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 (L(r(phi))) and from power fluctuations (L(r(P))) show variations with the poloidal k-spectral width, the surface fluctuation amplitudes (weak and strong turbulence) and the microwave beam width. L(r(P)) is always smaller than the true correlation length L(r(true)) (computed from the layer fluctuations) by a factor of root 2 to 2 depending only on the fluctuation amplitude. L(r(phi)), however, is much larger than L(r(true)) for weak fluctuations and drops with increasing fluctuation amplitude to less than L(r(true)). L(r(phi)) also varies with the beam width and poloidal k-spectra, while L(r(P)) does not. A relationship, involving the rms phase fluctuation level, is found between L(r(phi)) and the true correlation length.