Design of the off-axis neutron camera for the Mega Ampere Spherical Tokamak (MAST) Upgrade

A dedicated four-channel, collimated neutron flux monitor has been designed for the Mega Ampere Spherical Tokamak (MAST) Upgrade to measure spatially resolved neutron emissivity in the off-axis Neutral Beam Injection (NBI) region, contributing to studies of fast-ion confinement and the effectiveness of plasma heating and current drive. This paper presents the design and motivation for the off-axis neutron camera (OANC) for MAST Upgrade. It describes the line-of-sight geometry, detection system, shielding configuration, and laboratory characterization of detectors using γ-ray sources. The OANC is optimized to complement the existing on-axis Neutron Camera Upgrade diagnostics and provide measurements in previously inaccessible regions. The design achieves 10% statistical accuracy with 10 ms time resolution in off-axis NBI scenarios. The diagnostic will be installed during the next engineering break and will become operational in the following campaign. The off-axis neutron camera is expected to provide valuable insights into fast-ion deposition, plasma heating, and confinement driven by off-axis NBI.