Progress on design and manufacturing of dc ultra-high voltage component for ITER NBI

Toward the 1 MV power supply system for the ITER neutral beam injector consisting of various components with oil insulation, gas insulation and vacuum insulation, design and manufacturing of dc ultra-high-voltage component have been progressed. Thermal design of long transmission line up to 100 m was established. In order to design the high-temperature water channel for the plasma grid at 1 MV potential, the resistivity of high-purity water at 180 °C was measured for the first time. With the obtained resistivity, realistic high-temperature water circulating system was designed. A high-voltage bushing to transmit multiple voltages simultaneously has been also developed through a careful experimental study on vacuum insulation characteristics with multi-gaps coaxial electrodes. With the empirical scaling the electrostatic screen was designed taking into account effect of multi-gap and expected deformation such as thermal elongation during operation. After the assembly, stable voltage holding of 240 kV at each stage was confirmed in the manufactured HV bushing.