Self-organization in collisionless, high-β turbulence

Journal Article · 11 November 2024 · Journal of Plasma Physics

DOI: https://doi.org/10.1017/s0022377824001296 · OSTI ID:2479850

Majeski, S.  ^[1]; Kunz, M. W.  ^[1]; Squire, J.  ^[2]

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1. Princeton Univ., NJ (United States); Princeton Plasma Physics Laboratory (PPPL), Princeton, NJ (United States)
2. University of Otago (New Zealand)

The magnetohydrodynamic (MHD) equations, as a collisional fluid model that remains in local thermodynamic equilibrium (LTE), have long been used to describe turbulence in myriad space and astrophysical plasmas. Yet, the vast majority of these plasmas, from the solar wind to the intracluster medium (ICM) of galaxy clusters, are only weakly collisional at best, meaning that significant deviations from LTE are not only possible but common. Recent studies have demonstrated that the kinetic physics inherent to this weakly collisional regime can fundamentally transform the evolution of such plasmas across a wide range of scales. Here, we explore the consequences of pressure anisotropy and Larmor-scale instabilities for collisionless, β $$\gg$$ 1, turbulence, focusing on the role of a self-organizational effect known as ‘magneto-immutability’. We describe this self-organization analytically through a high-β, reduced ordering of the Chew–Goldberger–Low-MHD (CGL-MHD) equations, finding that it is a robust inertial-range effect that dynamically suppresses magnetic-field-strength fluctuations, anisotropic-pressure stresses and dissipation due to heat fluxes. As a result, the turbulent cascade of Alfvénic fluctuations continues below the putative viscous scale to form a robust, nearly conservative, MHD-like inertial range. These findings are confirmed numerically via Landau-fluid CGL-MHD turbulence simulations that employ a collisional closure to mimic the effects of microinstabilities. We find that microinstabilities occupy a small (~5%) volume-filling fraction of the plasma, even when the pressure anisotropy is driven strongly towards its instability thresholds. We discuss these results in the context of recent predictions for ion-vs-electron heating in low-luminosity accretion flows and observations implying suppressed viscosity in ICM turbulence.

• Research Organization: Princeton Plasma Physics Laboratory (PPPL), Princeton, NJ (United States)
• Sponsoring Organization: USDOE
• OSTI ID: 2479850
• Journal Information: Journal of Plasma Physics, Journal Name: Journal of Plasma Physics Journal Issue: 6 Vol. 90; ISSN 0022-3778
• Publisher: Cambridge University PressCopyright Statement
• Country of Publication: United States
• Language: English