MODELING OF THE INDUCED LOOP CURRENT IN CICC(CABLE-IN-CONDUIT CONDUCTOR) SUPERCONDUCTING MAGNET

摘要

CICC magnets under ramped magnetic field show electromagnetic instability due to current imbalance among the strands. Ramp-rate limitation is a phenomenon in which the magnet quenches prematurely before it reaches its apparent critical current. One of the main factors that cause the ramp-rate limitation is the loop current (or supercurrent). The circulating loop current is induced due to the different flux linkage of the strands in the cable. This paper describes a circuit model that can predict the maximum loop current under linearly varied dB/dt condition in the magnet. The equivalent circuit model of the strands is constructed at each twist pitch of the CICC inside the magnet. The actual local field change along the conductor in the magnet is mainly considered. According to the local field change and the twisted geometry of the strands, the loop current at sub-divided one twist pitch is first calculated. Each calculated loop current is superposed to result in the final value of the loop current in the magnet. The surface contact resistance of superconducting strands influences current circulating paths, giving a great impact on the maximum unbalanced strand current. The results of unsymmetrical twisting of strands are also quantitatively predicted to explain ramp-rate limitation of CICC.