Design of an Insert to Characterize Superconducting Materials at 4.2 K Using a Cryocooler System.

摘要

High Temperature Superconductors (HTS) are potential candidates in magnet design for high energy physics and fusion reactors due to their high electrical performance in high magnetic fields. It is necessary to characterize HTS conductors at 4.2 K so that their properties are well known for use in magnet applications.;This work focused on the design, analysis and testing of an experimental probe able to measure the critical current of high temperature superconductors at low temperatures (down to 4.2 K). The test probe was designed for use in a two stage Gifford-McMahon Helium gas cryocooler. The probe provides the necessary flexibility so that different measurements can be performed for the electromechanical characterizations of superconductors: critical current, Residual Resistivity Ratio (RRR) and mechanical loading effects.;Preliminary cool down experiments showed that the cryocooler was incapable of reaching the desired temperature of 4.2 K with the experimental probe mounted inside. An analytical study of the system was undertaken to identify the potential causes of those results. Heat conduction was found to have the major effect on the temperature of the structure. A finite element analysis was conducted in parallel with experiments to further investigate the heat conduction effect and to identify the thermal limitation of the system. Copper and G10 rods were tested to evaluate the thermal response of materials with different thermal conductivity. Experiments were also conducted on the test probe with a few structural modifications (reduction of the number of support rods and the addition of radiation shields). The results showed that even though using materials with low thermal conductivity helps achieve lower temperatures, heat conduction along the structure prevents the system from reaching temperatures as low as 4.2 K.