高強度サブミリ波ビームの発生とプラズマ計測への応用

概要

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Plasma scattering measurement is effective technique to observe low frequency density fluctuations (ƒ<1 MHz, k=10 cm-1) excited in plasma. The spatial and wave number resolutions and the S/N raito of measurement depend on the wavelength range, the size and the intensity of a probe beam. A well-collimated, submillimeter wave beam to offer small scattering volume and relatively large scattering angle is suitable for improving the spatial and wave number resolutions. Application of high frequency gyrotron is effective in improving the S/N raito of the measurement because of its capacity to deliver high powers. Unlike a molecular vapor laser, a gyrotron generates spreading radiation with TEmn mode structure. It is therefore necessary to convent the output radiation into a Gaussian beam (TEM00 mode), which is suitable for an effective transmission and a well-collimated probe beam. The output radiation of TE16 mode (ƒ=354 GHz, p~100 W, pulse duration 1 s) is converted into bi-Gaussian beam by a quasi-optical system consisting of a quasi-optical antenna and a focusing mirror.
福井大学の論文