Meeting 2024 04 24

GMn GEM commissioning Meetings: WEDNESDAY 10:30am - 11:30am

Link to all previous meetings: GMn GEM Commissioning Meeting

Please use sbs_gems mailing list for plots/communications and HALOG entries relevant to GEMs!

Thursday night, as we moved to H at 25uA, several shorts occurred in SBS [1]
To our knowledge, the gas mix and the HV set points to the SBS GEMs are the same as always during running. They have new individual channel power supplies. [2]
The gain in the SBS GEMs appeared to be very high (so either mix is not what we think or HV too high or both).
Single sector shorted in BB when the gas mixture spiked to 90% on Friday due to empty CO2 and lack of alarms. Alarms and shutoff script are in place and verified now.
Gas flow to SBS is now set to 70/30 (what we think is 70/30), and HV is reduced and tweaked across G1 to improve the gain. [3][4]
Offline software thresholds reduced to 3sigma also shows improvement in efficiencies.
Work done yesterday to decouple (HV) two of the SBS chambers that were previously unable to run. [5]
Plan in the near future: install a small wire chamber on the SBS gas line to monitor gas, install a photon filter ~ 0.5" Aluminum plate on the SBS side to reduce occupancies.
Recent efficiencies in SBS: [6]
Lowered online zero suppression thresholds to 3sigma [7]

L3M3L2M1 (G2 &G3) — L3 faces the analyzer, L2 is high..decoupled now and only running L2M1 (L3M3 off)
L4M0M1 (G2) — faces the analyzer, high ...decoupled now and only running L4M1 (L4M0 off)
L5M2M3 (G2) - this one is low and possibly accessible, but needs to be slid out
L6M0M1 (G3) (beamline side) – it’s high and likely hard to reach
L6M2M3 (G3) — this one is low and possibly accessible, but probably too tight a fit to check anything
L8M0M1 (G2 & G3) – might be easily checkable from the platform with a stepladder or the one with handrails. This is on the HCAL side. (currently kept off)
L6M0 gas issue? - not a gas issue, probably one of the electrodes are disconnected from the HV distribution. This is most likely to have happened right at the detector. Another possible cause could be one of the gem foils being at reverse polarity.
L9M2M3 - Transfer 2 HV channel does not ramp up beyond certain values. see https://logbooks.jlab.org/entry/4289553

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