Publication date: Nov 2013
Abstract:
The possible occurrence of equilibrium off-equatorial tori in the
gravitational and electromagnetic fields of astrophysical compact
objects has been recently proved based on non-ideal magnetohydrodynamic
theory. These stationary structures can represent plausible candidates
for the modeling of coronal plasmas expected to arise in association
with accretion disks. However, accretion disk coronae are formed by a
highly diluted environment, and so the fluid description may be
inappropriate. The question is posed of whether similar off-equatorial
solutions can also be determined in the case of collisionless plasmas
for which treatment based on kinetic theory, rather than a fluid one, is
demanded. In this paper the issue is addressed in the framework of the
Vlasov-Maxwell description for non-relativistic, multi-species
axisymmetric plasmas subject to an external dominant spherical
gravitational and dipolar magnetic field. Equilibrium configurations are
investigated and explicit solutions for the species kinetic distribution
function are constructed, which are expressed in terms of generalized
Maxwellian functions characterized by isotropic temperature and
non-uniform fluid fields. The conditions for the existence of
off-equatorial tori are investigated. It is proved that these levitating
systems are admitted under general conditions when both gravitational
and magnetic fields contribute to shaping the spatial profiles of
equilibrium plasma fluid fields. Then, specifically, kinetic effects
carried by the equilibrium solution are explicitly provided and
identified here with diamagnetic energy-correction and electrostatic
contributions. It is shown that these kinetic terms characterize the
plasma equation of state by introducing non-vanishing deviations from
the assumption of thermal pressure.
Authors:
Cremaschini, Claudio; Kovář, Jiří; Slaný, Petr; Stuchlík, Zdeněk; Karas, Vladimír;