High definition imaging in the Mega Amp Spherical Tokamak

An absolutely calibrated, visible imaging diagnostic has been deployed on the MAST spherical tokamak. Two sets of three-color channels are defined using a combination of stacked multi-cavity interference filters, color-glass filter, and a color-pixel sensor. The system is compact with a single viewing pupil, which facilitates unambiguous comparisons of measurements in 2D. The sensor has a 12-bit dynamic range, 50 μs to 10 ms integration time (with 100-200 Hz frame rate), and a wide field of view with 640 × 480 resolution. The center-wavelength and the spectral bandpass for all colors are maintained across the field of view as they are controlled in the optical telecentric domain. The design views a complete plasma cross section, which contains passive plasma-edge and active interior emissions: one of the two neutral beam emissions, plasma-impurity charge-exchange emissions from both equator neutral beams, and two colors of bremsstrahlung.