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P: Fachverband Plasmaphysik
P 6: Helmholtz Graduate School I
P 6.8: Poster
Montag, 13. März 2017, 16:30–18:30, HS Foyer
A Phase Contrast Imaging Diagnostic for Turbulence Measurements in the Wendelstein 7-X Stellarator — •Lukas-Georg Böttger1,2, Olaf Grulke1, and Eric Matthias Edlund3 — 1Max-Planck Institute for Plasma Physics, 17491 Greifswald, Germany — 2Technical University of Denmark, 2800 Kgs. Lyngby, Denmark — 3Massachusetts Institute of Technology, Cambridge, MA, USA
The phase contrast imaging (PCI) diagnostic allows for a non-invasive imaging of electron 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 by utilising a phase plate. Initially, the image contains only the line-integrated information along the beam path. However, if the magnetic field direction significantly varies along the beam path, a spatial resolution can be obtained by optical filtering.
The diagnostic is designed to operate in the range from large scale ion temperature gradient (ITG) to smaller scale trapped electron mode (TEM) and electron temperature gradient (ETG) turbulence. Simulations for ITG and TEM turbulence in W7-X geometry were performed (e.g. Helander et al., Nucl. Fusion 55 (2015) 053030) and show, inter alia, much more poloidally localised turbulent structures than in Tokamaks. Hence, the specific diagnostic location strongly influences the observations. Based on the simulations we discuss possible measurement results as a preparation for the upcoming operation phase OP 1.2 and give an update of the diagnostic design and testing process.