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Title: Conditions for establishing quasistable double layers in the Earth's auroral upward current region

Abstract

The strength and stability of simulated double layers at the ionosphere-auroral cavity boundary have been studied as a function of cold ionospheric electron temperature and density. The simulations are performed with an open boundary one-dimensional particle-in- cell (PIC) simulation and are initialized by imposing a density cavity within the simulation domain. The PIC simulation includes H{sup +} and O{sup +} ion beams, a hot H{sup +} background population, cold ionospheric electrons, and a hot electron population. It is shown that a double layer remains quasistable for a variety of initial conditions and plasma parameters. The average potential drop of the double layer is found to increase as the cold electron temperature decreases. However, in terms of cold electron density, the average potential drop of the double layer is found to increase up to some critical cold electron density and decreases above this value. Comparisons with FAST observations are made and agreement is found between simulation results and observations in the shape and width of the double layer. This study helps put a constraint on the plasma conditions in which a DL can be expected to form and remain quasistable.

Authors:
 [1];  [2];  [3]
  1. Department of Physics, John Brown University, Siloam Springs, Arkansas 72761 (United States)
  2. Center for Integrated Plasma Studies, University of Colorado, Boulder, Colorado 80309 (United States)
  3. Laboratory for Atmospheric and Space Physics, University of Colorado, Boulder, Colorado 80303 (United States)
Publication Date:
OSTI Identifier:
21532102
Resource Type:
Journal Article
Resource Relation:
Journal Name: Physics of Plasmas; Journal Volume: 17; Journal Issue: 12; Other Information: DOI: 10.1063/1.3520058; (c) 2010 American Institute of Physics
Country of Publication:
United States
Language:
English
Subject:
70 PLASMA PHYSICS AND FUSION TECHNOLOGY; ELECTRON DENSITY; ELECTRON TEMPERATURE; ELECTRONS; HYDROGEN IONS 1 PLUS; ION BEAMS; IONOSPHERE; LAYERS; OXYGEN IONS; PLASMA SHEATH; PLASMA SIMULATION; BEAMS; CATIONS; CHARGED PARTICLES; EARTH ATMOSPHERE; ELEMENTARY PARTICLES; FERMIONS; HYDROGEN IONS; IONS; LEPTONS; SIMULATION

Citation Formats

Main, D. S., Newman, D. L., and Ergun, R. E. Conditions for establishing quasistable double layers in the Earth's auroral upward current region. United States: N. p., 2010. Web. doi:10.1063/1.3520058.
Main, D. S., Newman, D. L., & Ergun, R. E. Conditions for establishing quasistable double layers in the Earth's auroral upward current region. United States. doi:10.1063/1.3520058.
Main, D. S., Newman, D. L., and Ergun, R. E. 2010. "Conditions for establishing quasistable double layers in the Earth's auroral upward current region". United States. doi:10.1063/1.3520058.
@article{osti_21532102,
title = {Conditions for establishing quasistable double layers in the Earth's auroral upward current region},
author = {Main, D. S. and Newman, D. L. and Ergun, R. E.},
abstractNote = {The strength and stability of simulated double layers at the ionosphere-auroral cavity boundary have been studied as a function of cold ionospheric electron temperature and density. The simulations are performed with an open boundary one-dimensional particle-in- cell (PIC) simulation and are initialized by imposing a density cavity within the simulation domain. The PIC simulation includes H{sup +} and O{sup +} ion beams, a hot H{sup +} background population, cold ionospheric electrons, and a hot electron population. It is shown that a double layer remains quasistable for a variety of initial conditions and plasma parameters. The average potential drop of the double layer is found to increase as the cold electron temperature decreases. However, in terms of cold electron density, the average potential drop of the double layer is found to increase up to some critical cold electron density and decreases above this value. Comparisons with FAST observations are made and agreement is found between simulation results and observations in the shape and width of the double layer. This study helps put a constraint on the plasma conditions in which a DL can be expected to form and remain quasistable.},
doi = {10.1063/1.3520058},
journal = {Physics of Plasmas},
number = 12,
volume = 17,
place = {United States},
year = 2010,
month =
}
  • The dynamic evolution of the boundary between the ionosphere and auroral cavity is studied using 1D and 2D kinetic Vlasov simulations. The initial distributions of three singly ionized species (H{sup +}, O{sup +}, e{sup -}) are determined from space-based observations on both sides of an inferred strong double layer. The kinetic simulations reproduce features of parallel electric fields, electron distributions, ion distributions, and wave turbulence seen in satellite observations in the auroral upward-current region and, for the first time, demonstrate that auroral acceleration can be driven by a parallel electric field supported, in part, by a quasistable, strong double layer.more » In addition, the simulations verify that the streaming interaction between accelerated O{sup +} and H{sup +} populations continuously replenished by the double layer provides the free energy for the persistent formation of ion phase-space holes.« less
  • The formation and evolution of ion acoustic solitons in Earth's auroral upward current region are studied using one- and two-dimensional (2D) electrostatic particle-in-cell simulations. The one-dimensional simulations are confined to processes that occur in the auroral cavity and include four plasma populations: hot electrons, H{sup +} and O{sup +} anti-earthward ion beams, and a hot H{sup +} background population. Ion acoustic solitons are found to form for auroral-cavity ion beams consistent with acceleration through double-layer (DL) potentials measured by FAST. A simplified one-dimensional model simulation is then presented in order to isolate the mechanisms that lead to the formation ofmore » the ion acoustic soliton. Results of a two-dimensional simulation, which include both the ionosphere and the auroral cavity, separated by a low-altitude DL, are then presented in order to confirm that the soliton forms in a more realistic 2D geometry. The 2D simulation is initialized with a U-shaped potential structure that mimics the inferred shape of the low altitude transition region based on observations. In this simulation, a soliton localized perpendicular to the geomagnetic field is observed to form and reside next to the DL. Finally, the 2D simulation results are compared with FAST data and it is found that certain aspects of the data can be explained by assuming the presence of an ion acoustic soliton.« less
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  • Numerical simulations showed recurring interruption and recovery of electron and ion currents through double layers. The time period tau of the recurring phenomena is governed by the ion dynamics; for ions with a drift V/sub i/ entering the simulation plasma such that V/sub i/< or approx. =V/sub ti/, the ion thermal speed, tau is governed by the ion transit time from the location of ion injection to the location of the double layer. On the other hand, when V/sub i/>V/sub ti/ ion-acoustic modes also appear in the electron- and ion-current fluctuations. The electron current fluctuations are governed by the ionmore » current through the Langmuir criterion. It is suggested that some low frequency auroral fluctuations could possibly be explained by current fluctuations through double layers.« less
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