Upgrade of the ALICE Time Projection Chamber for the LHC Run3

Abstract

ALICE, one of the experiments at the Large Hadron Collider (CERN), is undergoing ambitious upgrades during the ongoing second long shutdown (LS2). The main goal of this project is to access rare events and previously inaccessible physics observables. The increased Pb-Pb and pp collision rates need a correspondingly higher TPC operation rate in the next Run 3 of the LHC. The operational gated MWPC readout used so far cannot be used at such fast rates. Therefore a new readout chamber is needed with a novel technology and without any compromise on the momentum and energy resolution. As a solution the Gas Electron Multiplier (GEM) technology is applied. This new readout chamber consists of inner-(IROC) and outer (OROC) readout chambers with a 4 stage GEM cascade in order to reduce back-drifting ion space charges. These quadruple stacks have proven to provide sufficient ion blocking capabilities. This structure also preserves the intrinsic energy resolution and keeps the space-charge distortions at a tolerable level. The GEMs cannot be repaired during operation, therefore to minimize the unsuitable foils, the Quality Assurance system is developed. These cleanroom measurements investigate the hole size uniformity, the gain uniformity and the electrical stability. Due to the continuous readout, higher readout rate is possible. The new ASIC-SAMPA has been developed for this purpose. After the ROC assembly some of chambers were tested in the ALICE cavern, and a test campaign started for the further testing of the ROC bodies at GIF at CERN.