Discharge probability studies with multi-GEM detectors for the ALICE TPC Upgrade

TL;DR

This paper investigates the discharge probability in multi-GEM detectors used in the ALICE TPC upgrade, focusing on optimizing GEM configurations to ensure stable operation in high-rate LHC conditions.

Contribution

It provides experimental discharge probability measurements for 3- and 4-GEM prototypes, informing the optimization of GEM stack geometry and high voltage settings.

Findings

Discharge probability increases with ionization level.

Optimized GEM configurations reduce discharge occurrences.

Results support stable operation in high-rate environments.

Abstract

A large Time Projection Chamber (TPC) is the main device for tracking and charged-particle identification in the ALICE experiment at the CERN LHC. After the second long shutdown in 2019-2020, the LHC will deliver Pb beams colliding at an interaction rate of up to 50 kHz, which is about a factor of 50 above the present readout rate of the TPC. To fully exploit the LHC potential, the TPC readout chambers will be upgraded with Gas Electron Multiplier (GEM) technology. To assure stable behaviour of the upgraded chambers in the harsh LHC environment, a dedicated R&D programme was launched in order to optimize GEM stack geometry and its high voltage configuration with respect to electric discharges. We present a summary of discharge probability measurements performed with 3- and 4-GEM prototypes irradiated with highly ionising alpha particles.