High definition imaging in the Mega Amp Spherical Torus spherical tokamak from soft x rays to infrared (invited)

The Mega Amp Spherical Torus (MAST) diagnostic needs are strongly influenced by physics goals that often require diagnostic integration and cross-mapping, especially in fine-scale investigations, such as transport barriers. Conversely, the unrivalled viewing access to the edge, scrape-off layer (SOL) and divertor regions, provided by the MAST open geometry, impacts on the physics program priorities. A supporting suite diagnostics, such as the high definition Thomson scattering systems, provide considerable added value in detailed data interpretation (e.g., bremsstrahlung emissivity in terms of Z eff ). Thus, to exploit these advantages, an extensive set of high-resolution imaging diagnostics have been installed, encompassing soft x-rays, visible bremsstrahlung, charge exchange recognisation radiation, D α from NBI, and edge plasma neutrals, and infrared (IR) from the divertor and wall regions. Plasma light collection optics provide near parallel illumination of narrow bandpass interference filters to give monochromatic images. One adaptation provides multiwavelength images; another accommodates smooth variation of wavelength across an image (e.g., for a range of Doppler shifts beam fast neutrals). Diagnostic synergy is enhanced by combining such diagnostics to common viewing optics which allow exact-mapping. Soft x-ray tangential imaging has been achieved by using a two dimensional charge coupled device detector in a pinhole camera. Finally, a fast IR camera monitors the power deposition on the first wall and divertor plates, important in quantifying power losses (e.g., ELMs, disruptions), and complemented by visible viewing of the SOL, and linear D α cameras.