Journal
ASTROPHYSICAL JOURNAL
Volume 847, Issue 1, Pages -Publisher
IOP Publishing Ltd
DOI: 10.3847/1538-4357/aa894d
Keywords
plasmas; solar wind; turbulence
Categories
Funding
- European Research Council under the European Union's Seventh Framework Programme (FP7)/ERC Grant [277870]
- MIT's Charles E. Reed Faculty Initiative Fund
- NSF-DOE [DE-SC0016215]
- NSF [1654168]
- Office of Science of the U.S. Department of Energy [DE-AC02-05CH11231]
- Department of Energy
- Direct For Mathematical & Physical Scien
- Division Of Physics [1654168] Funding Source: National Science Foundation
- U.S. Department of Energy (DOE) [DE-SC0016215] Funding Source: U.S. Department of Energy (DOE)
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We report the results of a direct comparison between different kinetic models of collisionless plasma turbulence in two spatial dimensions. The models considered include a first-principles fully kinetic (FK) description, two widely used reduced models (gyrokinetic (GK) and hybrid-kinetic (HK) with fluid electrons), and a novel reduced gyrokinetic approach (KREHM). Two different ion beta (bi) regimes are considered: 0.1 and 0.5. For beta i = 0.5, good agreement between the GK and FK models is found at scales ranging from the ion to the electron gyroradius, thus providing firm evidence for a kinetic Alfven cascade scenario. In the same range, the HK model produces shallower spectral slopes, presumably due to the lack of electron Landau damping. For bi = 0.1, a detailed analysis of spectral ratios reveals a slight disagreement between the GK and FK descriptions at kinetic scales, even though kinetic Alfven fluctuations likely still play a significant role. The discrepancy can be traced back to scales above the ion gyroradius, where the FK and HK results seem to suggest the presence of fast magnetosonic and ion Bernstein modes in both plasma beta regimes, but with a more notable deviation from GK in the low-beta case. The identified practical limits and strengths of reduced-kinetic approximations, compared here against the FK model on a case-by-case basis, may provide valuable insight into the main kinetic effects at play in turbulent collisionless plasmas, such as the solar wind.
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