Improvement in the performance of plasma scattering measurement by applying the high power submillimeter radiation source (Gyrotron)

Density fluctuations in magnetically confined plasmas are important physical quantities to be measured for the basic study of plasma confinement, aince the density fluctuations are theoretically expected to enhance the energy loss of the confined plasma across the magnetic field. The scattering method with electromagnetic wave makes it possible to observe frequency and wavenumber of the fluctuations directly with a high spatial and wavenumber of the fluctuations directly with a high spatial resolution. The performance of plasma scattering measurement (S/N ratio, the spatial and wave number resolutions) depends on intensity, wavelength range and quality of a probe beam. A submillimeter wavelength range and quality of a probe beam. A submillimeter wavelength beam is the most suitable for improving both the spatial and the wave number resolutions. Application of high frequency gyrotron is effective in improving the S/N ratio of the measurement because of its capacity to deliver high powers. In order to meet the high requirements need for measurement, the output radiation of the gyrotron FU Ⅳ has been stabilized by introducing a smoothing circuit in the high-voltage power supply. In addition, conversion of the output radiation into a Gaussian beam ‘TEM00 mode) is necessary for an effective transmission and irradiation of the plasma by a well-collimated probe beam