Operation of multi-channel tangential bolometer on PBX

This paper discusses compact 15-channel bolometer array that views plasma emission tangentially across the mid-plane that has been installed on the PBX tokamak. By comparing these diagnostics, poloidal asymmetries in the emission profile can be determined. The detector array consists of 15 discrete 2 mm diameter thinistors, a sintered metal-oxide, which has a high temperature coefficient. Each active detector is operated in tandem with an identical blind detector in a constant current DC Wheatstone bridge configuration. The variation in bias voltage is amplified and stored on a CAMAC transient recorder. The detectors are sensitive to accumulated heat and software has been written to smooth and differentiate the signals so that instantaneous power can be calculated. The cooling time constants are determined (3.1 seconds) so that the loss of heat from the detector during the course of a shot can be compensated. The detectors were relatively calibrated with a tungsten-halogen filament lamp and were found be vary by ±7%. The irradiance profiles are inverted, and the emissivity is typically in the 0.1 to 0.5 W/cm3 range