Electric Field Regulation Along Post Insulator in DC-GIL for ITER Neutral Beam Injector

This paper presents a solution for the regulation of electric field along the post insulator of 1 MV DC GIL for ITER neutral beam injector (NBI). To regulate the electric field distribution, a simulation model of the post insulator with surface nonlinear conductivity is developed. The actual working conditions of NBI GIL including a square wave voltage, a radiation environment as well as surface charge accumulation are considered. The results show that radiation will lead to a significant increase in the conductivity of SF6 gas, which makes the heteropolar charges from the SF6 gas domain dominate the surface charge. The tangential electric field on the insulator surface is seriously distorted by heteropolar charges. The post insulator with the design of surface nonlinear conductivity can effectively dissipate the surface charge and the tangential electric field along the insulator surface can be reduced by up to 46.5%. This paper aims to propose research methods and feasible means for the reasonable insulation design of NTER GIL to ensure the safe and stable operation of ITER.