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Argon photoion spectra have been obtained for the first time in coincidence with K-LL and K-LM Auger electrons, as a function of photon energy. The simplified charge distributions which result exhibit a much more pronounced photon-energy dependence than do the more complicated noncoincident spectra. In the near-AT-threshold region, Rydberg shakeoff of np levels, populated by resonant excitation of K electrons, occurs with significant probability, as do double-Auger processes and recapture of the K photoelectron through postcollision interaction.

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A pulse height analysis (PHA) system has been designed and manufactured for the Wendelstein 7-X stellarator, in such a way as to be already compatible with later quasi-continuous operation requirements. The diagnostic will provide X-ray spectra with energy resolution better than 180 eV. The system has three energy channels: 0.25-20 keV, 0.95-20 keV and 1.5-20 keV. For each channel a separate Silicon Drift Detector (SDD) equipped with a suitably selected beryllium foil is used. The range of the 3 energy channels can be further adapted to particular experiments by moving via a pneumatic actuator additional beryllium filters in front of the fixed ones. The PHA system is intended for measuring impurity species (e.g. C, Fe, Ni), electron temperature and for investigating possible suprathermal tails in the spectra. The system will be installed on the horizontal port AEK50 on W7-X. The SDD detectors, the replaceable filters and the adjustable piezo driven slits which allow to suitably adapt the X-ray signal intensity are mounted inside a vacuum chamber which is connected to the plasma vessel via a gate valve. The on-air diagnostic components are the preamplifiers, the Digital X-Ray Processor (XIA, U.S.A.), a computer, and an X-ray calibration source. For controlling the operation of the entire diagnostic system, as well as, for the data acquisition of the electrical pulses coming a special code was developed. The paper presents the construction of the PHA system for W7-X and the laboratory tests of its mechanical parts together with the information on the code developed to operate the diagnostic. The diagnostic was also tested and characterised by measuring Fe55 spectrum and fluorescence spectra of Ni, Fe, Cr and Cu induced by an X-ray mini-tube.