Magnetic field amplification in electron phase-space holes and related effects

TL;DR

This paper investigates how electron phase-space holes generate and amplify magnetic fields through their charge and magnetic moments, leading to magnetic filamentation and potential implications for space and astrophysical plasmas.

Contribution

It provides an exact model of magnetic field amplification by electron holes, revealing their magnetic moments, interactions, and role in magnetic filamentation in plasma environments.

Findings

Electron holes carry finite magnetic moments and generate magnetic fields.

Magnetic field amplification occurs on the flux tube of the electron hole.

Holes behave as quasi-particles with dipole interactions, influencing magnetic structure formation.

Abstract

Three-dimensional electron phase space holes are shown to be positive charges on the plasma background which produce a radial electric field and force the trapped electron component into an azimuthal drift. In this way electron holes generate magnetic fields in the hole. We solve the cylindrical hole model exactly for the hole charge, electric potential and magnetic field. In electron holes, the magnetic field is amplified on the flux tube of the hole; equivalently, in ion holes the field would be decreased. The flux tube adjacent to the electron hole is magnetically depleted by the external hole dipole field. This causes magnetic filamentation. It is also shown that holes are massive objects, each carrying a finite magnetic moment. Binary magnetic dipole interaction of these moments will cause alignment of the holes into chains along the magnetic field or, in the three-dimensional case, produce a magnetic fabric in the volume of hole formation. Since holes, in addition to being carriers of charges and magnetic moments, also have finite masses, they behave like quasi-particles, performing ExB, magnetic field, and diamagnetic drifts. In an inhomogeneous magnetic field, their magnetic moments experience torque which causes nutation of the hole around the direction of the magnetic field presumably giving rise to low frequency magnetic modulations like pulsations. A gas of many such holes may allow for a kinetic description in which holes undergo binary dipole interactions. This resembles the polymeric behaviour. Both magnetic field generation and magnetic structure formation is of interest in auroral, solar coronal and shock physics, in particular in the problem of magnetic field filamentation in relativistic foreshocks and cosmic ray acceleration.