Thermal Conductance Measurement of Electrically Insulated Joints for Cryogenic Applications

Abstract One of the important aspects of any cryogenic design is to achieve good thermal performance by minimizing the temperature gradient at different contact regions of the thermal mass. In some cases, electrical isolation may be required at contact regions. Different combinations of the thermally conductive and at the same time electrically insulated joints have been characterized using a GM cryocooler based conduction-cooled test rig (CCR). A two stage CCR has been used to cool sample stacks down to 4 K with measured temperature differences across the sample stack up to 110 K, by increasing the 2 nd stage temperature. Different types of ceramics and polyimide (Kapton ® ) have been used as an electrical insulator, stacked in between copper blocks and a 2 nd stage copper bus bar. Ceramic materials have been coated on copper blocks with surface roughness (roughness average, R a ) that varies from 9 to 14 μm for different ceramics measured, using chromatic white light profilometry (CWLP), whereas bare copper blocks for samples and the 2 nd stage copper busbar show a milled finish roughness average of R a = 1.6 to 3.2 μm. We present a detailed, comparative study of novel thermal contact conductance measurements by using different material combinations.