The Parametric Instability of Alfvén Waves: Effects of Temperature Anisotropy
Abstract
We study the stability of large-amplitude, circularly polarized Alfvén waves in an anisotropic plasma described by the double-adiabatic/CGL closure, and in particular the effect of a background thermal pressure anisotropy on the well-known properties of Alfvén wave parametric decay in magnetohydrodynamics (MHD). Anisotropy allows instability over a much wider range of values of parallel plasma beta (β ∥) when ξ = p 0⊥/p 0∥ > 1. When the pressure anisotropy exceeds a critical value, ξ ≥ ξ* with ξ* ≃ 2.7, there is a new regime in which the parametric instability is no longer quenched at high β ∥, and in the limit β ∥ ≫ 1, the growth rate becomes independent of β ∥. In the opposite case of ξ < ξ*, the instability is strongly suppressed with increasing parallel plasma beta, similarly to the MHD case. We analyze marginal stability conditions for parametric decay in the (ξ, β ∥) parameter space and discuss possible implications for Alfvénic turbulence in the solar wind.
- Publication:
-
The Astrophysical Journal
- Pub Date:
- December 2017
- DOI:
- 10.3847/1538-4357/aa9bef
- arXiv:
- arXiv:1711.06371
- Bibcode:
- 2017ApJ...851...99T
- Keywords:
-
- instabilities;
- plasmas;
- Sun: heliosphere;
- waves;
- Physics - Space Physics
- E-Print:
- 9 pages, 9 figures. Under review