Enhaced electromagnetic fluctuations from high-energy Electrons : a review of kappa distributions

Abstract

In the inner heliosphere, space measurements have revealed that plasma can be described by the Kappa distributions family, which are characterized by the value of κ, indicating how far plasma is from the ideal Maxwell-Boltzmann equilibrium distribution. In magnetized plasma with enough temperature, spontaneous emissions such as magnetic fluctuations can emerge when a free source of energy is available. When supra-thermal plasma species are involved, these emissions get enhanced, and the Kappa distribution family improves the description of the related non-thermal effects. However, the lack of agreement over Kappa distribution interpretations and applications highlights the need for further exploration to gain a proper understanding of their properties and applications. In this work, we present a systematic and quantitative comparison of Kappa distributed magnetized plasma with the Original-Olbertian and Modified versions of Kappa distributions through electromagnetic fluctuations in different temperature anisotropy (A), plasma beta (β), and kappa value (κ) scenarios. Our results show that Olbertian-Kappa electron species exhibit high energy levels that scale with increasing values of β and decreasing values of κ, even when the same thermal speed is considered for all studied cases. Conversely, Modified-Kappa supra-thermal electron species exhibit less total magnetic energy results with lower kappa values, even when compared to the Maxwell distribution equilibrium results in the same macroscopic parameter configuration. This work demonstrates quantitative differences in the spectrum of magnetic fluctuations when Kappa distributions are involved. With this study, we aim to provide a powerful spectrum analysis tool to gain insights about κ-distributed plasma in space via indirect measurements of fluctuating field correlations