Bolometry systems for the TJ-II flexible heliac

Local plasma emissivity of TJ-II plasmas will be determined using pyroelect ric detectors. For tomographic reconstructions three fan-like arrays, 20 ch annels each, will be installed at the top, side, and bottom ports of the sa me sector. The designed compact in-vessel systems will use folding support structures to introduce the arrays through small diameter flanges and trans lation and rotary drives to position them at their measuring sites. Special individual "honeycomb-like" collimators (transparency of around 50% and sp atial 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 st age, radial profiles of plasma emissivity will be obtained with a single de tector, on the basis of frozen plasma parameters during a few ms. This dete ctor is equipped with a rotary slit that scans the whole plasma cross secti on from 10-20 times per shot. To perform power balances, global plasma emis sion is monitored with three pyroelectric detectors. Collimators are movabl e slits that enable probing either the full plasma cross section or narrow central chords; when fully closed they protect detectors during wall condit ioning and permit background noise characterization. (C) 1999 American Inst itute of Physics. [S0034-6748(99)52101-1].