Propagation of radiation in fluctuating multiscale plasmas. I. Kinetic theory

Abstract

A theory for propagation of radiation in a large scale plasma with small scale fluctuations is developed using a kinetic description in terms of the probability distribution function of the radiation in space, time, and wavevector space. Large scale effects associated with spatial variations in the plasma density and refractive index of the plasma wave modes and small scale effects such as scattering of radiation by density clumps in fluctuating plasma, spontaneous emission, damping, and mode conversion are included in a multiscale kinetic description of the radiation. Expressions for the Stokes parameters in terms of the probability distribution function of the radiation are used to enable radiation properties such as intensity and polarization to be calculated.

Propagation of radiation in fluctuating multiscale plasmas. II. Kinetic simulations

“…18, which separate large scale propagation from small scale scattering effects and treat the latter by introducing appropriate drift and diffusion coefficients. The FTCS finite difference method is used to solve the relevant kinetic equation, for the distribution of radiation quanta in space, time, and wave vector.…”

“…18 Equation (8) can be rewritten as follows for an unmagnetized plasma (see Sec. III C of Paper I for comments on the modifications that would be necessary in the presence of significant magnetization):…”

“…[15][16][17] Direct simulation of situations like those above is impractical because of the need to simultaneously resolve fine scales while following radiation propagation over much larger distances, especially in multidimensional situations. In Paper I, 18 we formulated a kinetic description of the smallscale processes to obtain a Fokker-Planck equation for the overall large-scale evolution; similar approaches have been used by others, particularly in treating edge plasmas in fusion devices. [15][16][17] We expressed the evolution of the radiation in terms of the probability distribution function of the radiation in space, time, and wave vector.…”