[Sbs_gems] [Revised Logentry] [GEM] INFN J0 Mid Problem

[ewertz at jlab.org]

Logentry Text:
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See Log entries:

https://logbooks.jlab.org/files/2021/12/3955238/summaryPlots_12496_bb_gem_for_shiftcrew.pdf  Page 24
https://logbooks.jlab.org/entry/3955234
https://logbooks.jlab.org/entry/3955221
https://logbooks.jlab.org/entry/3955220
https://logbooks.jlab.org/entry/3955216

At around 21:15 I was notified by the shift crew of a problem with J0 Mid. From these log entries it is clear that there was a problem with J0 mid around 18:50 today. The exact cause it still not known, but one can speculate that there was sparking, a GEM foil collapsed, or new shorted sectors were created. We shall communicate with other GEM experts and seem what is the likely candidate. What is evident is that with beam off before this time the current readback for the HV of J0 Mid was about 104.7 uAmps. After this occurred the current readback was about 111.3 uAmp. From the 50k replay it would seem that the efficiency of this module has become significantly reduced and effectively inoperable. GEM folks will need to evaluate this more and determine how to proceed. Unfortunately this may be an indicator that we are reaching some of the limitations of the hardware. Also unfortunately due to the trip limits of the HV it seems this detector did not trip off and continued to ap!
 ply HV to the GEM detector. J0 Middle is right in the middle of the acceptance for this detector so that's not good. But given the rates which the detectors are seeing, it makes some sense that the middle module would be most affected. Until further notice I have instructed the shift crew to keep J0 Middle off.


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