Collective scattering from plasmas: effects of particle and fluid motions

Electromagnetic wave scattering is a classical diagnostic tool for both fusion and space plasmas. As it is well known, there exist two scattering conditions: incoherent fluctuations, which are the manifestation at small scales of the plasma discrete structure and which are produced by the random motion of individual independent particles, and collective fluctuations at large scales, associated with the scattering determined by dressed particles. The scattering spectrum depends upon thermal particle motion, and the plasma temperature governs the shape of the spectral distribution of the scattered radiation over the frequency. Meanwhile, for the conditions of some experiments, for instance tokamak microwave or infrared scattering experiments, or magnetospheric radar backscattering experiments, the scattering factor can be substantially modified due to macroscopic fluid-like flows in the plasma. The latter can appear as a result of low-frequency and large-scale electromagnetic fields, produced either by some external sources or internal factors, in particular MHD turbulence. In this paper the effect of fluid-like plasma motion on the electromagnetic wave scattering from magnetized plasma is studied. It is suggested, that such motion perturbs the clouds of polarization charge around particles. This phenomenon of renormalized screening determines the collective scattering spectrum from the magnetized kinetically stable but MHD agitated plasma. (author) 4 refs., 2 figs