Magnetic Spectra Comparison for Kappa-distributed Whistler Electron Fluctuations

Abstract

In the inner heliosphere, space measurements have revealed that plasma is well described by the kappa distributions, which are characterized by the value of the κ parameter. This parameter indicates how far plasma is from the ideal Maxwell–Boltzmann equilibrium distribution and gives the distribution a typical high-energy power-law tail. In these quasi-equilibrium conditions, the plasma spontaneously emits electromagnetic fluctuations. When suprathermal electrons are involved, these spontaneous emissions get enhanced, and the kappa distributions improve the description of the related nonthermal effects by taking into account the contribution of these high-energy electrons. Nevertheless, the kappa distributions describe different scenarios in which the velocity distribution may obey a power-law decay. Here, we present a systematic and quantitative comparison of kappa-distributed magnetized plasma through a comparison of magnetic spectra for electron cyclotron whistler mode fluctuations. Our results show that for a kappa distribution with a thermal speed equal to the one obtained in thermal equilibrium, the magnetic field fluctuations exhibit higher energy levels that scale with increasing values of β and decreasing values of κ , even though the same thermal speed is considered for all studied cases. Conversely, for a kappa distribution with a kappa-dependent thermal speed, the magnetic field fluctuations tend to exhibit less total energy with lower kappa values, even when compared to the Maxwellian distribution equilibrium results in the same range of parameters.

Keywords

• Plasma astrophysics
• Space plasmas
• Solar wind
• Interplanetary turbulence