Interpretation of conduit voltage measurements on the poloidal field insert sample using the CUDI-CICC numerical code

The results of simulations with the CUDI-CICC code on the poloidal field insert sample (PFIS) tested in the SULTAN test facility are presented. The interpretations are based on current distribution analysis from self-field measurements with Hall sensor arrays and current sharing measurements. The possible variation in voltage-current (VI) curves among the sub-cables in the PFIS caused by the cable self-field and joint non-uniformity is a principal issue for the evaluation of the strand-to-cable performance. The cable transverse voltages, initiated by current non-uniformity in a cabled conductor, can affect the shape of the longitudinal VI curve. The basic cable data are obtained by petal-to-conduit contact resistance and conduit resistivity measurements under transverse cyclic load in the Twente Cryogenic Cable Press. We assessed the impact of the conduit, the sub-cable resistive barrier wraps and the location of the voltage taps on the measured voltage, and some comparisons were carried out with experimental runs on the PFIS. The outcome confirms that the transverse voltages, caused by current redistribution, do affect the shape of the VI transition. This effect seems particularly important in short sample tests. Moreover, it is demonstrated that the location of the voltage taps can affect the experimentally obtained VI curve and solutions for most accurate measurement of the VI are discussed in the paper. The numerical model, CUDI-CICC covers the final cabling stage of inter-petal interactions only, by which the possible role of intra-petal non-uniformities is ignored, although recognized as potentially relevant.