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, 13-15 June 2012, CERN

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

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

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

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

Voltage distribution in GEM

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

Set-up for Pion beam

Set-up for shower

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

Comparison of shower number from measurement and simulation

Current

Current and GEM counting rate: Pion beam 300 kHz

Current and GEM counting rate during Shower: Beam rate300 kHz

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

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

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

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

Efficiency

Efficiency during shower

Efficiency as a function of rate during shower

Efficiency for pion beam

Efficiency vs. rate for pion beam

Spark probability measurement

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)

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

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

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

Two sparks during a spill 412 - 407 - 402 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

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

Spark probability vs. global voltage shower and pion beam

Spark probability vs. gain shower and pion beam

Spark probability vs. global voltage SM and DM

Off spill spark rate as a function of global voltage

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

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

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

Back up slides

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.

Pulse height distribution

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

Fe55 spectrum @ 400-395-390 V Resolution ~17.6%

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

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

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

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

Geometry of the experimental set-up

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

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

Gain as a function of global voltage for SM GEM

Corrected voltage for GEM3

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

Spark rate as a function of global voltage