Cryogenic Thermal Studies on Terminations for Helium Gas Cooled Superconducting Cables

Details of the design of terminations for testing a superconducting DC monopole cable cooled with gaseous helium are presented. The termination design includes a liquid nitrogen chamber to reduce heat influx into the helium section through current leads. Thermal studies on the assembly of the two terminations and a 1 m or 30 m cable cryostat were performed at variable mass flow rates of helium gas. Measurements of temperature profile for the test system without the superconducting cable showed temperature rise between 5 K and 20 K depending on the mass flow rate. The temperature profile across the test system was used to estimate the heat load from different components of the system. Results with and without the liquid nitrogen in current lead section were compared to estimate the savings provided by the liquid nitrogen on the head of the helium circulation system. Suggestions for improving the design to enable fully gas cooled terminations are presented.