Spatially Resolved Spectra of ArXVI and ArXVII from a New Type of Imaging X-Ray Crystal Spectrometer at TEXTOR-94

spherical crystals must have a large area of about 50 cm 2 and the crystal surfaces must be accurate to within 10 arc sec. In order to project a large cross-section of the plasma onto a detector, an appropriate demagnification is necessary, which is determined by the distance between crystal and detector and the distance between crystal and plasma. Since, for a high-resolution spectrometer, the distance between crystal and detector is of the order of several meters, the distance between crystal and plasma must be even larger, which in turn requires a diagnostic port of adequate height. The detector must have a large area and must be position-sensitive in two directions to provide both spectral and spatial information. Different types of detectors are presently under consideration: stacks of one-dimensionally position-sensitive multi-wire proportional counters, X-ray imaging tubes, and new large flat-panel detectors. The latter detectors are already available for medical imaging, but they have to be adapted to lower x-ray energies, which are of interest for plasma spectroscopy. Although some of these requirements are challenging, imaging x-ray crystal spectrometers offer substantial advantages over the presently used arrays of single-chord x-ray crystal spectrometers, which provide only a very limited umber of lines of sight through the plasma. The need for a cross calibration of spectra from different lines of sight is eliminated, since all the spectra are obtained by the same crystal. Compared to an array of crystal spectrometers, an imaging x-ray crystal spectrometer requires less of the precious diagnostic space and only a fraction of the installation and operating costs. Imaging crystal spectrometers have therefore been proposed for NSTX and TEXTOR-94. In this paper, we present recent experimental results from an imaging x-ray crystal spectrometer at TEXTOR-94.