Long pulse production of high current D− ion beams in the JT-60 negative ion sourcea)

The first long pulse production of high power D− ion beams has been demonstrated in the JT-60 U negative ion sources, each of which was designed to produce 22A, 500keV D− ion beams. Voltage holding capability and the grid power loading were examined for long pulse production of high power D− ion beams. From the correlation between voltage holding and the light intensity of cathodoluminescence from the Fiber Reinforced Plastic insulators, the acceleration voltage for stable voltage holding capability was found to be less than 320–340kV where the light was sufficiently suppressed. By tuning the extraction voltage, the grid power loadings in the ion sources were decreased to the allowable levels for long pulse injection without a significant reduction of the beam power. After tuning the acceleration and extraction voltages, D− ion beams of 12.5 and 9.8A were produced at 340keV with cesium seeding at a rate of ∼14μg∕s into the ion sources. The pulse duration of these D− ion beams was extended step by step, an...