Electric Field Optimization of 1MV DC-GIL Spacer With Surface Conductivity Gradient for ITER NBI

The flashover along epoxy spacer installed in 1 MV DC GIL caused by the excessive concentration of electric field threatens the safe operation of the ITER NBI (neutral beam injector). A spacer with surface conductivity gradient has been proposed to optimize the electric field distribution. In this paper, a simplified model of transmission pipeline with spacer is established. It is found that the electric field is mainly concentrated on the high voltage triple junction and the turning position of spacer. The surface conductivity gradient distribution on the spacer is designed by an iterative method. Results indicate that surface conductivity gradient can weaken the electric field distortion on both sides of spacer, especially the electric field strength of turning position of the concave surface is decreased obviously compared with that of the conventional spacer.