Spectral Characteristics Of Relativistic Distributions And Induced Whistler-wave Instability In Space Plasma

There are various types of particle motions associated with the electromagnetic field in space plasma,leading to different modes of electromagnetic waves.In an ideal thermal equilibrium state,the velocity distribution of all kinds of particles follows Maxwell distributions,and all particles have the same temperature.At this time,plasma waves are in a stable status.However,some waves may increase with time when the medium is not in the ideal state.Previous works usually uses non-relativistic Kappa distribution or Bi-Maxwell distribution.Observations show that particles in the Earth's magnetosphere deviate from the Maxwell distribution.Using the recently introduced fully relativistic Kappa-type(KT)distribution and regular Kappa distribution of energetic electrons,we have obtained formula of wave growth rate,anisotropy,electron density near resonance.Using different parameter values,we have studied characteristics of the energy spectrum,wave growth rate,electron anisotropy,and the number of resonant electrons for Kappa-type and Kappa distributions.Meanwhile,we have simulated filed-aligned propagating magnetospheric chorus wave instability driven by anisotropic hot electrons in the Earth's magnetosphere,and compare results between full relativistic and non-relativistic conditions.The simulation results show that KT distribution may obey a more reasonable power-law at relativistic energies and the thermal anisotropic electron can excite whistler wave instability in the earth's magnetosphere.Compared with the typical non-relativistic Kappa distribution,relativistic Kappa-type distribution generates less growth rates of whistler wave,more consistent with the observations at high energy ~MeV.At energy of hundreds of keV,whistler wave growth rates are close and reach the peak values for both distributions.Moreover,at high energy ~1.0 MeV both growth rate and upper cutoff frequency become smaller as loss-cone parameter l increases for the relativistic KT calculation because the significant relativistic effect reduces both resonant anisotropy and number of hot electrons.This is in contrast to the nonrelativistic Kappa distribution calculations because the non-relativistic effect enhances the resonant anisotropy as l increases.