Bonn 2020 – scientific programme

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T: Fachverband Teilchenphysik

T 107: Combined instrumentation session I: Gaseous detectors (joint session HK/T)

T 107.5: Talk

Friday, April 3, 2020, 12:00–12:15, J-HS C

Propagation of discharges in a double-GEM detector — •Bogdan Blidaru for the ALICE collaboration — GSI Helmholtzzentrum für Schwerionenforschung, Darmstadt, Germany

The Large Hadron Collider will provide Pb-Pb collisions at an interaction rate of 50 kHz from 2021 onward.

In order to cope with this, the ALICE Time Projection Chamber is being upgraded. Readout chambers equipped with a stack of four Gas Electron Multiplier (GEM) foils provide a continuous readout. After installation in the ALICE cavern, the GEM chambers will be inaccessible. Thus, long-term stability and reliable readout over a time span of about 10 years is required.

One of the major challenges GEMs must overcome are electrical discharges, which can short-circuit a GEM segment and render it inactive. Some peculiar aspects of the discharge phenomena are surfacing. This talk is focused on the propagating nature of discharges, from one GEM in a stack to another.

A small detector with two 10×10 cm² GEM foils is used to study the evolution of the GEM potentials during and after discharges. Particular emphasis is put on understanding and mitigating the appearance of discharges by using decoupling resistors that substantially reduce their propagation probability.

Moreover, some new results showing that photons are not solely responsible for the propagation of discharges are discussed. A considerable number of events where the propagation is delayed by more than 300 ns are observed and studied.