Derivation of bolometer equations relevant to operation in fusion experiments

An overview of the bolometer diagnostic in the W7-AS stellarator is presented. Bolometers are used in plasma physics to measure radiated power losses that are mainly produced by impurity lines and neutral particles. With an array of collimated bolometers, the spatial and temporal evolution of these losses can be measured. The accuracy of the inversion of the line integrated measurements into local values necessitates a careful calibration and conversion of the measured signal into an incident power of each foil. Using transmission line theory to determine the equivalent circuit for the sensor and cable, the equations for bolometer calibration and measurement, taking into account the cable resistance and capacitance between amplifier and detector, are derived. The ability to switch the bolometer amplifiers from measurement to calibration mode between discharges allows continuous monitoring of the calibration constants of the bolometer foil. Measurements by bolometer cameras and their Abel inversion for the radial profile of radiated power in W7-AS are presented. (C) 2002 American Institute of Physics