Development of a prototype infrared imaging bolometer for NSTX-U

Measurements of the radiated power in fusion reactors are of high importance for studying detachment and the overall power balance. A prototype Infrared Video Bolometer (IRVB) is being developed for NSTX-U complementing resistive bolometer and AXUV diode diagnostics. The IRVB has proven to be a powerful tool on LHD and JT-60U for its 2D imaging quality and reactor environment compatibility. For NSTX-U, a poloidal view of the lower center stack and lower divertor are envisaged for the 2016 run campaign. The IRVB concept images radiation from the plasma onto a 2.5 $\mu $m thick 9 x 7 cm$^{\mathrm{2\thinspace }}$calibrated Pt foil and monitors its temperature evolution using an IR camera (SB focal plane, 2-12 $\mu $m, 128x128 pixels, 1.6 kHz). The power incident on the foil is calculated by solving the 2D$+$time heat diffusion equation. Benchtop characterization is presented, demonstrating a sensitivity of approximately 20 mK and a noise equivalent power density of 71.5 $\mu $W cm$^{\mathrm{-2}}$ for 4x20 bolometer super-pixels and a 50 Hz time response. The hardware design, optimization of camera and detector settings as well as first results of both synthetic and experimental origin are discussed.