M. Sawahata

Development and achievements on the high power ECRF system in JT-60U

An output power of 1.5 MW for 1 s was achieved at 110 GHz in a recent gyrotron development using the JT-60U ECRF system. It is the worlds highest power oscillation for a pulse duration of at least 1 s. The achievement was enabled by, in addition to the carefully designed cavity and collector, necessary because of thermal stress, an RF shield for the adjustment bellows and a low-dielectric-loss dc break. The way the power was modulated was improved upon by controlling the anode voltage, with high modulation frequency of 5 kHz being achieved in NTM stabilization experiments. Moreover, as a developmental step to realizing a reliable ECRF system for use in future fusion experiments, a long pulse demonstration of 0.4 MW and a 30 s injection into the plasma was achieved with real time control of the anode/cathode-heater. Confirmation was made that the temperature of the cooled components had been saturated with no evidence of any damage being discovered in the waveguides and antenna without forced cooling. An innovative antenna with a relatively wide range of beam steering capabilities utilizing a linearly moving-mirror concept was also designed for use as an active cooling antenna with longer pulses in the future, e.g. for JT-60SA. The beam profile and mechanical strength analyses proved the feasibility of the antenna.

Oscillation Control of the JT-60U High Power Gyrotron by Controlling the Anode Voltage

Tne JT-60U gyrotron has a triode electron gun, which enables to control its oscillation output by adjusting its anode voltage. The output was successfully recovered by anode voltage control when it was terminated. Moreover, the output was modulated at 0.7 MW up to 500 Hz with modulation factor 80 %.