Nonquasineutral electron vortices in nonuniform plasmas

Electron vortices are observed in the numerical simulation of current carrying plasmas on fast time scales where the ion motion can be ignored. In plasmas with nonuniform density n, vortices drift in the B × ∇n direction with a speed that is on the order of the Hall speed. This provides a mechanism...

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Bibliographic Details
Published in:Physics of plasmas 2014-11, Vol.21 (11)
Main Authors: Angus, J. R., Richardson, A. S., Ottinger, P. F., Swanekamp, S. B., Schumer, J. W.
Format: Article
Language:English
Subjects:
70 PLASMA PHYSICS AND FUSION TECHNOLOGY
Charge density
Computational fluid dynamics
Computer simulation
COMPUTERIZED SIMULATION
Current carrying plasmas
DEBYE LENGTH
Drift
ELECTRONS
Fluid flow
Ion motion
Magnetohydrodynamics
Mathematical models
Nonuniform plasmas
PLASMA
Plasma physics
Rotating plasmas
VELOCITY
Velocity distribution
VORTICES
Vorticity
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Summary:Electron vortices are observed in the numerical simulation of current carrying plasmas on fast time scales where the ion motion can be ignored. In plasmas with nonuniform density n, vortices drift in the B × ∇n direction with a speed that is on the order of the Hall speed. This provides a mechanism for magnetic field penetration into a plasma. Here, we consider strong vortices with rotation speeds Vϕ close to the speed of light c where the vortex size δ is on the order of the magnetic Debye length λB=|B|/4πen and the vortex is thus nonquasineutral. Drifting vortices are typically studied using the electron magnetohydrodynamic model (EMHD), which ignores the displacement current and assumes quasineutrality. However, these assumptions are not strictly valid for drifting vortices when δ ≈ λB. In this paper, 2D electron vortices in nonuniform plasmas are studied for the first time using a fully electromagnetic, collisionless fluid code. Relatively large amplitude oscillations with periods that correspond to high frequency extraordinary modes are observed in the average drift speed. The drift speed W is calculated by averaging the electron velocity field over the vorticity. Interestingly, the time-averaged W from these simulations matches very well with W from the much simpler EMHD simulations even for strong vortices with order unity charge density separation.
ISSN:1070-664X
1089-7674
DOI:10.1063/1.4902101