X-ray diagnostics on WENDELSTEIN 7-AS

The spatially and temporally resolved x-ray emission in the W7-AS stellarator is analyzed by three diagnostic systems. The first consists of two cameras using arrays of surface barrier diodes. A variety of absorber-foils can be used to change the spectral response of the system. This flexibility allows one to analyze impurities and magnetohydrodynamic (MHD) activity. The measurements are also used for the reconstruction of equilibrium parameters (e.g., Shafranov shift) and of the topology of MHD modes. The second system serves to monitor the electron temperature profile by using the two-foil method. Pairs of large ion-implanted Si diodes in combination with different foil combinations are used. In addition, the measurements provide routine informations about Zeff, plasma position and profile width. Finally, a compact camera system (ten cameras with planar pin-diode arrays and curved Be-foils, 320 viewing chords) inside the vacuum vessel allows one to obtain proper two-dimensional tomograms of the equilibr...