Heat transfer across dielectric-metallic interfaces and thin layers at low and ultra-low temperatures

The goal of the AEgIS experiment at CERN is the first direct measurement of the Earth's gravitational acceleration on antimatter within 1 % precision. In the framework of this project, a thermalisation strategy for a set of ultra-cold electrodes forming a Penning trap for antimatter has been investigated. Two sandwich setups have been analysed. The investigation of the first sandwich consisting of copper, indium and sapphire has demonstrated the importance of the oxide layers on the interface thermal resistance. An important conclusion has been drawn that with indium in the normal conducting state the compression force can be removed without changing the total thermal resistivity of the sandwich. The total thermal resistivity of the second setup with additional thin layers of gold and titanium shows, that the sputtering of titanium and the mechanism of its adhesion to sapphire can have a significant influence on the interface thermal resistivity. The low temperature and ultra-low temperature thermal diffusivity of the sandwich has also been measured. The results are consistent with respect to the built model over the whole temperature range. The new electrode has been designed and manufactured. A new way of clamping provides more uniform pressure distribution on the bottom surface of the electrode and increases the chances for a formation of a robust indium bond. The thermal performance of the electrode has been tested in steady state and transient conditions and it proved to be over five times higher than the performance of the old design.