Quality Assurance of GEM-based Readout Chambers for the Time Projection Chamber of ALICE

The ALICE Time Projection Chamber is the main device for tracking and particle identification. Starting from 2021, LHC will provide Pb-Pb collisions at a rate of 50 kHz, about 4 times higher than the present collision rate. Recording collisions at this rate would not be possible with the current readout scheme which is based on multi-wire proportional chambers (MWPC) with a gating grid. Therefore during the LHC long shutdown, which is scheduled for 2019-2020, the MWPCs will be replaced by readout chambers based on gaseous electron multipliers (GEMs). The new readout chambers use a stack of 4 GEMs to preserve the present energy resolution while keeping the ion backflow into the drift volume of the TPC below 1 percent. At GSI Helmholtzzentrum fuer Schwerionenforschung, half of the outer readout chambers (OROC) are assembled and their performance is checked. In this talk we will present the ongoing production and the qa procedures and their results, which ensure that all chambers meet the specifications. These include tests of the leakage current of GEM foils, the gain and ion backflow uniformity and the stability in the presence of high-level ionizing radiation, as well as the gas tightness.