Critical issues of HV dc vacuum and pressurized gas environments for the ITER NB injector

The design of the ITER NB injector involves challenging problems related to the high voltage (HV) dc insulations, which is realized with different media, such as pressurized gas and vacuum either with or without solid insulators. For each type of insulation different physical models have to be used for the design of the components, because different mechanism can lead to a breakdown. In this paper all the recognised critical issues for the reliability of the injector HV insulation are described. We are also reporting on the literature studies and the closely related experimental observations and results of the SINGAP test bed injector. Moreover results of finite element (FE) models which simulate the insulating system of the 1 MV bushing, taking into account different HV dc regimes, are presented.