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P: Fachverband Plasmaphysik

P 4: Helmholtz Graduate School 1 and Magnetic confinement 1

P 4.2: Vortrag

Montag, 9. März 2020, 14:30–14:55, b305

Diagnostic capabilities of X3 mode of electron cyclotron emission for electron temperature in overdense plasmas at W7-X — •Neha Chaudhary, Johan W. Oosterbeek, Matthias Hirsch, Udo Hoefel, Robert C. Wolf, and The W7-X Team — Max-Planck-Institut für Plasmaphysik, 17491 Greifswald, Germany

For magnetically confined plasmas, the lower harmonics of electron cyclotron emission (ECE) behave as a blackbody representing the electron temperature. The W7-X stellarator, for confinement reasons, is planned to work at high plasma densities aiming at detached steady state operation. For such scenarios at a magnetic field of 2.5T the ECE from the optically thick X2 mode (120-16 GHz) is in cut-off for densities more than 1.2e20/m3. Hence, electron temperature profiles cannot be accessed from ECE for over dense plasmas.

W7-X has a large aspect ratio that leads to spectrally well resolved higher harmonics of ECE compared to a tokamak with small aspect ratio. The emission from these harmonics is still present at high plasma densities and can be investigated to study plasma properties such as electron temperature and density. A Michelson interferometer was commissioned at W7-X to scan these harmonics for different plasma parameters covering broad spectral range 50-500 GHz. Initial experimental results and the radiation transport calculations (TRAVIS) suggest that X3 mode (180-220 GHz) of ECE is optically thick enough to be explored for its diagnostic capabilities as a high-density access to electron temperature. In addition, the forward modelling of experimental results is planned in the MINERVA framework.