Discharge rate and short circuits in GEM in 2022 and 2023

GE1/1 chambers in 2022 were affected by frequent protection turn off of the High Voltage power (HV trip) during the first LHC fills (8 colliding bunches). This was due to the occurrence of discharges inside of the detector. The main hypothesis is that the occurrence of discharges is favoured by the presence of imperfections in the manufacturing of holes of the GEM foils. In case of ionization by a Highly Ionising Particle (HIP), the charge density in the GEM hole during the multiplication avalanche can be high enough to overcome the Reather limit, triggering a discharge. The HIPs are produced during proton proton collisions. Indeed, discharges are mostly observed in presence of beam collisions. The d ischarge rate decreased over time due to the conditioning effect, produced by the irradiation of detectors. The final HV working point adopted in 2022 was 690 uA of equivalent divider current. In 2023, HVs were set at lower values at the very beginning, and GE1/1 chambers are currently operating at 680 uA and stable. We summarize (A) time evolution of short circuits in 2022 and (B) measurements of discharge rates.