Baseline Design of the Cryogenic System for EURECA

Dark Matter appears to dominate the matter in the Universe. EURECA (EUropean Rare Event Calorimeter Array), a large European collaboration, was set up to discover and study directlyWeakly Interacting Massive Particles (WIMPs), which are the main candidates for non-baryonic Dark Matter. Therefore, a large mass of several tons, consisting of the detector and the support structure needs to be cooled by a dilution refrigerator to a temperature of 10 mK. The requirement for an ultra-low radioactivity prohibits the use of a heat exchanger made of sintered silver, which so far is the only material to achieve the required very high cooling power at very low temperature. Design studies of several critical components of the cryogenic system, such as the main shielding, the fast exchange of detector material and the proximity cryogenics, have been accomplished and the most suitable solutions were determined to meet the scientific requirements. For a reliable prediction of the required cooling power of the large detector array of EURECA, the residual heat load was experimentally studied and analysed. The techniques for sintering very fine copper powder have been optimized and the results are experimentally characterized and analysed. Within the frame of this thesis project, a baseline design of the cryogenic system of the EURECA Dark Matter detector array has been developed. Based on the measurements, the optimised heat exchanger made of f ine copper powder was found capable to achieve the required cooling power at the lowest temperature, which has been determined for the described design of the dilution refrigerator