Development of imaging bolometers for long-pulse MFE experiments (invited)

We have developed the concept of an imaging bolometer, capable of operation with 100's of individual channels, while relying on optical (infrared) rea dout of the temperature rise in a thin foil. A thin gold foil (0.5-5 mu m t hick) is sandwiched between pieces of copper. The copper mask (a large ther mal mass) has a hole pattern drilled into it to form many "individual pixel s," effectively forming many separate sensors. This segmented foil/mask com bination is exposed on its front side to plasma radiation through a cooled pinhole camera geometry. Simultaneously, a high-resolution infrared camera monitors any temperature change on the backside of the thin foil. A sensiti ve infrared (IR) camera views the foil through an IR telescope/periscope sy stem, and is shielded from the magnetic and nuclear radiation fields, eithe r by distance and/or material shielding. A simple time-dependent design alg orithm, using 1D heat transport to a cold boundary, has been written in Mat hCad, which allows us to select optimal material and geometries to match th e expected plasma conditions. We have built a compact prototype with 149 ch annels, and tested it successfully both in a vacuum test stand in the labor atory, and on a plasma in the CHS at the National Institute for Fusion Scie nce, subjecting it to electron cyclotron heated and neutral beam injection heated conditions. A water-cooled version has been built for the new LHD. S ince the IR imaging bolometer uses only metal parts near the plasma, and ha s no need for wiring or wiring feedthrus, it is intrinsically radiation har d, and has direct application to ignition device to test engineering concep ts (ITER), or ITER-class experiments. (C) 1999 American Institute of Physic s. [S0034-6748(99)66101- 9].