Fully Kinetic versus Reduced-kinetic Modeling of Collisionless Plasma Turbulence

Journal Article · Wed Sep 20 00:00:00 EDT 2017 · The Astrophysical Journal (Online)

DOI:https://doi.org/10.3847/1538-4357/aa894d· OSTI ID:1524231

Grošelj, Daniel  ^[1]; Cerri, Silvio S.  ^[2]; Navarro, Alejandro Bañón ^[1]; Willmott, Christopher ^[3]; Told, Daniel  ^[4]; Loureiro, Nuno F.  ^[3]; Califano, Francesco  ^[2]; Jenko, Frank ^[1]

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1. Max-Planck-Inst. fur Plasmaphysik, Garching (Germany); Univ. of California, Los Angeles, CA (United States). Dept. of Physics and Astronomy
2. Univ. of Pisa, Pisa (Italy). Physics Dept. "E. Fermi"
3. Massachusetts Inst. of Technology (MIT), Cambridge, MA (United States). Plasma Science and Fusion Center
4. Max-Planck-Inst. fur Plasmaphysik, Garching (Germany)

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 ($${\beta }_{i}$$) 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 Alfvén cascade scenario. In the same range, the HK model produces shallower spectral slopes, presumably due to the lack of electron Landau damping. For $${\beta }_{i}=0.1$$, a detailed analysis of spectral ratios reveals a slight disagreement between the GK and FK descriptions at kinetic scales, even though kinetic Alfvén 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. As a result, 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.

• Research Organization: Lawrence Berkeley National Laboratory (LBNL), Berkeley, CA (United States). National Energy Research Scientific Computing Center (NERSC)
• Sponsoring Organization: USDOE
• OSTI ID: 1524231
• Journal Information: The Astrophysical Journal (Online), Vol. 847, Issue 1; ISSN 1538-4357
• Publisher: Institute of Physics (IOP)
• Country of Publication: United States
• Language: English

Related Subjects

79 ASTRONOMY AND ASTROPHYSICS
plasmas
solar wind
turbulence