Use of a Thermal Grid to Increase Thermal Runaway Current for REBCO Pancake Coils Operated at 77 K

During the excitation of REBCO coils, premature thermal runaways occur. In the worst case, the conductor melts down. Premature thermal runaway is caused by partial conductor degradation in the coil winding, which sometimes occurs in coils fabricated from REBCO-coated conductors. In this paper, we have examined the use of a “thermal grid” method using a polyimide electro-deposited conductor and highly thermal conductive metal sheets as a countermeasure against premature thermal runaway. This thermal grid method increases the thermal runaway current for coils with partial conductor degradation. In addition, in the case of an actual thermal runaway, the use of a thermal grid suppresses the peak temperature reached by the coil.