Radiated power diagnostic capabilities on MAST Upgrade

Capabilities to measure radiated power on MAST Upgrade are discussed. A new 32-channel resistive bolometer (RB) system is used in the device’s unique Super-X divertor (SXD) chamber, complemented by the 32-channel system originally used on MAST, viewing the core plasma. Both utilise modern FPGA-based electronics, and the resulting improvements in signal-to-noise ratio and signal processing capabilities are summarized.

Example tomographic reconstructions of the emissivity have been calculated using volumetric ray tracing methods. Inversions on a range of phantoms, both in the SXD and the core, indicate expected performance of the RB diagnostics for different plasma radiation scenarios. Metrics such as the total radiated power and the mean position of radiation are reproduced with good accuracy (within 10% of the phantoms) for most radiation profiles, but inversions are poor for highly elongated phantoms and phantoms peaked close to the walls in certain regions of the SXD chamber.

A prototype infra-red video bolometer (IRVB) is being used to overcome limited RB coverage of the x-point regions. It will provide high spatial resolution, 2D radiation profiles for the lower x-point region. IRVB design and bench-top calibration results are presented along with initial signal modelling.