Concepts of x-ray diagnostics for WENDELSTEIN 7-X

The use of superconducting coils in W7-X will allow to run very long pulses (up to 30 min). Therefore enhanced demands have to be met for plasma diagnostics with respect to hardware components exposed to steady state heat fluxes, but also to the data acquisition and analysis. A multicamera x-ray tomography system inside the vacuum vessel--because of lack of suitable ports--with about 400 viewing chords distributed along the poloidal direction is proposed for magneto hydrodynamics investigations. The system will consist of about 20 compact cameras containing linear photodiode arrays, beryllium-transmission foils, and preamplifiers. A particular technical issue is the control of detector/amplifier offset and gains in steady state plasmas. Another multipurpose x-ray camera system with interchangeable filters will be installed using a particular port combination. In addition x-ray pulse height analysis will be used to deduce spectroscopic information and to provide the central electron temperature