Micro-fabricated silicon devices for advanced thermal management and integration of particle tracking detectors

Since their first studies targeting the cooling of high-power computing chips, micro-channel devices are proven to provide a very efficient cooling system. In the last years micro-channel cooling has been successfully applied to the cooling of particle detectors at CERN. Thanks to their high thermal efficiency, they can guarantee a good heat sink for the cooling of silicon trackers, fundamental for the reduction of the radiation damage caused by the beam interactions. The radiation damage on the silicon detector is increasing with temperature and furthermore the detectors are producing heat that should be dissipated in the supporting structure. Micro-channels guarantee a distributed and uniform thermal exchange, thanks to the high flexibility of the micro-fabrication process that allows a large variety of channel designs. The thin nature of the micro-channels etched inside silicon wafers, is fulfilling the physics requirement of minimization of the material crossed by the particle beam. Furthermore micro-channels are well suited to be fabricated in silicon, as the same material of the detector they need to cool, and in this way mechanical stresses due to thermal gradients and different Coefficients of Thermal Expansion are minimized in the structure. The silicon micro-channel device fabrication starts with the etching of the channels in a silicon wafer, followed by the bonding of a cover wafer in silicon (or in Pyrex for testing purposes) to close the channels, and ends with the etching of the fluidic apertures for the fluid circulation. The fluid circulating inside can be in single phase or two phase flow and the flow parameters like pressure, temperature or mass flow, can vary following each detector requirements. After the micro-fabrication of the cooling devices, thermal and fluidic tests are done to validate the channels performances before integrating them in the detector structure. The mechanical integration inside the detector starts with the equipment of the device with fluidic connectors for the fluid circulation, is followed by the gluing of the detector on the micro-channels surface, and ends with the mechanical jigs and supports needed to integrate the cooling in the detector structure. The first High Energy Physics experiment pioneering micro-channel cooling was the NA62 detector who chose to cool its three GTK stations with a micro-channel plate circulating C6F14 in liquid flow. The LHCb VELO detector has chosen a CO2 evaporative flow in micro-channels for its upgrade in 2018. The ATLAS and ALICE detectors are evaluating the possibility of adopting a cooling system based on two-phase cooling in micro-channels using CO2 and C4F10 fluids respectively. Starting with the first application of micro-channel cooling, this novel cooling system applied to particle detector at CERN is fully analysed in this thesis. The four micro-channels cooling applications currently developed at CERN, are analysed in different fields: the micro-fabrication of the cooling plates, the structural properties of silicon to understand the maximum pressure a device can hold, the thermal exchange and fluid circulation to evaluate the cooling performances and, in the last part, the mechanical integration of the silicon cooling plate inside the detector infrastructure.