Hannover 2016 – scientific programme

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P: Fachverband Plasmaphysik

P 26: Poster Session-Plasma Diagnostics

P 26.21: Poster

Thursday, March 3, 2016, 16:30–19:00, Empore Lichthof

Phase Contrast Imaging Diagnostic for the Wendelstein 7-X Stellarator — •Lukas-Georg Böttger and Olaf Grulke — Max Planck Institute for Plasma Physics, 17491 Greifswald, Germany

The phase contrast imaging (PCI) diagnostic allows for non-invasive measurements of density fluctuations in high temperature plasmas. Since the index of refraction in a plasma is a function of the electron density, an incoming laser beam experiences a phase shift, which can be converted to intensity variations via interference after passing a phase plate. Generally speaking, the signal contains only the line-integrated information along the beam path. This limitation can be circumvented by using the fact that the density fluctuations form filamentary structures that are well aligned with the local magnetic field. If the magnetic field direction significantly varies along the beam path, optical filtering allows for localization of the density fluctuations.

In order to identify the best diagnostic position regarding localization performance three figures of merit are introduced. They allow for quantitative comparison of different lines of sight and different magnetic field configurations. The results of the optimization process and a comparison with other fusion experiments are shown in this contribution.