Development of GEM-based Read-Out Chambers for the upgrade of the ALICE TPC

ALICE at the LHC at CERN is planning a major upgrade of the central barrel detectors, including the TPC, to cope with an increase of the LHC luminosity after 2018. A prototype of an ALICE TPC Inner Read-Out Chamber (IROC) was equipped with three large-size Gas Electron Multiplier (GEM) foils as amplification stage to demonstrate the feasibility of replacing the current readout by Multi-Wire Proportional Chambers (MWPC) with such technology. The GEM IROC was installed within a test field cage with a drift length of 115mm and commissioned with radioactive sources. The dE/dx resolution of the prototype was evaluated in a test beam campaign at the CERN PS and is comparable to the resolution of the MWPC IROC. Stability under LHC conditions was tested during the ALICE p-Pb beam time, when the prototype was mounted underneath LHC beam pipe, close to the interaction point.