Abstract
We are developing conduction-cooled REBCO superconducting coils. We first observed thermal runaway currents of the coils during the process of making impregnated single-pancake coils with an outer diameter of 300 mm with REBCO- coated conductors and conduction-cooling them using a GM cryocooler. In addition, we performed a numerical simulation of the electromagnetic and thermal behavior of the coils with the critical current properties of the REBCO tapes through use of a threedimensional heat conduction equation. Comparing the observed results with the theoretical prediction, we confirmed the theoretical predictability of the thermal runaway currents of the single-pancake coils. These results suggest that the winding and impregnation were successfully carried out without degradation of the properties of the prepared REBCO tapes. Further, in testing conducted on an impregnated small coil in a 4 T background magnetic field, we confirmed that the impregnated coils could withstand hoop stress as high as the mechanical strength of the REBCO tape itself.
