Kinetic models of sub-ion cylindrical magnetic hole

Abstract

Magnetic holes are magnetoplasma structures very similar to the classical θ–pinch. They are widely observed in the space plasma and identified by the substantial magnetic field depressions on scales from magnetohydrodynamic range to electron scales. In this paper, we develop the kinetic models of cylindrically symmetric magnetic holes with sub-ion scales using two types of charged particle distribution functions (both current-carrying and background plasma populations are included). We demonstrate that developed magnetic holes have configurations very similar to those revealed in the recent spacecraft observations in the Earth magnetosphere: both localized electron currents and strong radial electric fields are found at the magnetic hole boundary. We demonstrate that for realistic plasma parameters, the inclusion of ion currents into the model produces magnetic holes with double-scale magnetic field profile. We find that the magnetic hole depth (amplitude of the magnetic field depression) depends on the magnetic hole typical radius. Possible applications of developed models are discussed.

Self-consistent kinetic model of nested electron- and ion-scale magnetic cavities in space plasmas

“…The invariants of motion used in ref. 46 are the particle energy and the canonical angular momentum in the azimuthal direction. To account for the electron perpendicular anisotropy, we adopt another invariant of electron motion, the magnetic moment μ (which depends on perpendicular but not parallel velocity).…”

“…Our model is developed in cylindrical coordinates ( ρ , φ , z ), which is adapted to conform to the circular cross-sections of magnetic cavities in both simulations 43 and observations 16 , 20 . In deriving a kinetic equilibrium state consistent with observations, proton and electron distributions must be taken as functions of the invariants of particle motion 46 , 48 , 49 so as to satisfy the Vlasov equation. The invariants of motion used in ref.…”

“…We next follow ref. 46 to assume that each species have two distinct components, a background population and a current-carrying population (represented by subscripts 0 and 1, respectively), so the particle distribution functions can be given by…”

“…The deadlock to resolve the two-or three-dimensional configurations can only be solved by comprehensive models of magnetic cavities. According to a recently proposed kinetic model 46 , magnetic cavities are analogous to classical theta-pinches 47 in laboratory plasmas, with their electromagnetic and particle profiles determined by Vlasov-Maxwell equations in cylindrical coordinates. Many model features, such as the nested structures, ring-shaped current, and enhanced plasma pressure, are all present in spacecraft observations.…”

Study of the Electron Velocity Inside Sub‐Ion‐Scale Magnetic Holes in the Solar Wind by MMS Observations

“…Magnetic holes in the solar wind at 1 AU are believed to originate from corona (Russell et al, 2008), suggesting that there is a stabilizing mechanism to keep them survive for a long life time. The azimuthal current density contributed by electrons is a potential candidate to maintain the stability of their structure (Haynes et al, 2015;Shustov et al, 2016Shustov et al, , 2019. Therefore, a detailed study of the electron velocity inside the magnetic hole is of great significance to reveal its stability.…”