定域强非线性阿尔芬波包碰撞中能量传递中介的阿尔芬性质
The Alfvenic nature of energy transfer mediation in localized, strongly nonlinear Alfven wavepacket collisions
摘要：
在空间和天体物理等离子体中，剧烈事件或不稳定性将能量注入大尺度的湍流运动。湍流波动之间的非线性相互作用将能量级联到小的垂直尺度，在该尺度下能量最终转化为等离子体热。以前的工作与不可压缩磁流体动力学（MHD）方程已经表明，这种湍流能量级联是由反向传播的阿尔芬波之间的非线性相互作用驱动的-也称为阿尔芬波碰撞。弱碰撞等离子体湍流的直接数值模拟，使更深入地了解湍流级联能量的非线性相互作用的本质。在本文中，我们直接比较了四种情况：在弱和强非线性极限下的周期和局域阿尔芬波碰撞。我们的研究结果表明，在更现实的情况下，本地阿尔芬波碰撞（而不是周期性的情况下），所有非线性产生的波动阿尔芬波，介导的非线性能量转移到较小的垂直尺度。
英文摘要：
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.
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