Thermal Characterization and Optimization of the Pixel Module Support Structure for the Phase-1 Upgrade of the CMS Pixel Detector

The CMS (Compact Muon Solenoid) pixel detector is used in CMS for the vertex reconstruction of events in high-energy proton-proton collisions produced by the Large Hadron Collider (LHC). It is planned for the future years that the LHC will deliver significantly higher instantaneous and integrated luminosities. Therefore, also the demands and requirements for the participating detectors rise. Thus the current CMS pixel detector will be replaced by the CMS Phase-1 Upgrade Pixel Detector in the extended year-end technical stop in winter 2016/2017. As a vertex detector, the pixel detector is the innermost detector component and it is located at a short distance to the proton-proton interaction point. Therefore it has to cope with high particle hit rates and high irradiation. The heat produced due to power consumption has to be removed while using a low-mass detector design. The low-mass design of the Phase-1 Upgrade Pixel Detector will be implemented by utilizing a new two-phase CO2 cooling concept and an ultra light-weight carbon fiber support structure. This allows for a lower material budget than in the current detector. Although the two-phase CO2 cooling concept is a very efficient system, a sufficient cooling of the new pixel detector still represents a challenge. One has to deal with very small cooling contact surfaces (≈ 1.8mm diameter cooling pipes) and materials with bad thermal conductivity (through-plate conductivity of carbon fiber plates). In this thesis, the mechanics of the Phase-1 Upgrade Pixel Detector is characterized by measurements in terms of thermal performance and the components with most potential for an optimization of the cooling performance are pointed out. Based on Finite Element simulations, an optimized mechanics is developed and thermally tested. The results are compared to the expected power consumption of the upgrade detector and an estimation of the cooling performance with the optimized mechanics is presented.