发表机构
The University of Texas at Austin（德克萨斯大学奥斯汀分校）
机构由 AI 辅助整理，请以论文原文为准。AI 中文总结
该研究通过三维混合模拟对比平衡与不平衡阿尔文湍流，发现交叉 helicity 是控制无碰撞湍流等离子体大尺度演化、动力学活动和能量耗散的关键参数，平衡湍流的能量耗散与质子加热更显著。
AI 中文摘要
我们通过三维混合动力学模拟，研究了自由衰减的平衡与不平衡阿尔文湍流中从大尺度到亚质子尺度的湍流动态、动力学波活动以及由此产生的质子加热。我们考虑了初始涨落，其振幅和谱形相同，但速度与磁场扰动之间的相关程度（即归一化交叉 helicity）不同，这定义了相应的湍流 regime。我们发现，与不平衡情况相比，平衡湍流模拟表现出更强的能量耗散和更高效的质子加热。在大流体尺度上，两次模拟经历了不同的非线性动态和级联过程，一旦湍流充分发展，会导致不同的谱特性。在亚质子尺度上，涨落主要是斜向的，具有右旋极化，这是两种 regime 的共同特性。相比之下，只有不平衡模拟显示出与引导磁场平行的显著波功率，具有离子回旋波的清晰特征。这些波在阿尔文涨落初始非线性陡化过程中产生的强温度各向异性区域被激发，该过程同时产生平行传播的质子束。此外，速度空间中出现非麦克斯韦特征，表明平衡与不平衡 regime 中存在不同的加热机制，并为动力学不稳定性在调节湍流动态中的作用提供了证据。总体而言，这些结果表明，交叉 helicity 是控制无碰撞湍流等离子体中大尺度演化、动力学活动和能量耗散的关键参数。
英文摘要
We investigate turbulent dynamics from large to sub-proton scales, the kinetic wave activity and resulting proton heating in three-dimensional hybrid-kinetic simulations of freely decaying balanced and imbalanced Alfvénic turbulence. We considered initial fluctuations with same amplitude and spectral shape but different degrees of correlation between velocity and magnetic field perturbations (i.e., normalized cross-helicity), which define the corresponding turbulent regimes. We found that our balanced turbulence simulation exhibits stronger energy dissipation and more efficient proton heating compared to the imbalanced case. On the large fluid scales, the two simulations undergo distinct nonlinear dynamic and energy cascades, leading to different spectral properties once turbulence is well developed. At sub-proton scales, fluctuations are predominantly oblique with right-hand polarization, a property common to both regimes. In contrast, only the imbalanced simulation displays substantial wave power parallel to the guide magnetic field, with clear signatures of ion-cyclotron waves. These waves are excited in regions with strong temperature anisotropy that arise during the initial nonlinear steepening of Alfvénic fluctuations, a process that simultaneously generates parallel-propagating proton beams. Furthermore, non-Maxwellian features emerge in velocity space, indicating different heating mechanisms in balanced and imbalanced regimes and providing evidence for the role of kinetic instabilities in regulating the turbulent dynamics. Overall, these results show that cross-helicity is a key parameter controlling the large-scale evolution, kinetic activity, and energy dissipation in collisionless turbulent plasmas.
