Abstract
Abstract. Wavevector anisotropy of ion-scale plasma turbulence is studied at various values of ion beta. Two complementary methods are used. One is multi-point measurements of magnetic field in the near-Earth solar wind as provided by the Cluster spacecraft mission, and the other is hybrid numerical simulation of two-dimensional plasma turbulence. Both methods demonstrate that the wavevector anisotropy is reduced with increasing values of ion beta. Furthermore, the numerical simulation study shows the existence of a scaling law between ion beta and the wavevector anisotropy of the fluctuating magnetic field that is controlled by the thermal or hybrid particle-in-cell simulation noise. Likewise, there is weak evidence that the power-law scaling can be extended to the turbulent fluctuating cascade. This fact can be used to construct a diagnostic tool to determine or to constrain ion beta using multi-point magnetic field measurements in space.
Highlights
Wavevector anisotropy appears in collisionless plasma turbulence whenever a large-scale magnetic field is present.Anisotropy is characterized by extension or elongation of the energy spectrum in the direction parallel or perpendicular to the large-scale field
The numerical simulation study shows the existence of a scaling law between ion beta and the wavevector anisotropy of the fluctuating magnetic field that is controlled by the thermal or hybrid particle-in-cell simulation noise
By extending the method and the result obtained in Narita et al (2014), we find a transition in the wavevector anisotropy as a function of ion beta
Summary
Wavevector anisotropy appears in collisionless plasma turbulence whenever a large-scale magnetic field is present.Anisotropy is characterized by extension or elongation of the energy spectrum in the direction parallel or perpendicular to the large-scale field. Examples of wavevector anisotropy can be found in near-Earth solar wind (e.g., Matthaeus et al, 1990; Chen et al, 2012), astrophysical systems such as diffusion of galactic cosmic ray (Bieber et al, 1994, 1996; Ahlers, 2014) and magnetic field decay process in the neutron star crust (Cumming et al, 2004), as well as in laboratory plasmas (Howes et al, 2012; Drake et al, 2013) All these studies conclude that plasma turbulence is primarily anisotropic such that the energy spectrum is extended preferentially in the perpendicular direction to the mean magnetic field. Most of numerical simulation studies show the perpendicular extension of the spectrum on those scales: magnetohydrodynamic turbulence (Shebalin et al, 1983; Matthaeus et al, 1996; Matthaeus and Gosh, 1999), ion-kinetic turbulence
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