Electrical diagnostics for high voltage tests in MITICA.

• The insulation capability of a full silica kapton coated optical fiber in vacuum under DC voltage is about 160kV for 600mm length. • The commercial batteries providing the highest energy density for low power application are Li-SOCl2 battery • The PIC microcontroller proven to be a reliable device with respect to EMI irradiated from Surge pulses as well as it can be a very low power consumption ADC when the IDLE and Standby operational modes are exploited. • A solution to feed electronic devices operating at high voltage in harsh environments (vacuum, risk of discharges, x rays in the nearby,...) in a reliable way consists in enclosing the batteries in a vacuum tight commercial nipple closed by a dedicated feedthrough. • The precise synchronization of fast events within a system of distributed devices can be done with a distributed trigger network when a deterministic time delay is known. The trigger time can be also precisely time stamped by means of a fast transient FPGA recorder provided by a iW-RainboW-G36S board that is kept in sync with a GPS absolute time source with IEEE1588 protocol. ITER is an experimental fusion device and requires two Neutral Beam Injectors (NBIs) for plasma heating and current drive which have to supply a power of 16.5 MW each, delivered by a 1MeV deuterium beam. This D0 beam is generated starting from negative ions, produced inside a RF driven ion source, and accelerated by a Multi-Aperture Multi-Grid electrostatic accelerator insulated in vacuum. MITICA (Megavolt ITER Injector & Concept Advancement) is a full-scale prototype of the ITER Heating Neutral Beams (HNBs), devoted to test and optimize the design, under construction in Padova at the Neutral Beam Test Facility (NBTF) hosted by the Consorzio RFX. One of the most critical requirements in MITICA concerns the capability to withstand the nominal voltage of 1MV on a single long gap (≈1m), which separates the beam source and the vacuum vessel, insulated by vacuum or low pressure gas (10−6-10−3 mbar range) and with large size electrodes. In order to address this issue, a dedicated experimental test campaign exploiting a 1:1 mockup of the MITICA Beam Source will be carried out at NBTF before the installation of the actual Beam Source. During this test campaign, a set of electrical diagnostics will be installed to identify the location of the breakdowns as well as to measure the magnitude of the microdischarge currents (the precursors of vacuum breakdowns), and arc currents to provide useful information to optimize the electrostatic design of the ITER HNB and to validate the numerical models. This paper describes the development and the design of these diagnostics system based on electrical measurements. [ABSTRACT FROM AUTHOR]