Optical diagnostics for high voltage tests in MITICA

The Neutral Beam Test Facility (NBTF, Padova, Italy) is a facility devoted to the test and optimization of the Neautral Beam Injector for ITER. A full-scale prototype, called MITICA, is under construction at NBTF and has to demonstrate all the design parameters for ITER, among which a stable beam operation at the enrgy of 1MeV. In order to test and optimize the stable high voltage holding of 1MV, a dedicated campaign is foreseen for 2022, utilizing realistic mock-ups of MITICA ion source and accelerator. During the campaign, the mock-up of the ion source will be biased with an increasing potential up to -1MV and the discharge towards the grounded electrodes will be observed. In this way, possible weak points of the geometry will be detected and possibly mitigated. As diagnostics for discharge position and intensity, a system of cameras was designed, including visible cameras, IR camera and fast camera. The results of this optical diagnostics will be then compared with the electric measuments of the discharges taken on a dedicated ground electrode, for a cross check. This paper describes the motivations of the choice of the type and number of diagnostic cameras adopted during the experiments, the optimization of their layout, which includes also the use of a series of mirrors, the design of supports and protection systems, and the procedure to interpret the experimental data and cross check them with the electric measurements.