The evolution of the magnetic structures in electron phase-space holes: Two-dimensional particle-in-cell simulations

Abstract

Observations have shown that electron phase-space holes (electron holes) possess regular magnetic structures. In this paper, two-dimensional (2D) electromagnetic particle-in-cell (PIC) simulations are performed in the (x, y) plane to study magnetic structures associated with electron holes under different plasma conditions. In the simulations, the background magnetic field (B0 = B0ex) is along the x direction. The combined actions between the transverse instability and stabilization by the background magnetic field lead to the generation of the electric field E y. Then electrons suffer the electric field drift and produce the current in the z direction, which leads to the fluctuating magnetic field along the x and y directions. Meanwhile, the motion of the electron holes along the x direction and the existence of the electric field Ey generate the fluctuating magnetic field along the z direction. In very weakly magnetized plasma (Ωe < ωpe, where Ωe and ωpe are the electron gyrofrequency and electron plasma frequency, respectively.), the transverse instability is very strong and the magnetic structures associated with electron holes disappear quickly. When Ωe is comparable to ωpe, the parallel cut of the fluctuating magnetic field δBx and δBz has unipolar structures in the electron holes, while the parallel cut of fluctuating magnetic field δBy has bipolar structures. In strongly magnetized plasma (ωe > pe), electrostatic whistler waves with streaked structures of Ey are excited. The fluctuating magnetic field δBx and δB z also have streaked structures. The relevance between our simulation results and the magnetic structures associated with electron holes observed in the plasma sheet is also discussed. Copyright 2011 by the American Geophysical Union.