Plans for two-dimensional steady state bolometric measurements of the large helical device

Preliminary plans for two-dimensional steady state bolometric measurements of core plasma and divertor regions have been made for the Large Helical Device (LHD) under construction at the National Institute for Fusion Science. Using a semi-tangential plane through the plasma volume, a two-dimensional view of the core plasma is achieved from the outboard, upper and lower diagnostic ports. Divertor regions will also be viewed from the upper, lower and outboard ports. In the case of divertor and core plasma arrays, duplicate detector arrays will alternate in turn between viewing and active cooling phases, using fast shutters to enable continuous detection during long-pulse (30 min) operation of the LHD. Each detector array will consist of 32 metal film bolometers and 64 XUV photodiode arrays, resulting in a spatial resolution of about 2–4 cm. The temporal resolution should be about 1 ms for the film bolometers and 1 μs for the photodiodes. Additional arrays will include a one-dimensional array that views from an outboard port, and an array of toroidally spaced detectors for investigating the toroidal variation of the radiated power. During the present stage of development, various detector samples are being acquired and tested. Schematics of the bolometer arrays, as well as plans for the complete bolometer diagnostic system will be shown.