Speaker
Description
Gas Electron Multiplier (GEM) has become a widely employed technology in modern particle and nuclear physics experiments. Despite great advancements in their construction and performance, the formation of electrical discharges remains one of the major factors limiting the long-term stable operation of GEM detectors and it is crucial to develop methods to mitigate them. In this work GEM and Thick GEM structures, incorporating conductive layers made of copper, aluminium, molybdenum, stainless steel, tungsten and tantalum, are studied. The focus of the study is to determine material dependence on the formation of electrical discharges in GEM-based detectors. For this task, in addition to the discharge probability measurements conducted using a basic electronics readout chain, also optical spectroscopy methods are employed to study the light emitted during discharges from the different foils. It is observed that the light spectra of GEMs include emission lines from the conductive layer material. This indicates the presence of the foil material in the discharge plasma after the initial spark. However, no lines associated with the coating material are observed with THGEMs. Furthermore, it was observed that the used conductive layer material does not substantially affect the stability against primary discharges. This agrees with the expectations from the streamer theory of primary discharge formation. However, strong material dependence is observed in the case of delayed secondary discharge formation. Especially, molybdenum stands out as an attractive (TH)GEM cladding material for increasing stability against secondary discharge formation. This could be beneficial for, among others, photon detectors in which operation with highly asymmetric fields above and below the (TH)GEM in a multi-foil stack geometry would allow to further reduce ion backflow. In addition to results published in NIM A (2021) 165829, new results with a full-scale molybdenum multi-hole THGEM will be discussed in the presentation.
