Control device for helical system

There are disposed a means for detecting a plasma-circulating current and a rectifier for applying an inverse voltage in the direction offsetting the generated plasma current, upon transient change of a helical coil current or polloidal coil current or upon change of plasma temperature change. Since a voltage is caused in a toroidal direction of plasmas corresponding to the secondary coils of the rectifier, the plasma current based on the voltage is detected by a detecting coil such as a one-turn coil and a Rogowskii coil and an integrator. Then, the coil current is controlled so that the plasma electric current is always reduced to zero. As a result, an equilibrium magnetic field can be changed without flowing a current to plasmas by, for example, applying heating operation during operation of the helical system even in a case where the state of the plasmas is changed. Accordingly, satisfactory plasmas can be maintained by the presence of the plasma electric current without worsening the plasma characteristics. (N.H.)