Modification of the JT-60 poloidal field power supply for high triangularity divertor operation

This paper describes the modification of the poloidal field power supply for the high triangularity divertor operation in JT-60. The power supply was mainly modified so as to change the combination of the thyristor converters and the poloidal field coils. After this modification. Stable divertor plasmas with a triangularity up to 0.4 at a plasma current of 2 MA were successfully obtained. However, an overcurrent of the thyristor converters in the horizontal field power supply had been often observed due to the oscillation of the voltage control command and natural commutation property of the thyristor converters in conjunction with MHD instabilities. This serious problem has been solved by introducing the rate limit control for the output voltage of the converters. In addition, it was demonstrated that both horizontal and vertical positions of the divertor X-point can be controlled simultaneously, which may be useful for the W-shaped semi-closed divertor operation