Modeling of epoxy resin spacers for the 1 MV dc gas insulated line of ITER neutral beam injector system

The spacers for the Gas Insulated Transmission Line for the ITER neutral beam injector will be designed to withstand the operating voltage of 1 MV dc. Electric charging processes of the spacer surface are then expected to play an important role in the final electric field distribution. Aim of the paper is to investigate the effects of the different conductivity properties of the SF6-Spacer insulating structures on the surface charge set-up, and to identify a procedure to minimize this charge. Based on the most updated literature, the paper presents and discusses the results of two newly developed simulation tools: the first consisting of a quasi-static non linear model for epoxy spacer based on finite element method code ANSYS™, the other consisting of a spacer profile optimization package, whose kernel is based on a genetic algorithm. The numerical tools have been applied to post and disk spacer models of the gas insulated line; in particular, the optimization package has been used on the disk spacer, and the comparison between un-optimized and optimized spacer in terms of electric charge accumulated are presented and discussed.