Dynamic Phase Alignment in Inertial Alfven Turbulence

Abstract

In weakly-collisional plasma environments with sufficiently low electron beta, Alfvénic turbulence transforms into inertial Alfvénic turbulence at scales below the electron skin-depth, $k_{\perp }{d}_e\gtrsim 1$. We argue that, in inertial Alfvénic turbulence, both energy and generalized kinetic helicity exhibit direct cascades. We demonstrate that the two cascades are compatible due to the existence of a strong scale-dependence of the phase alignment angle between velocity and magnetic field fluctuations, with the phase alignment angle scaling as $\cos {\alpha }_k\propto k_{\perp }^{-1}$. The kinetic and magnetic energy spectra scale as $\propto k_{\perp }^{-5/3}$ and $\propto k_{\perp }^{-11/3}$, respectively. As a result of the dual direct cascade, the generalized-helicity spectrum scales as $\propto k_{\perp }^{-5/3}$, implying progressive balancing of the turbulence as the cascade proceeds to smaller scales in the $k_{\perp }{d}_e\gg 1$ range. Turbulent eddies exhibit a phase-space anisotropy $k_{\parallel }\propto k_{\perp }^{5/3}$, consistent with critically-balanced inertial Alfvén fluctuations. Our results may be applicable to a variety of geophysical, space, and astrophysical environments, including the Earth's magnetosheath and ionosphere, solar corona, non-relativistic pair plasmas, as well as to strongly rotating non-ionized fluids.

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• Spectra of magnetic turbulence in a relativistic plasma
• Wave Turbulence in Inertial Electron Magnetohydrodynamics
• Dynamic Phase Alignment in Navier-Stokes Turbulence
• The effects of finite electron inertia on helicity-barrier-mediated turbulence
• Gyrofluid simulations of turbulence and reconnection in space plasmas
• Turbulent heating in collisionless low-beta plasmas: imbalance, Landau damping, and electron-ion energy partition
• Anisotropic electron heating in turbulence-driven magnetic reconnection in the near-Sun solar wind
• Whistler-Alfvén turbulence in a non-neutral ultrarelativistic pair plasma