GEM Fall Studies

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Studies for GEM "pad" readout

  • Initial studies (Oct 28, 2011)
    • General Setup: 90Sr source with scintillator below the GEM as the trigger. Threshold on the scintillator is 40mV. The GEM is a "pad" readout with one preamp. The gas for GEM is Ar/CO2 at 75/25 mixture.
    • DAQ is using the flash ADC with GEM in Chan 1 and Scintillator in Chan 2. Flash ADC is sampling at 250Mhz so sample every 4nsec.
Run Number GEM HV Comment
1025 3.4kV Low voltage on preamp = 3.5V
1026 3.52 Scint signal was missing. Forgot to plug it back in after looking at scope.
1027 3.52 Event rate = 56/sec
1028 3.52 No source. Event rate = 10.4 /sec. So maximum GEM efficiency is 81.4%.
1029 3.52
1030 3.56
1031 3.47
1032 3.47 Low voltage on preamp = 5.0V
1033 3.53
  • Plots of flash ADC value versus the sample number for the full time range and smaller time range. The blue line is a fit with a Landau function. The red line is a "constant fraction discriminator" line which is basically trying to simulate a CFD by adding the inverse of the blue curve with a time offset and different scale. Needs to be optimized.
  • Time resolution plot using the sample number ( 4ns/sample). The time is determined by the zero crossing of the "CFD". The sigma is about 12ns.
  • Efficiency plot for a cut of 50 ADC channels. Expect a maximum efficiency of 81.4% from trigger. The 2d plots are the "CFD" zero crossing versus the height of the ADC for different run conditions. The lower right plot is the efficiency which is near the maximum.