Bolometry systems for the TJ-II flexible heliac

Local plasma emissivity of TJ-II plasmas will be determined using pyroelectric detectors. For tomographic reconstructions three fan-like arrays, 20 channels each, will be installed at the top, side, and bottom ports of the same sector. The designed compact in-vessel systems will use folding support structures to introduce the arrays through small diameter flanges and translation and rotary drives to position them at their measuring sites. Special individual "honeycomb-like" collimators (transparency of around 50% and spatial resolution of about 2 cm at the plasma center) have been designed to optimize the signal level and to act as a microwave filter. In the first stage, radial profiles of plasma emissivity will be obtained with a single detector, on the basis of frozen plasma parameters during a few ms. This detector is equipped with a rotary slit that scans the whole plasma cross section from 10-20 times per shot. To perform power balances, global plasma emission is monitored with three pyroelectric detectors. Collimators are movable slits that enable probing either the full plasma cross section or narrow central chords; when fully closed they protect detectors during wall conditioning and permit background noise characterization. (C) 1999 American Institute of Physics. [S0034-6748(99)52101-1].