A two-dimensional full-wave numerical code in the extraordinary mode of propagation has been developed to simulate reflectometry. The code uses the finite-difference time-domain technique to solve wave propagation in magnetized and turbulent plasmas. The code has been used to study the viability of the Doppler reflectometry technique in determining the perpendicular rotation velocity of density fluctuations. The influence of parameters like plasma curvature, probing beam characteristics, turbulence wave-number spectral width and antenna tilt angle is studied. Accurate Doppler measurements can be obtained using Gaussian beams with low divergence and optimum beam waist in slab plasmas and also in plasmas with high curvature. Gaussian beam antennas with optimum spot size provide accurate Doppler frequency values for a wide range of wave-number spectral widths of the turbulence. Doppler measurements at large tilt angles—high probed wave-numbers—are able to give accurate results on the Doppler frequency keeping the enhancement factor of the probing electric field close to the cutoff layer and therefore its contribution to the spatial localization of the measurement; however, the efficiency of the Bragg backscattering process—defined as the ratio between the backscattered and incident power—is low at large tilt angles.
Fluctuation spectra and velocity profile from Doppler backscattering on Tore Supra