A millimeter-wave phase-imaging interferometer has been developed for the study of density profiles of the GAMMA 10 tandem mirror. The interferometer uses a 70-GHz klystron oscillator and a quasi-optical transmission system. The probe beam is expanded so as to fill an orthogonal view of a plasma cross section. The view is imaged onto a detector array. The detector array consists of beam-lead GaAs Schottky barrier diodes bonded to antennas fabricated using photolithographic techniques on a fused-quartz substrate. Two types of antennas, bow-tie and Yagi-Uda antennas have been used in order to provide an effective matching to millimeter-wave beams, and compared for the performance of an imaging system. The interferometers have been applied to the central-cell and plug-cell plasmas of GAMMA 10.

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A ten-element imaging array which consists of an integrated antennadetector system that incorporates traploaded Yagi antennas and Schottky diodes has been developed for operation in the millimeter-wave band around 70 GHz. Also, a prototype optical system that comprises a millimeter-wave phase-imaging interferometer has been designed and fabricated. They were fitted to the GAMMA 10 tandem mirror at Tsukuba University. A real-time measurement of the radial distribution of the plasma electron density was successfully demonstrated using those systems.

A millimeter-wave imaging array is proposed in which many Yagi-Uda antennas are placed on a dielectric lens. By changing the dimensiions of these antennas, the impedance matching with the detector is optimized. At the same time, a radiation pattern matched to the incident beam from the fwusing optics is realized. The crosstalk between the adjacent detectors on the array is measured. An optimum spacing is derived and a good imaging property is realized. The present irnaging array is suitable for MMIC and is applied in practice for plasma measurement for nuclear fusion research.

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