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Ann. Geophys., 23, 853-865, 2005
www.ann-geophys.net/23/853/2005/
© European Geosciences Union 2005
Phase space structures generated by absorbing obstacles in streaming plasmas
P. Guio1 and H. L. Pécseli2,3
1Parallab, Bergen Center for Computational Science, Thormøhlensgate 55, N-5008 Bergen, Norway
2University of Oslo, Physics Department, Blindern, N-0316 Oslo, Norway
3Centre for Advanced Study, Drammensveien 78, N-0271 Oslo, Norway
Abstract. The dynamic behavior of a collisionless plasma flowing around an obstacle
is investigated by numerical methods. In the present studies,
the obstacle is formed by an absorbing cylinder,
and a 2-D electrostatic particle-in-cell simulation is used
to study the flow characteristics, with extensions to a fully 3-D
generalization of the problem demonstrated as well.
The formation of irregular filamented density depletions, oblique
to the flow, is observed. The structures form behind the
obstacle, in a region with a strong
velocity shear, but also other instability mechanisms can be identified.
The dynamics of these structures is highly dependent
on the physical parameters of the plasma, and they
can either be quasi-stationary or undergo a dynamic evolution.
The structures are found to be associated
with phase-space vortices, observed especially in the phase space spanned by
the velocity
direction perpendicular to the flow and the spatial coordinate in the same
direction. The bias of the obstacle with respect to the plasma potential
is found to be an important parameter for the dynamics of the structures, but
seemingly not for their formation as such.
The results can be of interest in the interpretation of structures in
space plasmas as observed by instrumented spacecrafts.
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