Radio frequency source for JT-60

Japan Atomic Energy Research Institute has been conducting radio frequency heating experiments with a critical plasma experiment system called JT-60. The radio frequency heating system for JT-60 consists of three LHRF (lower hybrid range of frequency) heating units and one ICRF (ion cyclotron range of frequency) heating unit. Each LHRF heating unit has eight large-power klystrons to give an oscillator output of 8 MW. The RF signals (around 2 GHz) generated is divided into two: one is sent to the level controller and the other is used for phase detection. The level controler acts to control the RF power level and cut the RF power after receiving an interlock signal from an on/off controller. The main circuit output signal from the level controller is divided into 8 x 2, after amplified up to about 1 MW. Eight of them are used as reference signal for automatic gain control while the others serving as phase control signal for the main circuit. The ICRF heating unit, on the other hand, consists of eight amplifying units, each with a final output of 750 kW. Two final outputs are combined into 1.5 MW and sent to the tokamak system. The exciter component is composed of a signal generator, level controller, reference level generator, divider, phase controller, and amplitude/phase controller for exciting the 750 kW amplifying units. (Nogami, K.)