A shinethrough detector and interlock for neutral beam injection operations on MAST-U

• NBI shinethrough has the potential to damage plasma facing components. • An infrared detector is used to detect shinethrough from neutral beam dump. • The detector signal can be used as an interlock to avoid excessive temperatures. • The effect of dust on beam dump tiles on the measured signal is considered. Neutral Beam Injection (NBI) is a powerful tool and is very commonly used for heating, current drive and diagnostics on magnetically confined devices for fusion power development. Not all the neutral beam power is deposited within the plasma. This shinethrough power must be dealt with at the first wall and any components irradiated by it must be protected against excessive heating. This paper describes the design, implementation and testing of a shinethrough detector and interlock for the MAST-U machine. It is based on the detection of the infra-red emission from the beam dump which can then be used to terminate the beam pulse if this exceeds a required threshold. The effects on the detected signal of loosely bound material (“dust”) on the beam dump is also discussed.