Observation of Electron Density Fluctuations by Using the O-Mode Microwave Imaging Reflectometry (O-MIR) in LHD

Abstract

The O-mode microwave imaging reflectometry (O-MIR) has been developed. The frequency is 26 - 34 GHz,which corresponds to the cutoff electron density of 0.8 - 1.5 × 10¹⁹ m⁻³. Since the local wave of the newly developed horn antenna millimeter wave imaging device (HMID) is fed by coaxial cable, the optical system of O-MIR is significantly simplified. By using O-MIR, the edge electron density fluctuation in an H-mode plasma is observed in LHD. The spectrum in the wave number and the frequency (k - ω) space is obtained by using the two-point correlation analysis. In the H-mode plasma the fluctuation amplitude is higher and the k - ω spectrum has the feature of the drift wave.