Power supply system for large negative ion sources: Early operation experience on the SPIDER experiment

In the road-map for a fully operational ITER Neutral Beam Injector (NBI), SPIDER represents a necessary step to test its negative ion source design since the required performances have never been achieved simultaneously by any previous experiment. The smaller scale of SPIDER to the full ITER NBI prototype (named MITICA, which will operate in the same test facility in Padova) allows more flexibility in the experiments and, taking advantage of its larger set of diagnostic, will provide insightful results for the entire project development. This paper is the result of the experience gained within the first two years of SPIDER operation, with the focus on the Ion Source and Extraction Power Supply (ISEPS) system. A review of the system development, of the main outcomes of the first experimental phase and the description of the still open issues, is provided.