太阳风可压缩Turbulence中的质子加热
Proton Heating in Solar Wind Compressible Turbulence with Collisions between Counter-propagating Waves
摘要：
磁流体湍流被认为在实验室、空间和天体物理等离子体加热中起着至关重要的作用。然而，湍流波动和颗粒动力学之间的精确联系尚未建立。在这里，我们提出了明确的证据等离子体湍流加热诊断波的特点和质子速度分布的基础上，从太阳风测量的风航天器。我们首次报道了在太阳风湍流中同时观测到反向传播的磁流体动力学波。与传统的Alfvén波反向传播的模式不同，在这种新型的太阳风可压缩湍流中，向阳慢磁声波（SMW）会遇到反向阳Alfvén波（AWs）。反向传播的AWs和SWs分别对应于不平衡Elsässer变量的优势和次优势种群。AWs和SMW之间的非线性相互作用推断从一个波的可能的振荡方向和其他的可能的传播方向之间的非正交性。相关的质子显示出双向不对称的光束在其速度分布：向阳光束出现在短而窄的模式和反向阳广泛的延长尾巴。这表明，多种类型的波粒相互作用，即，回旋加速器和朗道共振与AW和SMW在动力学尺度，正在发生联合加热质子垂直和平行。
英文摘要：
Magnetohydronamic turbulence is believed to play a crucial role in heating the laboratorial, space, and astrophysical plasmas. However, the precise connection between the turbulent fluctuations and the particle kinetics has not yet been established. Here we present clear evidence of plasma turbulence heating based on diagnosed wave features and proton velocity distributions from solar wind measurements by the Wind spacecraft. For the first time, we can report the simultaneous observation of counter-propagating magnetohydrodynamic waves in the solar wind turbulence. Different from the traditional paradigm with counter-propagating Alfvén waves, anti-sunward Alfvén waves (AWs) are encountered by sunward slow magnetosonic waves (SMWs) in this new type of solar wind compressible turbulence. The counter-propagating AWs and SWs correspond respectively to the dominant and sub-dominant populations of the imbalanced Elsässer variables. Nonlinear interactions between the AWs and SMWs are inferred from the non-orthogonality between the possible oscillation direction of one wave and the possible propagation direction of the other. The associated protons are revealed to exhibit bi-directional asymmetric beams in their velocity distributions: sunward beams appearing in short and narrow patterns and anti-sunward broad extended tails. It is suggested that multiple types of wave-particle interactions, i.e., cyclotron and Landau resonances with AWs and SMWs at kinetic scales, are taking place to jointly heat the protons perpendicularly and parallel.
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