Oblate Electron Holes are not attributable to Anisotropic Shielding

TL;DR

This paper demonstrates that oblate electron holes are not caused by anisotropic shielding but rather by isotropic shielding, challenging previous models and supported by theoretical analysis and particle-in-cell simulations.

Contribution

It clarifies the shielding mechanism behind electron hole shapes, showing isotropic shielding explains their properties better than anisotropic models.

Findings

Gyrokinetic model based on perpendicular polarization is incorrect.

Isotropic shielding with Debye length explains electron hole potential.

Simulations confirm theoretical analysis.

Abstract

Shielding mechanisms' influence on the ratio of perpendicular to parallel scale lengths of multidimensional plasma electron hole equilibria are analyzed theoretically and computationally. It is shown that the ``gyrokinetic'' model, invoking perpendicular polarization, is based on a misunderstanding and cannot explain the observational trend that greater transverse extent accompanies lower magnetic field. Instead, the potential in the wings of the hole, outside the region of trapped-electron depletion, has isotropic shielding giving $\phi\propto {\rm e}^{-r/L}/r$, with the shielding length $L$ equal to the Debye length for holes much slower than the electron thermal speed. Particle in cell simulations confirm the analysis.