Assessment of Doppler reflectometry accuracy using full-wave codes with comparison to beam-tracing and analytic expressions

Abstract

Doppler reflectometry is an established technique for measuring flows and turbulence in magnetic confinement devices using the backscatter of a probing microwave beam. However, a full understanding and quantification of the diagnostic measurement abilities and limits is missing. To address this, two-dimensional (2D) full-wave electro-magnetic and 3D beam-tracing simulations, based on realistic experimental conditions, are used to create a wide-ranging database of EM wave, spatial weighting function and instrument response model results. With the aid of wave theory and parsimonious non-linear regression techniques a set of 2D heuristic models are obtained (in terms of simple experimentally available parameters) for the principle intrinsic diagnostic sensitivities: including the wavenumber spectral mean and width of the backscattered wave, plus the spatial position and extent of the beam-turbulence interaction region. The 2D full-wave results are contrasted with (less computationally expensive) 3D beam-tracing methods to good effect.