Journal
JOURNAL OF PLASMA PHYSICS
Volume 85, Issue 1, Pages -Publisher
CAMBRIDGE UNIV PRESS
DOI: 10.1017/S0022377819000114
Keywords
astrophysical plasmas; plasma dynamics; space plasma physics
Categories
Funding
- Marsden Fund [UOO1727]
- Gordon and Betty Moore Foundation [GBMF5076]
- UK STFC [ST/N000919/1]
- EPSRC [EP/M022331/1]
- Simons Investigator awards from the Simons Foundation
- NSF [AST 13-33612, AST 17-15054]
- NASA [NNX17AK63G]
- US DOE [DE-AC02-09-CH11466]
- Alfred P. Sloan Research Fellowship
- National Science Foundation [ACI-1548562]
- EPSRC [EP/R034737/1] Funding Source: UKRI
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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-beta) 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 beta greater than or similar to 1 turbulent solar wind.
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