A mechanism causing an additional AC loss in a large CICC coil

A large superconducting coil wound with Cable-in-Conduit (CIC) conductor ca used an additional AC loss which cannot be estimated from short conductor s ample test results, It was confirmed that the additional AC loss was genera ted by long current loops in the CIC conductor. Magnetic field decays of th e loops with various long time constants were observed through Hall probes. We propose a mechanism forming the long loops. The CIC conductor is compos ed of several staged sub-cables. If one strand on the surface of a sub-cabl e contacts with the other strand on the surface of the adjacent sub-cable, the two strands must encounter each other again at LCM (Least Common Multip lier) distance of all staged cable pitches and thereby result in forming a pair of a long loop. We traced each strand in the CIC according to a method that the sub-cables at all sub-stages rotate around a center of inertia. T he long time constants were calculated and their results ran explain the da ta measured in a large SMES coil. The proposed mechanism is effective for e stimating the additional AC loss in the coil.