CAMERA FOR IMAGING HARD X-RAYS FROM SUPRATHERMAL ELECTRONS DURING LOWER-HYBRID CURRENT DRIVE ON PBX-M

During lower hybrid current drive on tokamaks, suprathermal electrons are generated that emit hard x-ray bremsstrahlung. A pinhole camera has been installed on the PBX-M tokamak that records 128 X 128 pixel images of the hard x-ray plasma bremsstrahlung emitted in the 30-200 keV photon energy range. The camera has a temporal resolution of 3 ms and a spatial resolution of 3-4 cm in the plasma. The detector is a 230-mm-diam hard x-ray image intensifier. This instrument has identified hollow radiation profiles on PBX-M, indicating off-axis current drive. A detailed account of the construction of the hard x-ray camera, its operation, and its performance is given.