Overstability of acoustic waves in strongly magnetized anisotropic MHD shear flows
arXiv:1407.6943 · doi:10.1063/1.4892402
Abstract
We present a linear stability analysis of the perturbation modes in anisotropic MHD flows with velocity shear and strong magnetic field. Collisionless or weakly collisional plasma is described within the 16-momentum MHD fluid closure model, that takes into account not only the effect of pressure anisotropy, but also the effect of anisotropic heat fluxes. In this model the low frequency acoustic wave is revealed into a standard acoustic mode and higher frequency fast thermo-acoustic and lower frequency slow thermo-acoustic waves. It is shown that thermo-acoustic waves become unstable and grow exponentially when the heat flux parameter exceeds some critical value. It seems that velocity shear makes thermo-acoustic waves overstable even at subcritical heat flux parameters. Thus, when the effect of heat fluxes is not profound acoustic waves will grow due to the velocity shear, while at supercritical heat fluxes the flow reveals compressible thermal instability. Anisotropic thermal instability should be also important in astrophysical environments, where it will limit the maximal value of magnetic field that a low density ionized anisotropic flow can sustain.
arXiv commentPhys. Plasmas 21, 082902 (2014)
References in corpus (10)
- Electron Heating in Hot Accretion Flows
- The Magnetorotational Instability in a Collisionless Plasma
- Kinetic Signatures and Intermittent Turbulence in the Solar Wind Plasma
- Magnetic field amplification and evolution in turbulent collisionless MHD: an application to the ICM
- Transition from collisionless to collisional MRI
- Models of magnetic-field evolution and effective viscosity in weakly collisional extragalactic plasmas
- Wave instabilities in an anisotropic magnetized space plasma
- Wave instabilities of a collisionless plasma in fluid approximation
- On the low-frequency boundary of Sun-generated MHD turbulence in the slow solar wind
- The role of pressure anisotropy in the turbulent intracluster medium