2D modelling of radial correlation reflectometry

The response of a radial correlation reflectometer to turbulent plasma fluctuations in a tokamak/stellarator is studied using a two-dimensional (2D) physical optics/distorted surface model. Reflectometer phase and power time signals are generated numerically using the Helmholtz equation and simulated reflection layers. The layers are linked by a radial (wavenumber) k-spectrum with a common poloidal/transverse k-spectrum and a linear dispersion relation. The radial correlation lengths computed from phase fluctuations and from power fluctuations show variations with the poloidal k-spectral width, the surface fluctuation amplitudes (weak and strong turbulence) and the microwave beam width. is always smaller than the true correlation length (computed from the layer fluctuations) by a factor of to 2 depending only on the fluctuation amplitude. , however, is much larger than for weak fluctuations and drops with increasing fluctuation amplitude to less than also varies with the beam width and poloidal k-spectra, while does not. A relationship, involving the rms phase fluctuation level, is found between and the true correlation length.