SPIDER high voltage bushings: Design, development and first experimental tests

The ITER project requires at least two Neutral Beam Injectors (NBIs), each accelerating to 1 MV a 40A beam of negative deuterium ions, to deliver to the plasma a power of about 33 MW for one hour as additional heating. The fulfilment of such demanding performances required the realization of the full size prototype of the negative ion source (SPIDER - Source for Production of Ion of Deuterium Extracted from RF plasma), as well as the full size prototype of the whole 1 MV ITER injector (MITICA - Megavolt ITER Injector & Concept Advancement) at PRIMA, the test facility for the ITER neutral beams now under construction at the Consorzio RFX in Padua, Italy. The SPIDER plasma source- housed in a stainless steel vessel maintained in high vacuum - is polarized at 112 kV (12 kV extraction voltage and 100 kV accelerating voltage), so that the vacuum vessel must be equipped with three large alumina feedthroughs, ring shaped insulators (820 mm in diameter) necessary to supply the electric, hydraulics gas and diagnostic services to the plasma source. These insulators (bush- ings) belong to the most critical items in the SPIDER assembly and they required a particular effort in designing, manufacturing and testing. This paper gives an overview of the insulator design, development, manufacturing activities and presents the results of the high voltage acceptance tests.