MITICA interlock system: from prototype implementation to final system design

The construction of MITICA, the full-size prototype of the ITER Heating Neutral Beam Injectors (HNBs) is very advanced at the Neutral Beam Test Facility (NBTF) based in Padova, Italy. Some key plant systems have been delivered to the site, such as the 1 MV acceleration grid power supply system, whereas others are in the commissioning phase, such as the ion source and extraction power supply system. The integrated commissioning of the power supply system, aimed at the coordinated operation of all MITICA power supply system is scheduled for the end 2020 - early 2021. Such activity requires the coordination of the protections among the power supply systems and the management of breakdowns, short discharges between the electrostatic acceleration grids that routinely occur during MITICA operation due to the high voltage applied to grids and the short insulation gaps between grids. Since the design and construction of the MITICA Central Interlock System is a long and demanding activity, we decided to manage the power supply integration by developing an HNB provisional interlock system focused on protecting power supply systems. The design and implementation of the full MITICA Interlock system will be postponed to a later stage, when sufficient experience will be available on the management of the power supply systems and all MITICA plant systems will be ready for integrated operation. The paper will initially summarize the requirements for the MITICA Interlock in terms of architecture, ITER interlock compliance, protection instrumented functions needed, and reliability required. It will then focus on the design of the HNB provisional interlock system, discussing the redundancy requirements. It will finally propose the implementation of the provisional MITICA Central Interlock System and the final design of the full protection system.