Development of microwave imaging diagnostics in LHD

The microwave imaging reflectometer (MIR) and the electron-cyclotron-emission imager (ECEI) have been developed to diagnose the LHD plasma and have succeeded, for the first time, in obtaining three-dimensional MIR images. As their elements, the microwave imaging optics, the multi-frequency microwave oscillator, the two-dimensional horn antenna array (HMA) with mixer and the on-board frequency-separation and detection circuits have newly been developed. In MIR, the microwave with four frequencies was irradiated onto plasma and the reflected wave and the local oscillator wave were imaged on the two-dimensional HMA. Amplitude and phase signals were obtained from the IF signal after separation of four frequency components. In ECEI, the electron cyclotron emission (ECE) and the local oscillator wave were imaged on the one-dimensional HMA with the 93 GHz high-pass filter plate to generate the IF signal. The ECE power in the frequency range 97-104 GHz was measured from the IF signal through a newly developed 8-channel frequency separation circuit. Using these systems in preliminary experiments of LHD, authors successfully observed a three-dimensional mode structure localized at the plasma edge. This result demonstrates that the microwave imaging is quite useful tool for measuring local disturbances in the plasma. (T.I.)