Hybrid-kinetic Simulations of Ion Heating in Alfvenic Turbulence
Hybrid-kinetic Simulations of Ion Heating in Alfvenic Turbulence
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DOI：
10.3847/1538-4357/ab20cc
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发表时间：
2019-07-01
影响因子：
4.9
通讯作者：
Quataert, Eliot
中科院分区：
文献类型：
--
作者：
Arzamasskiy, Lev;Kunz, Matthew W.;Quataert, Eliot
我们提出了与无碰撞近地太阳风相关的驱动阿尔文波湍流的三维混合动力学数值模拟。特别关注离子拉莫尔尺度附近发生的光谱转变以及优先垂直离子加热和平行分布函数中非热翼的起源。使用几种新颖的诊断方法表明，随着动能阿尔文波波动（构成亚离子拉莫尔湍流级联的大部分）达到接近离子回旋加速器频率，离子加热速率会增加。我们发现大约 75%-80% 的级联能量用于加热离子，这与近地太阳风大致一致。这种加热伴随着粒子激发率和分布函数中清晰的速度空间特征，包括垂直速度分布中的扁平核心和平行速度分布中的非麦克斯韦翼。后者归因于传播时间阻尼和垂直受热颗粒向平行方向的俯仰角散射。伴随这些特征的是，当场能转化为热能时，亚离子拉莫尔磁场波动的光谱指数变得陡峭，超过了标准的-2.8。这些预测可以通过近地太阳风的测量来检验。
We present three-dimensional, hybrid-kinetic numerical simulations of driven Alfven-wave turbulence of relevance to the collisionless near-Earth solar wind. Special attention is paid to the spectral transition that occurs near the ion-Larmor scale and to the origins of preferential perpendicular ion heating and of nonthermal wings in the parallel distribution function. Several novel diagnostics are used to show that the ion heating rate increases as the kineticAlfven-wave fluctuations, which comprise the majority of the sub-ion-Larmor turbulent cascade, attain near-ioncyclotron frequencies. We find that approximate to 75%-80% of the cascade energy goes into heating the ions, broadly consistent with the near-Earth solar wind. This heating is accompanied by clear velocity-space signatures in the particle energization rates and the distribution functions, including a flattened core in the perpendicular-velocity distribution and non-Maxwellian wings in the parallel-velocity distribution. The latter are attributed to transit-time damping and the pitch-angle scattering of perpendicularly heated particles into the parallel direction. Accompanying these features is a steepening of the spectral index of sub-ion-Larmor magnetic-field fluctuations beyond the canonical -2.8, as field energy is transferred to thermal energy. These predictions may be tested by measurements in the near-Earth solar wind.