Dynamic Phase Alignment in Inertial Alfvén Turbulence

Journal Article · Mon Dec 21 00:00:00 EST 2020 · Physical Review Letters

DOI:https://doi.org/10.1103/physrevlett.125.265101· OSTI ID:1850023

Milanese, Lucio M.  ^[1]; Loureiro, Nuno F.  ^[1]; Daschner, Maximilian  ^[2]; Boldyrev, Stanislav  ^[3]

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1. Massachusetts Inst. of Technology (MIT), Cambridge, MA (United States)
2. Massachusetts Inst. of Technology (MIT), Cambridge, MA (United States); ETH Zurich (Switzerland)
3. Univ. of Wisconsin, Madison, WI (United States); Space Science Institute, Boulder, CO (United States)

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_⊥d_e ≳ 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 α_k ∝ $$k$$$^{–1}_{⊥}$$. The kinetic and magnetic energy spectra scale as ∝ $$k$$$^{–5/3}_{⊥}$$ and ∝ $$k$$$^{–11/3}_{⊥}$$, respectively. As a result of the dual direct cascade, the generalized helicity spectrum scales as ∝ $$k$$$^{–5/3}_{⊥}$$, implying progressive balancing of the turbulence as the cascade proceeds to smaller scales in the k_⊥d_e >> 1 range. Turbulent eddies exhibit a phase-space anisotropy k_∥ ∝ $$k$$$^{5/3}_{⊥}$$, consistent with critically balanced inertial Alfvén fluctuations. Furthermore, our results may be applicable to a variety of geophysical, space, and astrophysical environments, including the Earth’s magnetosheath and ionosphere, solar corona, and nonrelativistic pair plasmas, as well as to strongly rotating nonionized fluids.

• Research Organization: Massachusetts Inst. of Technology (MIT), Cambridge, MA (United States); Univ. of Wisconsin, Madison, WI (United States); Univ. of California, Oakland, CA (United States)
• Sponsoring Organization: USDOE Office of Science (SC)
• Grant/Contract Number: FG02-91ER54109; SC0018266; AC02-05CH11231
• OSTI ID: 1850023
• Journal Information: Physical Review Letters, Vol. 125, Issue 26; ISSN 0031-9007
• Publisher: American Physical Society (APS)
• Country of Publication: United States
• Language: English

Related Subjects

70 PLASMA PHYSICS AND FUSION TECHNOLOGY
Physics
Alfvén waves
Nonlinear phenomena in plasmas
Plasma turbulence
Turbulence
Earth's magnetosphere
Magnetized plasma
Solar plasma