Spatial and wavenumber resolution of Doppler reflectometry

Doppler reflectometry spatial and wavenumber resolution is analysed within the framework of the linear Born approximation in the slab plasma model. An explicit expression for its signal backscattering (BS) spectrum is obtained in terms of the wavenumber and frequency spectra of turbulence, which is assumed to be radially statistically inhomogeneous. The scattering efficiency for both back (BS) and forward scattering (FS) (in the radial direction) is introduced and shown to be inversely proportional to the square of the radial wavenumber of the probing wave at the fluctuation location, thus making the spatial resolution of diagnostics sensitive to the density profile. It is shown that in the case of FS additional localization can be provided by the antenna diagram. It is demonstrated that in the case of BS the spatial resolution can be better if the turbulence spectrum at high radial wavenumbers is suppressed. The improvement in Doppler reflectometry data localization by a probing beam focusing on the cut-off is proposed and described. It is shown that Doppler reflectometry data interpretation based on the obtained expressions is possible.