Mainz 2022 – scientific programme

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HK: Fachverband Physik der Hadronen und Kerne

HK 6: Instrumentation III

HK 6.5: Talk

Monday, March 28, 2022, 15:00–15:15, HK-H5

Distortions in the ALICE TPC caused by charge-up effects in the field cage — •Tim Geiger for the ALICE collaboration — Institut für Kernphysik, Goethe-Universität Frankfurt

ALICE is the dedicated heavy-ion experiment at the LHC at CERN. The main tracking and particle identification detector of ALICE is a large-volume Time Projection Chamber (TPC). To cope with the increased Pb-Pb interaction rate of 50kHz in Run 3, starting in 2022, the TPC was upgraded from multi-wire proportional chambers to a readout based on Gas Electron Multipliers (GEMs) which allows for a continuous readout of the detector.

In order to achieve its intrinsic track reconstruction resolution, a good understanding of possible space-point distortions is required. To study possible distortions, a dedicated commissioning campaign with x-ray illumination at different intensities was carried out. At the same time, a laser system was used to create ionization tracks in the TPC. The laser light also creates photo electrons at the aluminized high-voltage electrode of the drift field. Distortions in the drift time of the photo electrons are observed, varying with the x-ray intensity. This is caused by charge-up effects near the high-voltage electrode, locally modifying the electric field.

In this poster, we present an analysis of the measured distortions. They are compared to electrostatic calculations of different possible scenarios of modifications in the drift field.