Common Mode Effect of the ALICE Transition Radiation Detector - Baseline Shift

Elimam, Ali

Common Mode Effect of the ALICE Transition Radiation Detector - Baseline Shift

Master Thesis

2021

Abstract

The Transition Radiation Detector is a sub-detector of the ALICE experiment that is used primarily as an electron detector and a trigger mechanism. The TRD currently has 521 individual chambers distributed over 18 super modules. Each chamber houses a radiator, a drift region and a multi-wire proportional chamber with the readout electronics. When charge is absorbed in the anode wires of the multi-wire proportional chamber, it creates a common-mode effect, this common-mode effect manifests itself as a drop in the signal produced by the surrounding readout electronics where no particle has traversed, called the baseline. Capacitors have been installed in a layout to produce a low-pass filter (RC circuit) to decrease the impact of the common-mode effect. These capacitors were installed for a pad row pair, creating capacitor coupling for a high voltage supply segment. However, these capacitors were prone to failure, causing dead chambers that could not be used to acquire data for the remainder of the run, so it was decided to remove them. With their removal, the extent of the common-mode effect on the baseline had to be understood and corrected for in order to better calibrate the detector system. The University of Cape Town has one chamber, an L3C0 chamber. This chamber was used to collect two datasets with the same parameters, one with the 2.2 nF capacitors installed and the other without the 2.2 nF capacitors, to study the effect. It is found that the drop in baseline is only experienced by anode wires with the same capacitor coupling. Furthermore, it is observed that there is a linear relationship between the charge absorbed by the anode wires and the drop in baseline, thus charge absorbed by the anode wires can be summed should they have the same capacitor coupling. It is also found that the drop in baseline is 2.5 times larger in the dataset without capacitors. The final part of the thesis corrects for this common-mode effect, using a correction factor determined from the dataset

Keywords

Nuclear Power

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