System Tests and Qualification of Pixel Modules and DC-DC Converters for the Phase-1 Upgrade of the CMS Pixel Detector

The CMS experiment at the Large Hadron Collider (LHC) features a silicon pixel detector that measures tracks of charged particles. Due to continuous improvements of the LHC, the instantaneous luminosity already reached twice the original design value of 1 x 10$^{34}$cm$^{-2}$s$^{-1}$ during the so-called Run 2. In order to benefit from the additional data, the CMS collaboration has developed a new pixel detector, which has an additional fourth layer of pixel modules in the central area and an additional third layer in the endcaps, as part of the Phase-1 upgrade. Improved readout electronics increased the data acquisition efficiency. The new detector was installed in the experiment in March 2017. Within the scope of this work, the quality assurance of pixel modules, which were built by the Karlsruhe Institute of Technology for a part of the central detector, was performed. A setup for thermal cycling and electrical testing, as well as an X-ray setup for high-rate tests and an energy calibration, were developed for this purpose. In this thesis, the setups and test procedures are presented, and the results of the pixel module qualification are discussed. Out of 409 pixel modules produced, 343 (84%) were classified usable for the detector. A large part of the pixel modules (43 of 48) that were ultimately rejected did not pass the test in the X-ray setup. The power consumption of the Phase-1 pixel detector has approximately doubled compared to the original detector, making a new powering scheme necessary. In order to reduce voltage drops and power losses on the supply cables, radiation tolerant and magnetic field resistant DC-DC converters are used within CMS to provide the supply voltages for the readout chips. In this thesis, the proper function of the novel powering scheme is demonstrated. The integration tests and system tests that were performed for this purpose are described. The powering with DC-DC converters did not impair the performance of the pixel modules. For example, it was demonstrated that the detection efficiency during irradiation with photons at a rate of 120 MHz cm$^{-1}$ is about 99.2%, even when DC-DC converters power the pixel module. In addition to the performed tests, the procedures for operating the DC-DC converters in the pixel detector were developed and optimal operating parameters determined. In October and November 2017, about 5% of the installed DC-DC converters failed during operation of the pixel detector. All DC-DC converters were extracted from the pixel detector and examined in winter 2017/2018. Damage was found in about 30% additional devices. In this thesis, the troubleshooting is described, and the cause of the defects is discussed. All DC-DC converters have been replaced by newly produced ones. This thesis describes the quality assurance tests that were performed and presents the results. By the time of writing of this work in October 2018, no DC-DC converters have failed. About 109 fb$^{-1}$ of collision data have been recorded with the new pixel detector. This already exceeds the amount of data collected by the original pixel detector during its entire lifetime.