Magneto-immutable turbulence in weakly collisional plasmas. (February 2019)

• Record Type: Journal Article
• Authors: Squire, J.; Schekochihin, A. A.; Quataert, E.; Kunz, M. W.
• Is Part Of: Journal of plasma physics. Volume 85:Number 1(2019)
• Publication Date: 2019-02
• Subjects: astrophysical plasmas, -- plasma dynamics, -- space plasma physics; Plasma (Ionized gases) -- Periodicals; 530.4405
• DOI: 10.1017/S0022377819000114
• Languages: English
• ISSNs: 0022-3778

Abstract

Abstract : We propose that pressure anisotropy causes weakly collisional turbulent plasmas to self-organize so as to resist changes in magnetic-field strength. We term this effect 'magneto-immutability' by analogy with incompressibility (resistance to changes in pressure). The effect is important when the pressure anisotropy becomes comparable to the magnetic pressure, suggesting that in collisionless, weakly magnetized (high- $\unicode[STIX]{x1D6FD}$ ) plasmas its dynamical relevance is similar to that of incompressibility. Simulations of magnetized turbulence using the weakly collisional Braginskii model show that magneto-immutable turbulence is surprisingly similar, in most statistical measures, to critically balanced magnetohydrodynamic turbulence. However, in order to minimize magnetic-field variation, the flow direction becomes more constrained than in magnetohydrodynamics, and the turbulence is more strongly dominated by magnetic energy (a non-zero 'residual energy'). These effects represent key differences between pressure-anisotropic and fluid turbulence, and should be observable in the $\unicode[STIX]{x1D6FD}\gtrsim 1$ turbulent solar wind.