The Hard X‐ray Camera on the PBX‐M tokamak (invited) (abstract)a)

The modification and control of the plasma current profile by lower hybrid current drive is considered one of the most promising avenues to control MHD instabilities and improve the high beta performance of tokamaks. The Hard X‐ray Camera on PBX‐M records images of the bremsstrahlung emitted by suprathermal electrons that carry part of the plasma current during lower hybrid current drive. The Hard X‐ray Camera is a pinhole camera that uses a 9 in. diam x‐ray intensifier as detector. It provides a tangential view of the tokamak plasma and delivers 64 images with 128×128 pixels per plasma shot. The spatial resolution in the plasma is approximately 2 cm, and the time resolution 3 ms. The camera is sensitive to x rays between 30 and 200 keV. The photon energy (and the energy of the suprathermal electrons) is measured with an absorber foil method. Modeling of the x‐ray emission has reproduced the experimental images with a better than 10% accuracy. In addition, two inversion techniques have been developed: one...