High voltage power supply of negative-ion based NBI for JT-60U

The power supply for the negative-ion based NBI system for JT-60U is composed of negative-ion generation, extraction and acceleration power supplies. The acceleration power supply is used to accelerate negative ions up to 500 keV and has a function of power cut off within 200 /spl mu/sec for protecting the grid of the accelerator and the power supply itself by a surge voltage at the moment of ion source breakdown. A voltage holding test and a break down test were executed before beam extraction to confirm the performance of the power supply. The control system of the acceleration power supply was modified to a digital control system at the end of 1996, and therefore the rise time of the acceleration voltage up to 500 kV could decreased to about 50 msec, which is one third roughly of the original rise time with the conventional analog control system.