The ECH system is under consideration to heat plasma and drive plasma current locally for JT-60SU. On the first stage, the frequency of 110GHz is proposed to inject the fundamental O-mode wave at the toroidal field of 4T. The system design is intended to operate at a pulse length of several seconds with output power of 3MW, because the design priority is to use the existing RF facility of JT-60 such as the DC power supply within several seconds operation. The 1MW gyrotron with Collector Potential Depression (CPD), which will be developed on the same technology with that of the 170GHz and 1MW gyrotron for ITER, is used in the design. The CPD technology enables to drive the gyrotron by the existing DC power supply with the voltage fluctuation of the order of %. The transmission line of the low-loss HE11 mode is used from the gyrotron to the antenna through the vacuum evacuated corrugated waveguide. The total length of the transmission line is around 60m and its loss is expected around 20%. The antenna is composed of the couple of the fixed and movable mirrors to change the deposition profile poloidaly at the injection toroidal angle of around 55 degrees to the magnetic axis.

On the second stage, the steady state operation will be done incorporating 170GHz and 1MW gyrotron at the full toroidal magnetic filed of 6T by employing a steady state DC power supply. All components are designed to be compatible for the steady state operation. A high power injection of 40MW is expected by using a large antenna which is composed of an array of 52 corrugated waveguides on final stage.