Tape-to-Tape Joint Resistances of a Magnet Assembled From (RE)BCO Double-Pancake Coils

We present the results of tape-to-tape joint resistances in a 1.3-GHz/54-mm nuclear-magnetic-resonance magnet comprising a 500-MHz low-temperature-superconducting magnet and an 800-MHz high-temperature-superconducting insert (H800), which is currently in the fabrication stage at the Massachusetts Institute of Technology Francis Bitter Magnet Laboratory. The H800, which is a three-coil assembly of double-pancake coils and wound with a 6-mm-wide (RE)BCO tape (rare earth element), requires a total of 94 tape-to-tape joints. Specific results obtained are: 1) an extrapolation technique to predict the resistances of the tape-to-tape curved bridge joints from those of the curved lap joint samples with the same 6-mm-wide tape batch and joint area; 2) increased resistance owing to a small gap (<; 0.4 mm) in the outer radii of the two adjacent pancakes, which is mainly caused by the variation in the (RE) BCO tape thickness (on the order of several micrometers); 3) a method to minimize solder-heating influences on the pancake current-carrying capacity; 4) the dependence of resistance on solder materials; and 5) the experience with the 25 joints on Coil 1, which is the first of three coils for our H800 insert (H800 Coil 1).