Experimental and Equivalent Circuit Analysis Approach to Estimate Contact Resistances on Different Sections in a D-Shaped NI HTS Coil

With well-known self-protecting behaviors of no-insulation (NI) high temperature superconductor (HTS) coils, their performance was verified by numerous high field magnets. As one of the initial investigations of the NI HTS technique being applied to toroidal field (TF) coils, an equivalent circuit analysis is carried out on a D-shaped NI HTS coil to predict its electromagnetic behaviors regarding the contact resistance, one of the most important parameters for NI HTS coils. A charging/discharging test is performed at 77 K to obtain the experimental data for contact resistance estimation. Using the measured voltage and the pressure dependency of surface contact resistivity, a combination of contact resistance is obtained through the modified lumped circuit and the partial element equivalent circuit simulation by which the shape-dependent contact resistance can be estimated. The results are expected to provide a source for careful management in the design stage to consider the uneven contact resistance and possible uneven electromagnetic behavior among different sections of the TF coil.