Detailed analysis of the transient voltage in a JT-60SA PF coil circuit

Yamauchi, Kunihito; Shimada, Katsuhiro; Terakado, Tsunehisa; Matsukawa, Makoto; Coletti, R.*; Lampasi, A.*; Gaio, E.*; Coletti, A.*; Novello, L.*

One of the most essential issues for designing a power supply system of superconducting coil is to avoid any overvoltage. Here, the most concerned overvoltage can appear between turns due to the transiently concentrated voltage distribution inside the coil, which is mainly caused by parasitic capacitances and high dv/dt. For this reason, the coil power supply, especially fast high voltage generation circuit, should equip proper snubber(s) in order to suppress the dv/dt. However, it is too complicated to accurately evaluate the transient voltage in the coil because of the distributed parameters of the mutual inductance between turns and the capacitance between adjacent conductors. In this study, such a complicated system is modeled with reasonably detailed circuit network with lumped ones, and is integrated into the overall simulation model of JT-60SA PF coil circuit. Then a detailed circuit analysis is conducted in order to evaluate the possible voltage transient in the coil circuit. As a result, appropriate circuit parameters in the coil power supply including the snubbers are obtained.