DESIGN OF AN IMAGING BOLOMETER SYSTEM FOR THE LARGE HELICAL DEVICE

We describe a radical design for a bolometer system employing infrared (IR) imaging of a segmented-matrix absorber in a cooled-pinhole camer a geometry, which we will prototype and demonstrate on the large helic al device (LHD).(1) LHD will be operational in early 1998, with an l=2 superconducting winding, a major radius of 3.9 m, a minor radius of 0 .5-0.65 m, and input powers ranging from 3 MW (steady state) to 30 MW (pulsed). The bolometer design parameters are determined by modeling t he temperature of the foils making up the detection matrix using a two -dimensional time-dependent solution of the heat conduction equation. This design will give a steady-state bolometry capability, with modest (60 Hz) time resolution, while simultaneously providing hundreds of c hannels of spatial information. No wiring harnesses will be required, as the temperature-rise data is measured via a 12-bit, +/-0.025 degree s C resolution, 3-5 mu m band, 256x256 pixel IR camera. The spatial da ta will be used to tomographically invert the profile of the highly sh aped stellarator main plasma and divertor radiation, in conjunction wi th more conventional fanned arrays of traditional bolometers.