Using a free-standing thermistor array to measure VUV emission from a tokamak plasma

A compact 15-channel bolometer array composed of discrete thermistors has been installed on the Princeton Beta Experiment tokamak. The response time, fastest for detectors with low thermal capacities, has been optimized by using ‘‘free-standing’’ detectors. The detector is supported only by thin electrical leads and no thermal substrate is employed. Overheating due to limited heat dissipation is controlled with careful detector biasing. The sensitivity is limited by the systematic errors in the model of the heat transfer from the detector to the electrodes and leads. A two-pole cooling model was found to characterize the detector’s thermal decay far better than a simple exponential and resulted in an NEP≊3×10−7 W/√Hz with a 300-Hz bandwidth.