Abstract
The ALICE (A Large Ion Collider Experiment) experiment at the Large Hadron Collider (LHC) at CERN is dedicated to heavy ion physics to explore the structure of strongly interacting matter. The Time Projection Chamber (TPC) of ALICE is a tracking detector located in the central region of the experiment. It offers excellent tracking capabilities as well as particle identification. After the second long shutdown (LS2) the LHC will run at substantially higher luminosities. To be able to increase the data acquisition rate by a factor of 100, the ALICE TPC experiment has to replace the Multi-Wire Proportional Chamber (MWPC) –based readout chambers. The MWPC are operated with gating grid that limits the rate to O(kHz). The new ReadOut Chamber (ROC) design is based on Gas Electron Multiplier (GEM) technology operating in continuous mode. The current GEM productions scheme foresees the production of more than 800 GEM foils of different types. To fulfill the requirements on the performance of the GEM TPC readout, necessitates thorough Quality Assurance (QA) measures. The QA scheme, developed by the ALICE collaboration, will be presented in detail.
Highlights
Each hole in a Gas Electron Multiplier (GEM) foil acts as an independent multiplication channel, enabling high resolution 2d detection of charged particles
The ReadOut Chamber (ROC) will be constructed with stack of 4 GEM foils that allow for continuous readout
In this paper we focus solely on the quality assurance (QA) of individual GEM foils but not on the QA of the ROCs
Summary
Each hole in a GEM foil acts as an independent multiplication channel, enabling high resolution 2d detection of charged particles. A drifting electron entering from the top and the electron avalanche are shown in white. The back drifting positive ions are shown in yellow. The ROC will be constructed with stack of 4 GEM foils that allow for continuous readout. The configuration can be tuned such to fulfill the design criteria, especially to maintain the present energy resolution and to have low ion feedback without the need for a gating grid. This could not be achieved with a stack of 3 GEM foils.
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