Conceptual design of the quench protection circuits for the JT-60SA superconducting magnets

Gaio, E.*; Novello, L.*; Piovan, R.*; Shimada, Katsuhiro; Terakado, Tsunehisa; Kurihara, Kenichi; Matsukawa, Makoto

This paper deals with the conceptual design of the Quench Protection Circuits (QPC) of JT-60SA which have to provide a fast removal of the energy stored in the superconducting coils in case of quench. The core of the QPC units is constituted by a dc current breaker, which diverts the coil current into a resistor for a fast machine de-energization. In this paper, a hybrid solution, composed of a mechanical bypass switch paralleled to a static switch based on Integrated Gate Commutated Thyristor (IGCT) technology, has been chosen and worked out; a pyrobreaker is added in series to the hybrid switch as a backup protection. The resulting design allows benefiting from the fast breaking and very low maintenance requirement of the static switches, besides maintaining the advantage of the much lower power losses of the mechanical bypass in normal operation.