Infrared Imaging Bolometer for the HL-2A Tokamak

An infrared imaging bolometer diagnostic has been upgraded recently to be adapted for the complications of the signal-to-noise ratio arising from the low level of plasma radiation and high reflectivity of low energy photon (<6.2 eV). It utilizes a platinum foil, blackened on both sides with graphite spray, as the bolometer detector. The advantage of the blackened foil is the light absorption extending into the infrared. After a careful calibration of the foil, the incident power density distribution on the foil is determined by solving the heat diffusion equation with a numerical technique. The local plasma radiated power density is reconstructed with a minimum fisher information regularization method by assuming plasma emission toroidal symmetry. Comparisons of the results and the profiles measured by an ordinary bolometric detector demonstrate that this method is good enough to provide the plasma radiated power pattern. The typical plasma radiated power density distribution before and after high mode (H-mode) transition is firstly reconstructed with the infrared imaging bolometer. Moreover, during supersonic molecular beam injection (SMBI), an enhanced radiation region is observed at the edge of the plasma.