68 / 2024-07-12 14:45:15

Status of HV stability of CMS GEM detectors during LHC operations

Discharges,GEM,short,short circuits,operations

The upgrade program of the Compact Muon Solenoid (CMS) for the High Luminosity phase of the Large Hadron Collider (LHC) includes the installation of three GEM stations: GE1/1, GE2/1, and ME0. GE1/1 has been fully operational and contributing to data collection since the beginning of Run-3, while only a few GE2/1 modules have been installed as of the beginning of 2024. The installation of ME0 is scheduled during the LHC Long Shutdown 3 period. This contribution will primarily focus on the operation of the GE1/1 station in the presence of the LHC beam, particularly examining the stability of the detectors from the perspective of high voltage (HV). This stability is influenced by the HV baseline current (affected by background radiation) and the discharge rate. The study will illustrate how the HV baseline current varies with LHC beam luminosity and, consequently, with the background hit rate. Furthermore, this research can serve as a reference for estimating background levels for the upcoming installation of the next two GEM stations in CMS over the next few years, particularly for ME0. A second factor that can affect the operation of the detector is the generation of short circuits in the GEM foils. This contribution will illustrate the context of generation and healing of short circuits in GEM foil, providing suggestions for a safe operation of the detectors. Finally, the generation of discharges is observed in presence of LHC beam collisions, due to the background radiation. The contribution will provide an update on the observed discharge rate during the operation of the past year.