Interaction between the Helical Goil Current and the Toroidal Plasma Current in the Large Helical Device

The current of the superconducting helical coils is affected by the change of the toroidal plasma current in the Large Helical Device due to the tight magnetic coupling between the helical coils and the toroidal plasma current as well as to the relatively slow response of the present PID control of the DC power supplies. Since the helical coils are operated in a marginally stable condition, where a finite and temporal propagation of a normal-zone is allowed, it is important to precisely evaluate the deviation of the coil current due to the change of the toroidal plasma current. The temporal change of the helical coil current is also examined by incorporating a simple circuit equation.