Institute of Space Physics and Applied Technology, Peking University, Beijing, China.
Key laboratory of solar activity and space weather, National Space Science Center, Chinese Academy of Sciences, Beijing, China.
Nat Commun. 2023 Apr 12;14(1):2088. doi: 10.1038/s41467-023-37881-3.
Kinetic Alfvén waves (KAWs) are ubiquitous throughout the plasma universe. Although they are broadly believed to provide a potential approach for energy exchange between electromagnetic fields and plasma particles, neither the detail nor the efficiency of the interactions has been well-determined yet. The primary difficulty has been the paucity of knowledge of KAWs' spatial structure in observation. Here, we apply a particle-sounding technique to Magnetospheric Multiscale mission data to quantitatively determine the perpendicular wavelength of KAWs from ion gyrophase-distribution observations. Our results show that KAWs' perpendicular wavelength is statistically 2.4[Formula: see text] times proton thermal gyro-radius. This observation yields an upper bound of the energy the majority proton population can reach in coherent interactions with KAWs, that is, roughly 5.76 times proton perpendicular thermal energy. Therefore, the method and results shown here provide a basis for unraveling the effects of KAWs in dissipating energy and accelerating particles in a number of astrophysical systems, e.g., planetary magnetosphere, astrophysical shocks, stellar corona and wind, and the interstellar medium.
动理学阿尔芬波（KAW）在整个等离子体宇宙中无处不在。尽管人们普遍认为它们为电磁场和等离子体粒子之间的能量交换提供了一种潜在的途径，但相互作用的细节和效率尚未得到很好的确定。主要的困难是观测中对 KAW 空间结构的了解甚少。在这里，我们应用粒子探测技术对磁层多尺度任务数据进行分析，从离子回旋相位分布观测中定量确定 KAW 的垂直波长。我们的结果表明，KAW 的垂直波长在统计上是质子热回旋半径的 2.4[Formula: see text]倍。这一观测结果给出了大多数质子在与 KAW 相干相互作用中能够达到的能量上限，即质子垂直热能的约 5.76 倍。因此，这里展示的方法和结果为揭示 KAW 在多种天体物理系统中耗散能量和加速粒子的作用提供了基础，例如行星磁层、天体物理激波、恒星日冕和恒星风以及星际介质。
