SPIDER is the full scale prototype of the RadioFrequency driven negative Ion Source (IS) of the ITER Heating Neutral Beam Injector. It is equipped with a system of grids, each having 1280 apertures, composed of the Plasma Grid (PG) polarized up to -108 kV with respect to ground, the Extraction Grid (EG) polarized up to -96 kV with respect to ground and the Grounded Grid (GG). The negative ions are mainly produced by the interaction of plasma with the PG surface which is heated up to 150°C and covered with a caesium layer. Recently the opportunity to explore the operation with a range of vessel pressures wider than the original requirements has been identified and, in view of an upgrade of the pumping system, a temporary solution consisting in a PG mask with a limited number of apertures was conceived. This solution will allow the beam operation of SPIDER, although at reduced ion beam current, in a configuration that permits the investigation of the beam optical parameters. The PG mask will be held in position by means of about 100 PEEK insulating supports, called pushers, hooked to a stainless steel frame at the GG potential; they pass through the GG and the EG apertures and push the mask on the PG. With this temporary solution the EG and PG can be biased up to -30 kV and -34 kV respectively. This paper deals with the design of a testbed capable of reproducing the working conditions of the pushers in SPIDER (electric field, vessel pressure, magnetic field and PG temperature), in order to verify the voltage hold off of some pusher prototypes, and reports on the results of the relevant experimental campaign.
Voltage Hold Off Test of the Insulating Supports for the Plasma Grid Mask of SPIDER
Recchia M;Serianni G
2019
Abstract
SPIDER is the full scale prototype of the RadioFrequency driven negative Ion Source (IS) of the ITER Heating Neutral Beam Injector. It is equipped with a system of grids, each having 1280 apertures, composed of the Plasma Grid (PG) polarized up to -108 kV with respect to ground, the Extraction Grid (EG) polarized up to -96 kV with respect to ground and the Grounded Grid (GG). The negative ions are mainly produced by the interaction of plasma with the PG surface which is heated up to 150°C and covered with a caesium layer. Recently the opportunity to explore the operation with a range of vessel pressures wider than the original requirements has been identified and, in view of an upgrade of the pumping system, a temporary solution consisting in a PG mask with a limited number of apertures was conceived. This solution will allow the beam operation of SPIDER, although at reduced ion beam current, in a configuration that permits the investigation of the beam optical parameters. The PG mask will be held in position by means of about 100 PEEK insulating supports, called pushers, hooked to a stainless steel frame at the GG potential; they pass through the GG and the EG apertures and push the mask on the PG. With this temporary solution the EG and PG can be biased up to -30 kV and -34 kV respectively. This paper deals with the design of a testbed capable of reproducing the working conditions of the pushers in SPIDER (electric field, vessel pressure, magnetic field and PG temperature), in order to verify the voltage hold off of some pusher prototypes, and reports on the results of the relevant experimental campaign.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
