The Alfvenic nature of energy transfer mediation in localized, strongly nonlinear Alfven wavepacket collisions

Abstract

In space and astrophysical plasmas, violent events or instabilities inject energy into turbulent motions at large scales. Nonlinear interactions among the turbulent fluctuations drive a cascade of energy to small perpendicular scales at which the energy is ultimately converted into plasma heat. Previous work with the incompressible magnetohydrodynamic (MHD) equations has shown that this turbulent energy cascade is driven by the nonlinear interaction between counterpropagating Alfven waves - also known as Alfven wave collisions. Direct numerical simulations of weakly collisional plasma turbulence enables deeper insight into the nature of the nonlinear interactions underlying the turbulent cascade of energy. In this paper, we directly compare four cases: both periodic and localized Alfven wave collisions in the weakly and strongly nonlinear limits. Our results reveal that in the more realistic case of localized Alfven wave collisions (rather than the periodic case), all nonlinearly generated fluctuations are Alfven waves, which mediates nonlinear energy transfer to smaller perpendicular scales.

19 pages, 7 figures

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• Electron acceleration from the interaction of three crossed parallel Alfvén waves
• Residual Energy and Broken Symmetry in Reduced Magnetohydrodynamics
• Initiation of Alfvénic turbulence by Alfven wave collisions: A numerical study