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Annales Geophysicae An interactive open-access journal of the European Geosciences Union
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Volume 33, issue 3 | Copyright

Special issue: Dynamic processes in geospace

Ann. Geophys., 33, 279-293, 2015
© Author(s) 2015. This work is distributed under
the Creative Commons Attribution 3.0 License.

Regular paper 04 Mar 2015

Regular paper | 04 Mar 2015

Vlasov simulations of trapping and loss of auroral electrons

H. Gunell1, L. Andersson2, J. De Keyser1, and I. Mann3,4 H. Gunell et al.
  • 1Belgian Institute for Space Aeronomy, Avenue Circulaire 3, 1180 Brussels, Belgium
  • 2University of Colorado, Laboratory for Atmospheric and Space Physics, Boulder, CO 80309, USA
  • 3EISCAT Scientific Association, P. O. Box 812, 981 28 Kiruna, Sweden
  • 4Department of Physics, Ume\aa University, 901 87 Umeå, Sweden

Abstract. The plasma on an auroral field line is simulated using a Vlasov model. In the initial state, the acceleration region extends from one to three Earth radii in altitude with about half of the acceleration voltage concentrated in a stationary double layer at the bottom of this region. A population of electrons is trapped between the double layer and their magnetic mirror points at lower altitudes. A simulation study is carried out to examine the effects of fluctuations in the total accelerating voltage, which may be due to changes in the generator or the load of the auroral current circuit. The electron distribution function on the high potential side of the double layer changes significantly depending on whether the perturbation is toward higher or lower voltages, and therefore measurements of electron distribution functions provide information about the recent history of the voltage. Electron phase space holes are seen as a result of the induced fluctuations. Most of the voltage perturbation is assumed by the double layer. Hysteresis effects in the position of the double layer are observed when the voltage first is lowered and then brought back to its initial value.

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Short summary
In this paper, we simulate the plasma on a magnetic field line above the aurora. Initially, about half of the acceleration voltage is concentrated in a thin double layer at a few thousand km altitude. When the voltage is lowered, electrons trapped between the double layer and the magnetic mirror are released. In the process we see formation of electron beams and phase space holes. A temporary reversal of the polarity of the double layer is also seen as well as hysteresis effects in its position.
In this paper, we simulate the plasma on a magnetic field line above the aurora. Initially,...