions of the CBM experiment

4. Objective
To measure the properties of GEM with shower and in particular Spark probabilities of Double mask and Single mask GEM

5. Summary of beam test Detectors Measurement with Measured parameters
2 Double mask GEM
1 Single mask GEM
Measurement with
Pion beam
Pion beam with absorber: Shower
Measured parameters
Current
Voltage
Trigger and GEM Counts
GEM signal

6. Voltage distribution in GEM

7. Details of the set up Gas mixture: Ar/CO2: 70/30
7 channel HVG210 power supply
2 sum-up boards are used for signal (2×128 6×6 mm2 pads) for DM GEM
4 sum-up boards are used for signal (4×128 4×4 mm2 pads) for SM GEM
PXI LabView based DAQ is used

8. Set-up for Pion beam

9. Set-up for shower

10. Particle production during shower from FLUKA simulation
Ref. A. Senger

11. Comparison of shower number from measurement and simulation

12. Current

13. Current and GEM counting rate: Pion beam 300 kHz

14. Current and GEM counting rate during Shower: Beam rate300 kHz

15. Current as a function of rate for DM GEM
Pion beam
with absorber
Pion beam

16. Charge Vs. current for DM GEM
Slope: -1.38×10-12
Slope: -2.04×10-12
Pion beam
with absorber
Pion beam

17. Current as a function of rate for SM GEM
Pion beam
with absorber
Pion beam

18. Charge Vs. current for SM GEM
Slope: -1.35×10-12
Slope: -1.52×10-12
Pion beam
with absorber
Pion beam

19. Efficiency

20. Efficiency during shower

21. Efficiency as a function of rate during shower

22. Efficiency for pion beam

23. Efficiency vs. rate for pion beam

24. Spark probability measurement

25. Methods of Spark detection
Absence of signal
Drop in the counting rate of GEM signals
Data from sampling ADC
Detection of high current
Sudden increase in the Current (Slow)
Built in Trip checker in HVG210 Power supply (Fast)

26. No spark during a spill Double Mask GEM with Fe Absorber
Gas: Ar/CO2 : 70/30, Gas flow rate: 5 lt/hr, Particle rate: ~300 kHz, Pion beam
415_410_405

27. Drop in GEM counting rate
Double Mask GEM with Fe Absorber
Gas: Ar/CO2 : 70/30, Gas flow rate: 5 lt/hr, Particle rate: ~300 kHz, Pion beam
415_410_405

28. Sudden increase in current
Double Mask GEM with Fe Absorber
Gas: Ar/CO2 : 70/30, Gas flow rate: 5 lt/hr, Particle rate: ~300 kHz, Pion beam
415_410_405

29. Two sparks during a spill
Double Mask GEM with Fe Absorber
Gas: Ar/CO2 : 70/30, Gas flow rate: 5 lt/hr, Particle rate: ~300 kHz, Pion beam
415_410_405

30. Spark probability vs. global voltage for shower
Discharge probability:
No. of Discharge/ No. of incident particle

31. Spark probability vs. global voltage shower and pion beam

32. Spark probability vs. gain shower and pion beam

33. Spark probability vs. global voltage SM and DM

34. Off spill spark rate as a function of global voltage

35. Summary SPS test line has good conditions for our purpose
2 mm drift gap sub-optimal (3 mm standard!)
Efficiency
Rate dependency of efficiency observed
Pion (signal close to threshold!)
Shower (signal below threshold! Pick-up noise)
Spark probability
Spark measurement reliable also with noise (high thresholds)
Comparable spark probability for pion beam and shower (high rate) !
Higher spark probabilities for lower intensities (shower)
SM GEM
Was in conditioning phase.
No indication for different performance

36. Future plan: test beam Optimized drift gap (3 mm)
Conditioned counters (SM and DM)
Pixel readout ?

37. Acknowledgement
Thanks to the RD51 collaboration for their support in the beam test…. Thank you for your kind attention !

38. Back up slides

39. Conclusion The spark probability for pion beam is high.
May be the gain is not measured correctly!!
Effect of space charge !!
Investigated in different conditions.
to be understood the different spark probabilities.

40. Pulse height distribution

41. Method
100 sample is taken
Difference of the maximum and minimum value of the channel is taken as pulse height

42. Fe V
Resolution ~17.6%

43. For DM GEM at 400-395-390 with pion beam: Rate 300 kHz

44. For DM GEM at 415-410-405 during shower: Beam rate: 300 kHz

45. For SM GEM at 400-395-390 with pion beam: Rate 300 kHz

46. For SM GEM at 405-400-395 during shower: Beam rate: 300 kHz

47. Geometry of the experimental set-up

48. For SM GEM at 400-395-390 with pion beam: Rate 300 kHz

49. Definitions Spill: > 0.5 < 0.2 Spark: Spill Rbeam <R*beam>
CGEM
Cbeam
<RGEM>
<Rbeam>
< 0.2
Spill

50. Gain as a function of global voltage for SM GEM

51. Corrected voltage for GEM3

52. Discharge probability as a function of gain
No. of Discharge/ No. of incident particle
Ref: S. Bachmann et al., NIM A 470 (2001) 548–561

53. Spark rate as a function of global voltage