Heidelberg 2015 – scientific programme
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HK: Fachverband Physik der Hadronen und Kerne
HK 13: Instrumentation 5
HK 13.2: Talk
Monday, March 23, 2015, 17:30–17:45, M/HS2
Space charge calibration of the ALICE TPC operated with an open gating grid — •Ernst Hellbär1, Marian Ivanov2, and Jens Wiechula3 for the ALICE collaboration — 1Institut für Kernphysik, Goethe-Universität Frankfurt — 2GSI — 3Universität Tübingen
The Time Projection Chamber (TPC) is the main particle identification detector of the ALICE experiment at the CERN LHC. High interaction rates of 50 kHz in Pb-Pb during the Run 3 period after 2020 require a major upgrade of the TPC readout. The currently used Multiwire Proportional Chambers (MWPCs) will be replaced by readout chambers (ROCs) based on Gas Electron Multiplier (GEM) technology which will be operated in a continuous mode. While the gating grid of the MWPCs prevents the positive ions of the amplification region from entering the drift volume, the GEM-based ROCs will introduce an ion backflow (IBF) of about 1%. In combination with the high-luminosity environment, this amount of back-drifting ions results in a considerable space charge density which distorts the drift path of the primary ionisation electrons significantly. In order to still provide a high tracking efficiency and cluster-to-track association, an efficient calibration scheme will be implemented. As a test ground for the new calibration scheme, pp collision data was taken during Run 1 with the gating grid operated in a transparent mode allowing the ions to enter the drift volume. The measured space point distortions due to the space charge will be presented together with the corrected data and compared to simulations for Run 3.
Supported by BMBF and the Helmholtz Association.