A low noise highly integrated bolometer array for absolute measurement of VUV and soft x radiation

A new low noise miniaturized multichannel bolometer module for absolute measurements in the VUV and soft x spectral ranges is described. Highly integrated four-channel modules (2×3.3×1.5 cm3) each comprising four independent ac-excited (50 kHz) metal resistor bolometer bridges were successfully tested on a large tokamak (Tore Supra in Cadarache) and on an electron synchrotron (BESSY in Berlin). The bolometer system features a linear response to the absorbed radiation power, a low detection limit (≤1.0×10−6 W cm−2 on Tore Supra with an integration time of τint=10×10−3 s) and a low NEP (≤10×10−9 W on BESSY). The thermal cross-talk between adjacent detectors is negligible (0.003) and a low thermal drift ΔUBr/ΔT 10−4 V °C−1 is achieved. It can be operated at a maximum temperature of 150 °C, at high magnetic fields (tested up to B=4.5 T in the laboratory) and survives high nuclear radiation doses. The system offers the possibility of detecting low-power VUV and soft x-radiation with sampling rates of up to 10 kHz on plasma machines and of absolutely calibrating VUV and soft x instruments. Effective suppression of electric, thermal and nuclear radiation interferences is characteristic of the bolometer system.Strain gauge effects, which could affect the behavior of the bolometers at high magnetic fields, are suppressed by the ac-excitation technique.