Transition into diffusive regime of propagation of probing electromagnetic waves in a turburlent inhomogeneous plasma and limitations for microwave reflectometry in reactor scale devices

A propagation of probing waves in plasma in the presence of broad wavenumber spectrum density turbulence is examined in one-dimensional geometry in this paper. It is shown that multiple Bragg scattering leads to a transition into diffusive regime of the wave propagation obstructing the plasma density profile measurement, if the turbulence level exceeds a threshold value. The criteria determining the threshold plasma density fluctuation level are derived both in the one-dimensional model and accounting for the two-dimensional side-scattering effects. The corresponding thresholds are evaluated for different modifications of reflectometry diagnostics planed for ITER.