Scattering of an electromagnetic wave in a plasma close to a cut-off layer. Application to fluctuation measurements

Abstract

The problem of wave scattering by fluctuations close to a cut-off layer is investigated. A generalized wavenumber selection rule is introduced. It provides a simple tool for analyzing the localization of scattering and defining which turbulence wavenumbers are at the origin of the observed scattered signal. Moreover, absolutely-calibrated measurements of fluctuation rates can be envisaged. Applications to four diagnostics (one- and two-antennae reflectometry, correlation reflectometry and cross-polarization scattering) are discussed.