arXiv 2102.096542021-02astro-ph.SRphysics.plasm-phphysics.space-ph

低$β$动力学turbulence中的随机加热及其相空间特征

On stochastic heating and its phase-space signatures in low-$β$ kinetic turbulence

Silvio Sergio Cerri, Lev Arzamasskiy, Matthew W. Kunz

备注：: 23 pages, 9 figures (and 20 footnotes); accepted for publication in The Astrophysical Journal
DOI：: 10.3847/1538-4357/abfbde

摘要：

我们重新审视离子随机加热的理论，并研究其相空间签名动力学湍流的相关性低- $β$部分的太阳风。我们保留一个完整的规模依赖的方法在我们的治疗，并考虑的情况下，电场波动可以描述的广义欧姆定律，包括霍尔和热电效应。当离子拉莫尔尺度远小于离子趋肤深度$ρ_{\mathrm{i}}\ll d_{\mathrm{i}}$时，这两个电场项对随机离子加热起主导作用，这是$β{\ll}1$的情况。利用Alfvén波和动力学Alfvén波湍流涨落的谱标度律，我们得到了表征这两个区域中与随机加热相关的场垂直粒子扩散率和能量扩散系数的标度关系。离子加热的相空间签名，然后使用连续驱动Alfvénic湍流在低$β$的三维混合动力学模拟研究。在这些模拟中，平行于磁场的离子的湍流与其垂直对应物（$Q_{\parallel,\mathrm{i}}\ll Q_{\perp,\mathrm{i}}$）相比是次主导的，并且进入离子加热的湍流能量的分数在$β_{\mathrm{i}}=0.3$处为${\approx}75$，在$β_{\mathrm{i}}{\simeq}0.1$处为${\approx}40$。离子回旋的相空间特征与朗道共振无碰撞阻尼和离子回旋和随机加热的（$β$依赖）组合是一致的。我们证明了我们的理论和各种签名与随机部分的加热之间的良好协议。我们讨论的随机加热和我们的工作的影响，随机加热的太阳风航天器数据的解释不稳定性的影响。

英文摘要：

We revisit the theory of stochastic heating of ions and investigate its phase-space signatures in kinetic turbulence of relevance to low-$β$ portions of the solar wind. We retain a full scale-dependent approach in our treatment, and consider the case in which electric-field fluctuations can be described by a generalized Ohm's law that includes Hall and thermo-electric effects. These two electric-field terms provide the dominant contributions to stochastic ion heating when the ion-Larmor scale is much smaller than the ion skin depth, $ρ_{\mathrm{i}}\ll d_{\mathrm{i}}$, which is the case at $β{\ll}1$. Employing well-known spectral scaling laws for Alfvén-wave and kinetic-Alfvén-wave turbulent fluctuations, we obtain scaling relations characterizing the field-perpendicular particle-energization rate and energy diffusion coefficient associated with stochastic heating in these two regimes. Phase-space signatures of ion heating are then investigated using 3D hybrid-kinetic simulations of continuously driven Alfvénic turbulence at low $β$. In these simulations, energization of ions parallel to the magnetic field is sub-dominant compared to its perpendicular counterpart ($Q_{\parallel,\mathrm{i}}\ll Q_{\perp,\mathrm{i}}$), and the fraction of turbulent energy that goes into ion heating is ${\approx}75$\% at $β_{\mathrm{i}}=0.3$ and ${\approx}40$\% at $β_{\mathrm{i}}{\simeq}0.1$. The phase-space signatures of ion energization are consistent with Landau-resonant collisionless damping and a ($β$-dependent) combination of ion-cyclotron and stochastic heating. We demonstrate good agreement between our theory and various signatures associated with the stochastic portion of the heating. We discuss the effect of intermittency on stochastic heating and the implications of our work for the interpretation of stochastic heating in solar-wind spacecraft data.

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