Low boil-off HTS current leads

HTS based leads have established themselves for high current carrying applications. This work revisits the issues for commercial magnets with a view to minimizing heat load and space for both the resistive and HTS parts. The paper describes the experimental work carried out to develop up to 300 A HTS current leads for Oxford Instruments' Cryofree and liquid helium cooled magnets. The current-voltage, temperature, and quench measurements are reported. The leads make use of BSCCO-2223 HTS wire and have been characterized at 4.2 K, 77 K, and some intermediate temperatures for quench purposes to test their robustness. The leads are in thermal equilibrium with their environment and require no additional cooling, unlike in the case of large current leads for accelerator magnets. The current work on the combined resistive and HTS parts has achieved a boil-off of 20 ml/hr in a liquid cooled cryostat.