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Author(s):
P.C. de Vries, Y. Nagayama, K. Kawahata, S. Inagaki, H. Sasao and K. Nagasaki
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Title:
Polarization of Electron Cyclotron Emission Spectra in LHD
Date of publication:
July 1999
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Key words:
ECE emission, Mode conversion, Diagnostics
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Abstract:
Electron cyclotron emission (ECE) can be used to determine the electron temperature proflle in magnetized plasmas. The complex structure of the magnetic fleld configuration in the Large Helical Device (LHD), which has a large shear, complicates the analysis of the ECE spectrum. In a sheared magnetic field the propagation of X and O-mode polarization through the plasma are coupled, causing mode conversion and polarization rotation. Mode scrambling is also caused by wall reflections. In this report, this mode conversion in LHD is numcrically analyzed. It was found that at low density mode conversion scrambles the ECE spectra. However, at higher density (n_eo > 1.0 10^19 m^-3) the polarization mode is found to rotate with the sheared magnetic fileld, yielding only a negligible mode conversion. Wall reflections are found to depolarize the ECE spectrum. Notwithstanding the LHD magnetic configuration, it is shown that temperature profiles could be revealed from the ECE spectra.
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