Control method and device of superconductive coil of thermonuclear device

The present invention provides a method of and a device for reducing alternating current loss upon annihilation of plasma current for the protection of coils and improvement of an operation efficiency of devices, thereby avoiding quenching. Namely, the device comprises (1) a mechanism for detecting spontaneous annihilation of plasma current, and (2) a calculation mechanism for evaluating alternating current loss and determining an aimed current value so as to provide a magnetic field distribution for reducing the alternating current loss. If the annihilation of the plasma current is detected, the change of magnetic fields with time at a position of the superconductive coils due to reduction of plasma current is forecast, and an aimed value for the current of the superconductive coils is determined so as to partially or completely eliminate the change with time. Since the existent coil current control device and a power source control the current of the coil depending on the aimed value, the alternating current loss is suppressed. Then, the superconductive coils are not quenched. (I.S.)