Asymmetric configurations of a thin current sheet with a constant normal magnetic field component
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OSPHERIC PLASMA
Asymmetric Configurations of a Thin Current Sheet with a Constant Normal Magnetic Field Component O. V. Mingaleva, I. V. Mingaleva, Kh. V. Malovab, c, L. M. Zelenyic, and A. V. Artem’evc a Polar
Geophysics Institute, Kola Scientific Center, Russian Academy of Sciences, ul. Fersmana 14, Apatity, Murmansk oblast, 184209 Russia b Skobeltsyn Institute of Nuclear Physics, Moscow State University, Moscow, 119992 Russia c Space Research Institute, Russian Academy of Sciences, Profsoyuznaya ul. 84/32, Moscow, 117810 Russia Received May 5, 2008
Abstract—A possible mechanism for the formation of a quasi-equilibrium asymmetric current sheet in the magnetospheric tail due to the asymmetry of peripheral plasma sources is analyzed using a self-consistent particle-in-cell model of a thin collisionless current sheet with a constant normal magnetic field component. For the case in which the current sheet is produced by only one source, quasi-equilibrium sheet configurations with maximum possible asymmetry are obtained for different input parameters of the model. In such configurations, the equilibrium force balance is satisfied with high accuracy and the shape of the current density profile remains nearly symmetric, but the current sheet itself is slightly shifted from the source as compared to the symmetric case. The configurations obtained using numerical simulations are compared with those calculated using the previous analytical model of a thin current sheet. It is found that the results provided by these models agree well both qualitatively and quantitatively. PACS numbers: 94.30.cl, 94.30.ct, 94.05.-a DOI: 10.1134/S1063780X09010097
1. INTRODUCTION
ture and dynamics are of great importance. Experiments have shown that the thickness of TCSs in the Earth’s magnetotail filled with a hot collisionless plasma is a few plasma ion gyroradii (from 250 to 1500–2000 km) [4–7]. Figure 1 schematically shows a possible configuration of magnetic field lines that is observed during a substorm in the magnetospheric tail under the conditions in which there is a neutral line at the current sheet edge nearest to the Earth (15–20RE). Hereinafter, we use the GSM coordinate system, in which the X axis is directed from the Earth to the Sun; the Y axis, from East to West; and the Z axis, from South to North. The light-grey square denotes a plasma sheet between the neutral lines. The regions of the max-
An important problem of space physics that has not yet been solved completely is the initiation and nonlinear bursty dynamics of plasma perturbations (magnetic substorms) in the Earth’s magnetosphere. Such perturbations take place at different time and spatial scales, from global perturbations involving the entire magnetosphere to small-scale perturbations with dimensions on the order of the electron inertial length. It is assumed that a key role in the development of substorms is played by thin current sheets (TCSs) in the Earth’s magnetotail, which have been actively studied during the past decade [1–4]. It was found that TCSs can
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