A large Time Projection Chamber (TPC) is the main device for tracking and particle identification in the ALICE experiment at the Large Hadron Collider (LHC) at CERN. In the upcoming Run 3, the LHC will deliver lead beams colliding at an interaction rate of up to 50 kHz. In order to read out all minimum bias events in Pb–Pb collisions, the TPC was upgraded with an amplification stage based on Gas Electron Multipliers (GEM) and new front-end electronics. With the new amplification stage, a trigger-less operation of the TPC becomes possible, resulting in a continuous readout without dead time.
The exchange of the readout chambers and front-end electronics took place in a dedicated clean room in 2019/20. The upgraded TPC was then moved back to its designated position at the interaction point 2 of the LHC and an extensive commissioning programme was carried out. It includes, inter alia, noise studies, measurements of laser tracks, irradiation of the TPC with an intense X-ray source, the flushing of radioactive 83mKr into the active volume and the operation during the first proton–proton collisions provided by the LHC. During these measurements, the TPC operated at nominal conditions and the continuous readout capability was tested successfully.