Evaluation of a cryostable low-loss conductor for pulsed field applications

A cryostable, low loss conductor as the basic strand in a 50 kA cable for a 20 MJ prototype, tokamak induction heating coil has been developed, fabricated, and evaluated. The conductor has a copper matrix multifilamentary NbTi core surrounded by a CuNi ring and stabilizing copper segmented by radial CuNi fins. Pulsed loss measurements have been made up to 2.2 T and for decay times from 0.7 to 278 ms. Measurements made on samples with various twists and portions etched away have allowed accurate evaluation of the loss components. Stability measurements were also made on insulated and uninsulated single strands and on sub-cables. Measured recovery heat flux for the bare strand is about 0.3 W/cm²; however, the application of a 0.0005 in. layer of Omega insulation increases the value to about 0.5 W/cm².