Design of NBI Protection Plates of JT-60SA

This article introduced design work of NBI Protection Plates (NPP) of JT-60SA. The neutral beam is partially re-ionized by collision with environmental gas molecules, and the ionized beam is bended by the magnetic field, resulting in heat flux on the wall of the NBI duct, which includes NBI gate valve, NBI side bellows, port extension, vacuum vessel (VV) side bellows and port. The heat flux is estimated to be 0.5-3MW/m2 in the port and 0.2MW/m2 in the other areas, and its duration is 100s. Considering the long-pulse high heat flux, NPP was installed in the NBI duct as a water-cooled thinner duct. Three types of NPP were designed for three types of NBI in the JT-60SA, i.e., perpendicular NBI (P-NBI), tangential NBI (T-NBI) and negative-ion NBI (N-NBI). The NBI duct was separated into three parts connected loosely with each other by two bellows. The designed NPP was separated into two or three parts along the beam line, which were overwrapped securing a sufficient gap considering the relative displacement with each other. The protection plates in the port area were designed as sets of narrow (~15cm) and long (~2m) cooling plates surrounding the neutral beam, to reduce the electro-magnetic force due to eddy current at the moment of the plasma disruption. The protection plates in other area were designed as sets of conical or columnar copper plates bonded to cooling pipes considering low magnetic field. Even the space in the NBI duct was very limited, the inner diameter of NPP was designed to be sufficiently large not to scrape the neutral beam. Considering heat loads from the neutral and re-ionized beam, electro-magnetic force due to eddy current and acceleration due to earthquake and disruption, numerical analyses were carried out and it was confirmed the design of the NPP was reasonable.
31st Symposium on Fusion Technology (SOFT2020)