First Electrical Characterization of Prototype 600 A HTS Twisted-pair Cables at Different Temperatures

Following the development of twisted-pair cables prepared with High Temperature Superconducting (HTS) tapes and their initial tests at 4.2 K in liquid helium at CERN, the cable samples of 2 m lengths were subsequently tested in flowing helium gas at temperatures between 10 K and 77 K at University of Southampton. A cryostat with optimized hybrid HTS current leads was purposely built for the tests up to 2.5 kA. The cryostat has two separate helium flow conduits, each accommodating a twisted pair and allowing independent temperature control. With the completion of the tests on the twisted-pair cables, a 5 m long semi-flexible Nexans cryostat was also set up for the testing of prototype HTS links assembled at CERN. The link, which is optimized for application to the remote powering of LHC 600 A electrical circuits, consists of a compact multi-cable assembly with up to 25 twisted-pair 600 A HTS tapes. The cables are cooled by a forced-flow of helium gas the inlet temperature of which can be changed in order to compare the electrical performance over a range of temperatures. The paper reports on the results of powering tests performed on the individual cables and the integration process for the forthcoming tests of the prototype links.