View source for GEM Fall Studies

== 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.
{| class="wikitable" style=text-align: center" cellspacing = "0" border = "1"
|-
! 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 [https://hallaweb.jlab.org/wiki/images/6/68/Fadc-cfd-fit.png full time range] and [https://hallaweb.jlab.org/wiki/images/c/c0/Fadc-cfd-fit-room.png 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.
*[https://hallaweb.jlab.org/wiki/images/b/b8/Timeresolution-hv3.56k-lvps3v.pdf Time resolution plot]. The 
*[https://hallaweb.jlab.org/wiki/images/6/62/HV%26Efficienc.pdf Efficiency plot ] for a cut of 50 ADC channels. Expect aaximum efficiency of 81.4% from trigger.