C. Cremaschini, J. C. Miller, M. Tessarotto
The physical mechanism responsible for driving accretion flows in
astrophysical accretion disks is commonly thought to be related to the
development of plasma instabilities and turbulence. A key question is therefore
the determination of consistent equilibrium configurations for accretion-disk
plasmas and investigation of their stability properties. In the case of
collisionless plasmas kinetic theory provides the appropriate theoretical
framework. This paper presents a kinetic description of low-frequency and
long-wavelength axisymmetric electromagnetic perturbations in non-relativistic,
strongly-magnetized and gravitationally-bound axisymmetric accretion-disk
plasmas in the collisionless regime. The analysis, carried out within the
framework of the Vlasov-Maxwell description, relies on stationary kinetic
solutions of the Vlasov equation which allow for the simultaneous treatment of
non-uniform fluid fields, stationary accretion flows and temperature
anisotropies. It is demonstrated that, for such solutions, no axisymmetric
unstable perturbations can exist occurring on characteristic time and space
scales which are long compared with the Larmor gyration time and radius. Hence,
these stationary configurations are actually stable against axisymmetric
kinetic instabilities of this type. As a fundamental consequence, this rules
out the possibility of having the axisymmetric magneto-rotational or thermal
instabilities to arise in these systems.
View original:
http://arxiv.org/abs/1201.1839
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