Optical Diagnostics for High-Voltage Tests in MITICA

The Neutral Beam Test Facility (NBTF), Padua, Italy, is a facility devoted to the test and optimization of the Neutral Beam (NB) 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 energy of 1 MeV. To test and optimize the stable high voltage holding of 1 MV, a dedicated campaign is foreseen for 2022–2023, utilizing realistic mockups of MITICA ion source and accelerator. During the campaign, the mockup of the ion source will be biased with an increasing potential up to $-$ 1 MV and the discharge toward the grounded electrodes will be observed. In this way, possible weak points of the geometry will be detected and possibly mitigated. As diagnostics for arc discharge position and intensity, a system of cameras was designed, including visible cameras, high-speed camera, and IR camera, placed on the available viewports of beam source vessel, and pointed toward the areas with higher probability of electric discharge. The results of this optical diagnostics will be then compared with the electric measurements of the discharges taken on a dedicated ground electrode, for a cross check. This article 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 mirrors, and the design of mechanical supports.