Design and Experimental Characterization of the Prototype of NIO1 High Voltage Power Supply Protection System

3PB8 Design and Experimental Characterization of the Prototype of NIO1 High Voltage Power Supply Protection System Mauro Recchia 1 , Bruno Laterza 1 , Gianluigi Serianni 1 , and Marco Cavenago 2 1 Consorzio RFX 2 INFN-LNL The Negative ion sources are a key component of the Neutral Bea m Injector for ITER, the world largest experiment to prove the feasibility of fusion as a source of energy. The requirements for the ITER NBI, to inject into the plasma 40 A of negative ion energized at 1 MV for one hour, are never been met all together, thus it was recognized the need to develop a test facility named PRIMA (Padova Research on ITER Megavolt Accelerator) including two experiments: SPIDER, a full size ITER NBI ion source and MITICA, the full scale prototype of the 1 MV ITER NBI, now under construction in Padova Italy, at Consorzio RFX premises. NIO1 (Negative Ion Optimization phase 1 ) is another experiment being developed in parallel; it is a reduced size so urce of negative ions equipped with a high voltage electrostatic grid system for beam extraction and acceleration. The negative ions are generated via radio frequen cy at 2 MHz with 2.5 kW rated and the high voltage stages are fed respectively by a 10 kV voltage 0.6 A current Extraction Grid Power Supply (EGPS) and a 60 kV voltage 0.170 A current Acceleration Grid Power Supply (AGPS). NIO1 experiment aims at addressing several important issues to be faced in SPIDER, related to beam extraction and di agnostic optimization. Beam sources are prone to arc occurring between grids which need to be treated as normal operating condition; this means that a suitable protecti on system has to be provided. At this purpose, an electrical model based on a conceptual design of the high voltage circuit was developed to study the electrical waveform induced by the arc and identify the preliminary requirements of the protection system. The paper reports on the development of a prototype of the high voltage protection system for NIO1, for operations at reduced rated voltages: 5 kV for EGPS and 20 kV f or AGPS. Details on the design, the realization and the performance verification done w ith dedicated experimental campaigns are given. The validation of the electrical model aga inst the experimental results will be also presented and discussed.