Fusion Science and Technology / Volume 58 / Number 1 / July/August 2010 / Pages 412-417
Chapter 8. Diagnostics / Special Issue on Large Helical Device (LHD)
Bolometers are a powerful tool for diagnosing plasma radiation in a reactor-relevant environment. Resistive and imaging bolometers have been applied to the Large Helical Device (LHD) to measure radiative phenomena. Installed on LHD are 56 channels of resistive bolometers at four different ports, providing total radiated power measurements and radial profiles with 5-ms temporal resolution. Calibration coefficients are seen to vary slightly year to year. Imaging bolometer foils are installed at four ports. Infrared cameras have been used at some of these ports to provide an image of the foil temperature, which can be analyzed to give an image of the radiated power absorbed by the foil. Upgrades of existing imaging bolometers using platinum foils and more advanced infrared cameras with frame rates of 345 and 420 frames/s (minimum time resolutions of 3 and 2.5 s, respectively) are introduced. Variations of the thermal parameters on thin platinum (2.5-m) foils are measured in a calibration experiment. The thermal properties of the foil can be quantified experimentally by measuring the responses of the foil temperature in the form of the peak change in temperature and thermal time (average of thermal decay and rise times) to a chopped HeNe laser. These measurements are made in 1-cm increments moving in two dimensions across the foil or at 63 separate locations. The imaging bolometers are intended to give images of complex three-dimensional radiative phenomena and ultimately provide the data for one-, two-, and three-dimensional tomographic inversions.