Voltage hold off test of the insulating supports for the plasma grid mask of SPIDER

A temporary mask with a limited number of apertures for the Plasma Grid (PG) of SPIDER, the full scale prototype of the Ion Source of the ITER Heating Neutral Beam Injector, was conceived to explore SPIDER operation with a range of vessel pressure larger than the original requirements. The voltage hold off of PEEK insulating supports, called "pushers", which held in position the PG mask was experimentally verified on a testbed capable of reproducing the working conditions of the pushers in SPIDER (electric field, magnetic field, vessel pressure and PG temperature). This paper deals with the design of the testbed and reports on the results of the relevant experimental campaign.