Electron Cyclotron Emission Measurements by Means of a Grating polychromator on the large Helical Device

摘要

The electron cyclotron emission (ECE) spectrum at the Large Helical Device (LHD) is measured yb a 14-channel grating polychromator. During standard operation the polychromator monitors 2~nd harmonic frequencies (100 - 150 GHz) with a spectral resolution of 1.5 GHz. At sufficient high density the 2~nd harmonic X-mode polarisation is optically thick and can be used to determine the temperature profile. However, the large magnetic field shear in LHD affects the ECE polarisation. This effect has been studied numerically. The wave polarisation was found to rotate in the laboratory frame. Experiments have been carried out by means of a polarisation rotator in the diagnostic waveguide system, which confirmed the calculations. By a proper setting of the poalrisation rotator, the rotation can be corrected and pure X-mode is detected. Temperature profiles have been measured successfully by the polychromator.