Building a large-area GEM-based readout chamber for the upgrade of the ALICE TPC

TL;DR

This paper reports on the development and testing of the largest GEM-based readout chamber for the ALICE TPC upgrade, enabling higher data rates for particle detection at CERN.

Contribution

It introduces the design and successful commissioning of the largest GEM-based detector, demonstrating feasibility for the ALICE TPC upgrade.

Findings

GEM OROC is the largest GEM-based detector built to date.

The prototype was successfully commissioned with radioactive sources.

The upgrade enables the TPC to handle higher interaction rates.

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 up to 50 kHz, which is about a factor of 100 above the present read-out rate of the TPC. To fully exploit the LHC potential the TPC will be upgraded based on the Gas Electron Multiplier (GEM) technology. A prototype of an ALICE TPC Outer Read-Out Chamber (OROC) was equipped with twelve large-size GEM foils as amplification stage to demonstrate the feasibility of replacing the current Multi Wire Proportional Chambers with the new technology. With a total area of $\sim$0.76 m$^2$ it is the largest GEM-based detector built to date. The GEM OROC was installed within a test field cage and commissioned with radioactive sources.