Three-wave coupling and weak turbulence of kinetic Alfven waves

摘要

The nonlinear dynamics of kinetic-Alfven-wave (KAW) turbulence is studied. Weak KAW turbulence induced by three-wave interaction among parallel-propagating KAWs has a direct energy cascade in the wavenumber domain k_(s⊥) > ρ_i~(-1) and an inverse cascade in the domain k_(s⊥) < ρ_i~(-1), resulting in Kolmogorov-type spectra. W_k ～ (k_z)~(-1/2)(k_⊥)~(-p), with exponents p = 4 and p = 3.5 respectively. The interaction including antiparallel-propagating KAWs, usually most effective, results in an inverse energy cascade over the whole k_⊥ range and p = 2 (at k_⊥ < ρ_i~(-1)) and p = 3.5 (for k_⊥ > ρ_i~(-1)) spectra. Three applications concerning KAW turbulence in flaring loops, in the Earth's magnetosphere and in tokamaks are considered. It is suggested that turbulent KAW spectra are common in space plasmas.