Abstract
Using large resolution numerical simulations of gyrokinetic (GK) turbulence, spanning an interval ranging from the end of the fluid scales to the electron gyroradius, we study the energy transfers in the perpendicular direction for a proton–electron plasma in a slab equilibrium magnetic geometry. The plasma parameters employed here are relevant to kinetic Alfvén wave turbulence in solar wind conditions. In addition, we use an idealized test representation for the energy transfers between two scales, to aid our understanding of the diagnostics applicable to the nonlinear cascade in an infinite inertial range. For GK turbulence, a detailed analysis of nonlinear energy transfers that account for the separation of energy exchanging scales is performed. Starting from the study of the energy cascade and the scale locality problem, we show that the general nonlocal nature of GK turbulence, captured via locality functions, contains a subset of interactions that are deemed local, are scale invariant (i.e. a sign of asymptotic locality) and possess a locality exponent that can be recovered directly from measurements on the energy cascade. It is the first time that GK turbulence is shown to possess an asymptotic local component, even if the overall locality of interactions is nonlocal. The results presented here and their implications are discussed from the perspective of previous findings reported in the literature and the idea of universality of GK turbulence.
Highlights
Plasma turbulence is ubiquitous, being found in astrophysical [1] and laboratory [2] settings
Starting from the study of the energy redistribution and the scale locality problem, we show that the general nonlocal nature of GK turbulence, captured via locality functions, contains a subset of interactions that are deemed local, are scale invariant and possess an exponent that can be recovered directly from the interaction of solely energy exchanging scales
We first mention that in the UV limit, the locality exponents for the nonlinear interactions and the asymptotic locality exponents found for the energy cascade recover the same 5/2 value for both ions and electrons
Summary
Plasma turbulence is ubiquitous, being found in astrophysical [1] and laboratory [2] settings. Only in the early 90’s did numerical simulations allow the diagnostics that measure the transfers between two scales to be computed directly from the nonlinear terms, and the direct and local character of the cascade to be shown explicitly These diagnostics were introduced for neutral fluid turbulence [41,42,43,44], ported to drift-wave plasma turbulence [45, 46] and latter extensively used for MHD turbulence [47,48,49,50,51,52,53,54]. We try to clarify the ideas and definitions related to locality in turbulence
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