Nonlinear firehose relaxation and constant-B field fluctuations

Abstract

The nonlinear evolution of Alfvénic fluctuations in the firehose unstable regime is investigated numerically and theoretically for an anisotropic plasma described by the one-fluid double adiabatic equations. We revisit the traditional theory of the instability and examine the nonlinear saturation mechanism, showing that it corresponds to evolution towards states that minimize an appropriate energy functional. We demonstrate that such states correspond to broadband magnetic and velocity field fluctuations with an overall constant magnitude of the magnetic field. These nonlinear states provide a basin of attraction for the long-term nonlinear evolution of the instability, a self-organization process that may play a role in maintaining the constant-$B$ Alfvénic states seen in the solar wind in the high-$\beta$ regime.

References in corpus (3)

• Ion kinetic energy conservation and magnetic field strength constancy in multi-fluid solar wind Alfvénic turbulence
• The parametric instability of Alfvén waves: effects of temperature anisotropy
• Subresolution Activity in Solar and Stellar Coronae from Magnetic Field Line Tangling

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• Alfvénic versus non-Alfvénic turbulence in the inner heliosphere as observed by Parker Solar Probe
• Kinetic turbulence in shining pair plasma: intermittent beaming and thermalization by radiative cooling
• Magneto-immutable turbulence in weakly collisional plasmas
• Particle-In-Cell simulations of the parallel proton firehose instability influenced by the electron temperature anisotropy in solar wind conditions
• Kinetic equilibrium of two-dimensional force-free current sheets
• Switchbacks near Boundaries of Small-scale Magnetic Flux Ropes in the Young Solar Wind from Parker Solar Probe Observations