Modeling thin current sheets in the tail of Earth's magnetosphere and
laboratory plasmas

 Mikhail Sitnov

The thickness of the current sheets in the tail of Earth's magnetosphere
and recent reconnection experiments, such as the Magnetic Reconnection
Experiment (MRX), can be comparable to the thermal ion gyroradius in the
field outside the sheet. In such sheets the ion dynamics becomes
drastically different from the simple Larmor gyration typical for
electrons. This difference in electron and ion dynamics results in a
number of interesting new effects. In particular, the thin current sheet
(TCS) may be embedded in a thicker anisotropic plasma sheet with
counter-streaming ion flows or the TCS may have a bifurcated structure
with two current density peaks separated by a current depression region at
the sheet center. Such bifurcated sheets have been found recently in the
Earth's magnetotail due to the four-spacecraft Cluster observations, which
allowed for the first time the separation of spatial and temporal
variability.

Thus the standard Harris equilibrium model, which was used for years in
current sheet and reconnection studies, needs to be extended.  In this
talk I will discuss a new equilibrium model for TCS that generalizes the
Harris equilibrium. The stability of this new equilibrium is being
investigated by the massively parallel particle code P3D. First results
from these simulations will be presented.