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P: Fachverband Plasmaphysik

P 18: Postersitzung

P 18.108: Poster

Donnerstag, 21. März 2019, 16:30–18:30, Foyer Audimax

First results from Michelson Interferometer as a broadband ECE diagnostic in W7-X — •Neha Chaudhary, Johan W. Oosterbeek, Matthias Hirsch, Udo Höfel, Robert C. Wolf, and The W7-X Team — Max-Planck-Institut für Plasmaphysik, 17491 Greifswald, Germany

For a magnetic field of 2.5T, the electron cyclotron harmonics are spectrally well separated in W7-X as it has a large aspect ratio. Because of this advantage, it is easier to measure these higher harmonics (70,140,210..GHz) compared to tokamaks with small aspect ratio. For confinement reasons, W7-X is planned to work at high plasma densities, applying O2 electron cyclotron resonance heating (ECRH). For such a plasma beyond the X2 cutoff which already has been demonstrated in the experimental campaign OP1.2a and OP1.2b of W7-X, the electron cyclotron emission (ECE) from the optically black second harmonic extraordinary mode X2 (120-160 GHz) is not present. As a result the standard ECE diagnostic consisting of a radiometer with 32 channels spread over 120-160 GHz, is not able to provide electron temperature in the regions where density exceeds the X2 cutoff value. In that case, optically grey higher harmonics provide the only access to ECE signal and hence electron temperature profiles. A Michelson interferometer was used in OP1.2b of W7-X for broadband ECE (50-500 GHz) scan. These results will be compared to modeling of ECE emission at different plasma parameters from radiation transport calculations (TRAVIS).