MULTICHORD CALIBRATED BOLOMETER ARRAY FOR THE RFX EXPERIMENT

A new multichord bolometer array has been installed for the first time in the RFX experiment, a large machine designed to study plasma confinement at high current in the reversed field pinch configuration. The main purpose of the diagnostic is to provide emissivity spatial profiles with good time resolution for the measurement of the total radiated power. The detectors used are miniaturized metal foil bolometers which are mounted in a water cooled pinhole camera covered by a graphite shield. The bolometers can be absolutely calibrated in situ according to a technique originally developed for the Asdex tokamak. In order to prove the electrical calibration technique a blackened bolometer was optically irradiated with a monochromatic light over a wide spectral range with wave numbers from 2.7 up to 47 000 cm-1. In the visible and UV spectral range an absorptivity of 80% was measured while in the IR and far-infrared regions only 7% of the incoming light was absorbed by the bolometer foil. In the mm wavelength range less than 1% of the radiation was absorbed.