39 research outputs found
A kinetic model for runaway electrons in the ionosphere
Electrodynamic models and measurements with satellites and incoherent scatter radars predict large field aligned current densities on one side of the auroral arcs. Different authors and different kinds of studies (experimental or modeling) agree that the current density can reach up to hundreds of &micro;A/m<sup>2</sup>. This large current density could be the cause of many phenomena such as tall red rays or triggering of unstable ion acoustic waves. In the present paper, we consider the issue of electrons moving through an ionospheric gas of positive ions and neutrals under the influence of a static electric field. We develop a kinetic model of collisions including electrons/electrons, electrons/ions and electrons/neutrals collisions. We use a Fokker-Planck approach to describe binary collisions between charged particles with a long-range interaction. We present the essential elements of this collision operator: the Langevin equation for electrons/ions and electrons/electrons collisions and the Monte-Carlo and null collision methods for electrons/neutrals collisions. A computational example is given illustrating the approach to equilibrium and the impact of the different terms (electrons/electrons and electrons/ions collisions on the one hand and electrons/neutrals collisions on the other hand). Then, a parallel electric field is applied in a new sample run. In this run, the electrons move in the z direction parallel to the electric field. The first results show that all the electron distribution functions are non-Maxwellian. Furthermore, runaway electrons can carry a significant part of the total current density, up to 20% of the total current density
Parametric decay of beam-driven Langmuir wave and enhanced ion-acoustic fluctuations in the ionosphere: a weak turbulence approach
Cavitating Langmuir Turbulence in the Terrestrial Aurora
Langmuir cavitons have been artificially produced in the earth's ionosphere,
but evidence of naturally-occurring cavitation has been elusive. By measuring
and modeling the spectra of electrostatic plasma modes, we show that natural
cavitating, or strong, Langmuir turbulence does occur in the ionosphere, via a
process in which a beam of auroral electrons drives Langmuir waves, which in
turn produce cascading Langmuir and ion-acoustic excitations and cavitating
Langmuir turbulence. The data presented here are the first direct evidence of
cavitating Langmuir turbulence occurring naturally in any space or
astrophysical plasma.Comment: 4 pages, 4 figures, published in PRL on 9 March 2012
http://link.aps.org/doi/10.1103/PhysRevLett.108.10500
Temporal evolution of two auroral arcs as measured by the Cluster satellite and coordinated ground-based instruments
A kinetic model for runaway electrons in the ionosphere
Electrodynamic models and measurements with satellites and
incoherent scatter radars predict large field aligned current
densities on one side of the auroral arcs. Different authors and
different kinds of studies (experimental or modeling) agree that
the current density can reach up to hundreds of µA/m2.
This large current density could be the cause of many phenomena
such as tall red rays or triggering of unstable ion acoustic
waves. In the present paper, we consider the issue of electrons
moving through an ionospheric gas of positive ions and neutrals
under the influence of a static electric field. We develop a
kinetic model of collisions including electrons/electrons,
electrons/ions and electrons/neutrals collisions. We use a
Fokker-Planck approach to describe binary collisions between
charged particles with a long-range interaction. We present the
essential elements of this collision operator: the Langevin
equation for electrons/ions and electrons/electrons collisions and
the Monte-Carlo and null collision methods for electrons/neutrals
collisions. A computational example is given illustrating the
approach to equilibrium and the impact of the different terms
(electrons/electrons and electrons/ions collisions on the one hand and
electrons/neutrals collisions on the other hand). Then, a parallel
electric field is applied in a new sample run. In this run, the
electrons move in the z direction parallel to the electric field.
The first results show that all the electron distribution
functions are non-Maxwellian. Furthermore, runaway electrons can
carry a significant part of the total current density, up to 20%
of the total current density