2017/11/17 by Anna Tenerani, Marco Velli, Petr Hellinger · 1 citation
Physics and Astronomy · #physics.space-ph
paper · pdf · doi:10.3847/1538-4357/aa9bef
9 pages, 9 figures. Under review
arxiv created 2017/11/17 · arxiv updated 2017/12/27
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=p0\bot/p0∥ > 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.