10 kA Joints for HTS Roebel Cables

Future HTS high field magnets using multi-tape HTS cables need 10 kA low resistance connections. The connections are needed between the poles of the magnets and at the terminals in a wide operating temperature range, from 1.9-85 K. The EuCARD WP10 Future Magnets collaboration aims at testing HTS based Roebel cables in an accelerator magnet. Usually, LTS cables are jointed inside a relatively short soldered block. Powering tests at CERN have highlighted excess heating of a joint following classical LTS joint design. The HTS Roebel cables are assembled from REBCO coated conductor tapes in a transposed configuration. Due to this, the tapes surface the cable at an angle with the cable axis. A low-resistance joint requires a sufficiently large interface area for each tape. Within one twist pitch length, each tape is located at the surface of the cable over a relatively small non-constant area. This geometry prevents making a well-controlled joint in a compact length along the cable. This paper presents a compact joint configuration for the Roebel cable overcoming these practical challenges. A new joint called fin-block is designed. The joint resistance is estimated computationally. Finally the test results as a function of current and temperature are presented.