临界平衡湍流中垂直离子加热的准线性理论
Quasi-linear theory of perpendicular ion heating by critically balanced turbulence
AI总结：
本文利用准线性理论，解析计算了离子与湍流大尺度阿尔芬涨落相互作用的加热率，揭示了湍流不平衡度如何使加热机制从随机加热平滑过渡到回旋共振加热，并得到了普适的加热率形式。
摘要：
在无碰撞天体物理等离子体中，湍流介导了自由能在级联通道间的分配及其耗散为离子和电子热。产生的离子加热通常是各向异性的，观测到离子优先垂直于局地磁场被加热；理解这种加热机制是理解此类等离子体演化的关键步骤。本文利用准线性理论框架，解析计算了离子与湍流大尺度阿尔芬涨落相互作用的加热率。我们展示了湍流的不平衡度（平行和反平行于磁场传播的阿尔芬涨落之间的能量差）如何修改这些涨落的时空谱，使得加热机制在平衡湍流中的随机加热和不平衡湍流中的回旋共振加热之间平滑过渡。得到的加热率具有与不平衡度无关的一般形式，在小湍流振幅下表现出与离子磁矩守恒相关的抑制，并在形式计算中恢复了先前的经验结果。本文的工作有助于巩固我们对天体物理等离子体中离子加热的定性理解，并为分析模拟和观测提供具体的定量预测。
英文摘要：
In collisionless astrophysical plasmas, turbulence mediates the partitioning of free energy among cascade channels and its dissipation into ion and electron heat. The resulting ion heating is often anisotropic, with ions observed to be preferentially heated perpendicular to the local magnetic field; understanding the mechanisms responsible for this heating is a key step in understanding the evolution of such plasmas. In this paper, we use the framework of quasi-linear theory to compute analytically the heating rates of ions interacting with turbulent, large-scale Alfvénic fluctuations. We show how the imbalance of the turbulence (the difference in energies between Alfvénic fluctuations travelling parallel and antiparallel to the magnetic field) modifies the spatiotemporal spectrum of these fluctuations, allowing the heating mechanism to smoothly transition between stochastic heating in balanced turbulence and cyclotron-resonant heating in imbalanced turbulence. The resultant heating rate is found to have a general form regardless of the level of imbalance, exhibiting a suppression related to the conservation of the ions' magnetic moment at small turbulent amplitudes and recovering previous empirical results in a formal calculation. The results of this work help to consolidate our qualitative understanding of ion heating within astrophysical plasmas, as well as yielding specific quantitative predictions to analyse simulations and observations.
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