Ultrasoft X-ray diagnostics of REBEX plasma

A combined detector of ultrasoft and hard X rays was developed for the diagnostics of REB-heated plasma in the REBEX machine. The detector consists of two separate arms. In the hard-X-ray arm a scintillation detector consisting of an aluminium-covered plastic scintillator and a photomultiplier is used. The aluminium protecting foil also serves as the photocathode of a photoemission detector in the soft-X-ray arm. To enhance the detector sensitivity, the emitted photoelectrons are first accelerated and then detected by another scintillator-photomultiplier system. Two identical detectors are necessary for measurements of electron temperature using the absorber method. Electron temperatures as low as 2o to 50 eV were determined using very thin absorber foils. Time variations of plasma temperature after beam injection and during magnetoacoustic oscillations of the hot plasma column were studied. (J.U.)