Investigation of Current Flow between Turns of NI REBCO Pancake Coil by 2-D Finite-Element Method

The no-insulation (NI) winding technique for an NI ReBCO pancake coil is expected to improve dynamic and thermal stability and enhance current density. The investigations on electromagnetic and thermal behaviors are important for the development of NI ReBCO coils. Many stability investigations of the NI ReBCO coil itself have been carried out by experiments and simulations. However, the detailed behavior of the bypass current between turns has not been shown. Although contact resistivity was obtained through prior experiment, it included the resistivity of not only contact surface but also the components, i.e., the copper stabilizer and the Hastelloy substrate, of a ReBCO tape. To investigate the detailed bypass current behavior in this paper, the true contact surface resistivity is taken into account in the simulation. The bypass current on the cross section of the NI ReBCO tape is simulated using the two-dimensional finite-element method. From the simulation results, the influence of the coil-radial resistivity between turns on the turn-to-turn contact surface resistivity is clarified. In addition, the heat loss is also reported, and a simple equivalent circuit of the turn-to-turn contact is proposed.