Investigation of nonlinear effects in Doppler reflectometry using full-wave synthetic diagnostics

Abstract

In this work, Doppler reflectometry (DR) and radial correlation DR (RCDR) nonlinear scattering effects were studied using full-wave modeling and a set of representative FT-2 tokamak turbulences as inputs. Narrowing of the RDCR correlation function and widening of the DR poloidal wavenumber spectrum are demonstrated. An effect on the dependence of the DR signal frequency shift on the probing wavenumber is found, namely, this dependence "linearizing" in the nonlinear scattering regime. Nonlinear effects are shown to be weaker for O-mode probing than for X-mode probing, while a faster transition to nonlinear regime is demonstrated for RCDR compared to DR in both probing scenarios.