Frankfurt 2014 – wissenschaftliches Programm

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HK: Fachverband Physik der Hadronen und Kerne

HK 43: Instrumentierung

HK 43.3: Vortrag

Donnerstag, 20. März 2014, 14:45–15:00, HZ 8

Ion back flow and energy resolution in GEM detectors for the ALICE TPC — •Esther Bartsch, David Just, Rainer Renfordt, and Harald Appelshäuser for the ALICE collaboration — Institut für Kernphysik, Goethe-Universität Frankfurt

For the upgrade of the Time Projection Chamber (TPC) of the ALICE experiment at the CERN LHC it is planned to replace the multiwire proportional readout chambers by Gas Electron Multiplier (GEM) stacks. The high interaction rate of 50 kHz foreseen for the Run 3 period of the LHC makes a readout scheme desirable that can accommodate the 100 times higher rates. GEM-based readout chambers that can be operated in continuous mode are the prime candidate. However, the backflow of positive ions into the detector volume turns out to be too high in commonly used triple-GEM stacks, producing unacceptable levels of space charge and thus distortions of the drift field. Several measures to reduce the ion back flow (IBF) can be taken: addition of a fourth GEM foil, optimization of the GEM voltages and transfer fields between the foils.

A dedicated test detector for the characterization of triple and quadruple GEM stacks was set up at the IKF in Frankfurt. The results of systematic studies of the IBF and the energy resolution in different arrangements of standard and large-pitch GEM foils will be presented.

Supported by BMBF and the Helmholtz Association.