Plasma Feedback Control System Design and the Results of JT-60U

This paper describes the design modifications to the plasma feedback control system, including power supply, for the Upgrade of JT-60. One of the major design issues was to be able to change the kind of control command for the thyristor converter from voltage to current and vice versa at any time during the discharge. Another one was to adopt a faster control system with 250µs response for stabilization of plasma vertical position, even in plasmas with high elongation of 1.8. These modifications improved the plasma controllability especially at initiation and made protecting the poloidal field coil system easier when the plasma disrupts. The high flexibility of the control system led to the achievement of a 4MA plasma after only 2 weeks of JT-60U operation.