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

摘要

A large Time Projection Chamber (TPC) is the main device for tracking andcharged-particle identification in the ALICE experiment at the CERN LHC. Afterthe second long shutdown in 2019-2020, the LHC will deliver Pb beams collidingat an interaction rate up to 50 kHz, which is about a factor of 100 above thepresent read-out rate of the TPC. To fully exploit the LHC potential the TPCwill be upgraded based on the Gas Electron Multiplier (GEM) technology. A prototype of an ALICE TPC Outer Read-Out Chamber (OROC) was equipped withtwelve large-size GEM foils as amplification stage to demonstrate thefeasibility of replacing the current Multi Wire Proportional Chambers with thenew technology. With a total area of $\sim$0.76 m$^2$ it is the largestGEM-based detector built to date. The GEM OROC was installed within a testfield cage and commissioned with radioactive sources.