Overview of ECE diagnostics on LHD

An electron cyclotron emission (ECE) diagnostic system has been installed on the large helical device (LHD). In LHD, the magnetic field profile has a peak near the plasma center, so the electron temperature profile of both sides can be continuously measured by the ECE system using two antennas. The ECE spectrometers are as follows, two heterodyne radiometers with the local frequency of 70 and 132 GHz, respectively, a grating polychromator and a Michelson spectrometer. The measurements are processed by the distributed data acquisition system. The angle of the magnetic field from the toroidal direction varies from −30 to +30° in LHD. It is found that the polarization of ECE follows the angle of the magnetic field when the electron density is high enough. The effect of the polarization is considered when the temperature calibration is performed. ECE is useful to distinguish small perturbations in the electron temperature profile, for example, to effects of a local island diverter.