Scattering theory of strongly refracting microwaves in turbulent inhomogeneous plasma. Applications of the theory to the description of fluctuation reflectometry in thermonuclear fusion devices

We present the theory of propagation and scattering of strongly refracting microwaves in turbulent inhomogeneous plasmas. We calculate the scattered signal amplitude in the case of a linear scattering regime in the Born approximation and in the case of multiple small-angle scattering. We discuss the possibility of an analytic description of multiple Bragg backscattering in a closed form. Based on the results of a theoretical analysis of microwave scattering regimes in inhomogeneous turbulent plasmas, we discuss the main fluctuation reflectometry schemes that are broadly used in toroidal thermonuclear fusion devices to analyze turbulence characteristics. We describe the methods for interpreting experimental data and the experimental approaches relying on reflectometry diagnostics that enhance the locality of measurements and their resolution with respect to the wave vectors of fluctuations.