Interplanetary and interstellar plasma turbulence
A. A. Schekochihin (Cambridge & Imperial), S. C. Cowley (UCLA &, Imperial), W. Dorland (Maryland)

TL;DR
This paper reviews theoretical models of low-frequency plasma turbulence in astrophysical environments, emphasizing kinetic theory and anisotropy, and discusses cascades from large to electron scales in solar wind and interstellar media.
Contribution
It systematically derives reduced analytical models for plasma turbulence, including hybrid fluid-kinetic descriptions and cascade processes across different scales.
Findings
Alfven waves decouple from density and magnetic fluctuations above ion gyroscale.
Hybrid fluid-kinetic model describes turbulence independently of collisionality.
Kinetic Alfven wave cascade occurs below ion gyroscale, damped at electron gyroscale.
Abstract
Theoretical approaches to low-frequency magnetized turbulence in collisionless and weakly collisional astrophysical plasmas are reviewed. The proper starting point for an analytical description of these plasmas is kinetic theory, not fluid equations. The anisotropy of the turbulence is used to systematically derive a series of reduced analytical models. Above the ion gyroscale, it is shown rigourously that the Alfven waves decouple from the electron-density and magnetic-field-strength fluctuations and satisfy the Reduced MHD equations. The density and field-strength fluctuations (slow waves and the entropy mode in the fluid limit), determined kinetically, are passively mixed by the Alfven waves. The resulting hybrid fluid-kinetic description of the low-frequency turbulence is valid independently of collisionality. Below the ion gyroscale, the turbulent cascade is partially converted…
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Taxonomy
TopicsSolar and Space Plasma Dynamics · Ionosphere and magnetosphere dynamics · Magnetic confinement fusion research
