Wave induced suprathermal tail generation of electron velocity space distributions

Observed velocity space distributions of magnetospheric and coronal electron and proton spectra are well represented by a power law in particle speed and are commonly modeled by a κ-distribution. The non-Maxwellian, superthermal tails of such distributions may result from an acceleration mechanism by wave–particle interaction due to the presence of broadband lower hybrid or Alfvén wave turbulence. In the latter context, the problem of charged particle dragging by plasma waves is modeled within the Fokker–Planck formalism, where the velocity space diffusion is induced by the Cherenkov interaction. The numerical simulation of the temporal evolution of the distribution function is discussed on the basis of a wave driven acceleration process, possibly saturated by collisional drag. From the time evolution of the electron distribution function it is demonstrated that in particular Alfvén wave interaction generates a superthermal particle population exhibiting high energy tails, consistent with the family of κ-distributions.