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⊥de ≳ 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 αk ∝ $$k$$$^{–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⊥de >> 1 range. Turbulent eddies exhibit a phase-space anisotropy k∥ ∝ $$k$$$^{5/3}_{⊥}$$, consistent with critically balanced inertial Alfvén fluctuations. Furthermore, our results may be applicable to a variety of geophysical, space, and astrophysical environments, including the Earth’s magnetosheath and ionosphere, solar corona, and nonrelativistic pair plasmas, as well as to strongly rotating nonionized fluids.
@article{osti_1850023,
author = {Milanese, Lucio M. and Loureiro, Nuno F. and Daschner, Maximilian and Boldyrev, Stanislav},
title = {Dynamic Phase Alignment in Inertial Alfvén Turbulence},
annote = {In weakly collisional plasma environments with sufficiently low electron beta, Alfvénic turbulence transforms into inertial Alfvénic turbulence at scales below the electron skin depth, k⊥de ≳ 1. We argue that, in inertial Alfvénic turbulence, both energy and generalized kinetic helicity exhibit direct cascades. We demonstrate that the two cascades are compatible due to the existence of a strong scale dependence of the phase alignment angle between velocity and magnetic field fluctuations, with the phase alignment angle scaling as cos αk ∝ $k$$^{–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$$^{–5/3}_{⊥}$, implying progressive balancing of the turbulence as the cascade proceeds to smaller scales in the k⊥de >> 1 range. Turbulent eddies exhibit a phase-space anisotropy k∥ ∝ $k$$^{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.},
doi = {10.1103/physrevlett.125.265101},
url = {https://www.osti.gov/biblio/1850023},
journal = {Physical Review Letters},
issn = {ISSN 0031-9007},
number = {26},
volume = {125},
place = {United States},
publisher = {American Physical Society (APS)},
year = {2020},
month = {12}}
Massachusetts Inst. of Technology (MIT), Cambridge, MA (United States); Univ. of Wisconsin, Madison, WI (United States); Univ. of California, Oakland, CA (United States)
Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences, Vol. 373, Issue 2041https://doi.org/10.1098/rsta.2014.0154