The largest gaseous Time Projection Chamber (TPC) in the world, the ALICE TPC, will be upgraded based on Micro Pattern Gas Detector technology during the second long shutdown of the CERN Large Hadron Collider in 2019/20. The upgraded detector will operate continuously without the use of a triggered gating grid. It will thus be able to record all minimum bias Pb-Pb collisions that the LHC will deliver at the anticipated peak interaction rate of 50 kHz for the high luminosity heavy-ion era. New read-out electronics will send a continuous stream of data to a new online farm at a rate of 3 TByte/s.
To keep distortions due to space charge from back-drifting ions at a tolerable level, an ion feedback of below 1 % is required. The new read-out chambers will consist of stacks of 4 GEM foils combining different hole pitches. In addition to a low ion backflow, other key requirements such as energy resolution and operational stability have to be met. A careful optimisation of the performance in terms of all these parameters was achieved during an extensive R&D program. A working point well within the design specifications was identified, with an ion backflow of 0.7 %, a local energy resolution of 12 % (sigma) and a discharge probability for irradiation with alpha particles of the order of 10^-10.
The project has now entered the production phase. The status of the various activities and results from testing GEM foils, first chambers and readout electronics will be presented.