Thermal Studies on the BTL Readout Module for the CMS Phase II MIP Timing Detector

To prepare for the increase in number of particle collision interactions per bunch crossing within the high luminosity version of the Large Hadron Collider (HL-LHC), the CMS experiment is undergoing multiple concurrent upgrades. These include the addition of the MIP Timing Detector (MTD), a new layer that allows for four-dimensional particle vertex reconstruction with a time resolution of 30 picoseconds. The MTD is subdivided into a barrel section (BTL) and an endcap section (ETL). The BTL uses LYSO crystals with Silicon Photomultipliers (SiPM) photo detectors as sensors. The readout modules in the BTL must be cooled and thermally optimized to reduce radiation induced dark current in the SiPMs, which negatively affects the achievable time resolution. This talk will explain some of the results from an ongoing prototype testing that models the performance of the sensors and the cooling system for the BTL. Assorted thermal conduction materials were tested under varying conditions within this setup with special focus on the thermal contact between the SiPM array and the copper housing. The experiment was also modeled using SOLIDWORKS Thermal Simulation software, which allowed for quantifiable measurement of the thermal resistance values between the different components of the assembly.