Parametric instability of nonlinear Alfvén waves in anisotropic plasmas
Abstract
We study the stability of large amplitude, circularly polarized Alfvén waves in an anisotropic plasma described by the double adiabatic two-temperature CGL equations, and in particular the effect of a background pressure anisotropy on the well-known properties of Alfvén wave parametric decay in Magnetohydrodynamics (MHD). A temperature anisotropy allows instability over a much wider range of values of parallel plasma beta (β||) when the pressure anisotropy p0perp/p0|| > 1. For p0perp/p0|| > 2.7 there is a new regime in which the growth rates of the parametric instability become finite and independent of β|| in the limit β||>>1. In the opposite case of p0perp/p0|| < 2.7, the instability is strongly suppressed for increasing plasma beta, similar to the MHD case. We analyze marginal stability conditions for parametric and firehose instabilities in parameter space defined by p0perp/p0|| vs. β|| and the wave amplitude B vs. β||, and discuss possible implications for Alfvén waves in the solar wind. We validate our results by means of hybrid simulations and we show under which conditions the parametric decay is unaffected by the onset of kinetic instabilities at smaller scales.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2017
- Bibcode:
- 2017AGUFMSH14B..05T
- Keywords:
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- 2164 Solar wind plasma;
- INTERPLANETARY PHYSICS;
- 2169 Solar wind sources;
- INTERPLANETARY PHYSICS;
- 7509 Corona;
- SOLAR PHYSICS;
- ASTROPHYSICS;
- AND ASTRONOMY;
- 7524 Magnetic fields;
- SOLAR PHYSICS;
- ASTROPHYSICS;
- AND ASTRONOMY