Adaptive Critical Balance and Firehose Instability in an Expanding, Turbulent, Collisionless Plasma
Adaptive Critical Balance and Firehose Instability in an Expanding, Turbulent, Collisionless Plasma
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膨胀、湍流、无碰撞等离子体中的自适应临界平衡和消防水带不稳定性
DOI：
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发表时间：
2021
影响因子：
7.9
通讯作者：
J. Squire
中科院分区：
文献类型：
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作者：
A. Bott;L. Arzamasskiy;M. Kunz;E. Quataert;J. Squire
利用混合动力学粒子模拟，我们研究了膨胀的，无碰撞的，磁化等离子体中的强Alfvénic湍流持续驱动的演变。由等离子体膨胀产生的温度各向异性（以及随之而来的平均磁场强度的降低）逐渐降低了场线的有效弹性，导致阿尔夫维尼克波动的线性频率和剩余能量的降低。作为响应，这些波动修改它们的相互作用和空间各向异性，以保持它们的特征线性和非线性频率之间的逐尺度“临界平衡”。最终，等离子体变得不稳定，变成动力学消防水龙带不稳定性，从而激发离子拉莫尔尺度上快速增长的磁波动。随之而来的粒子的俯仰角散射保持边缘稳定附近的温度各向异性，即使作为湍流等离子体继续扩大。由此产生的平行和垂直温度的演变不满足双绝热守恒定律，但准确地描述了一个简单的模型，包括异常散射。我们的研究结果有影响，了解宏观和微观尺度的物理学之间的复杂的相互作用，在各种热，稀，天体物理等离子体，并提供预测功率谱，剩余能量，离子拉莫尔尺度的光谱断裂，和非麦克斯韦功能的离子分布函数，可以通过在太阳风的高β区域进行测量进行测试。
Using a hybrid-kinetic particle-in-cell simulation, we study the evolution of an expanding, collisionless, magnetized plasma in which strong Alfvénic turbulence is persistently driven. Temperature anisotropy generated adiabatically by the plasma expansion (and consequent decrease in the mean magnetic-field strength) gradually reduces the effective elasticity of the field lines, causing reductions in the linear frequency and residual energy of the Alfvénic fluctuations. In response, these fluctuations modify their interactions and spatial anisotropy to maintain a scale-by-scale “critical balance” between their characteristic linear and nonlinear frequencies. Eventually the plasma becomes unstable to kinetic firehose instabilities, which excite rapidly growing magnetic fluctuations at ion-Larmor scales. The consequent pitch-angle scattering of particles maintains the temperature anisotropy near marginal stability, even as the turbulent plasma continues to expand. The resulting evolution of parallel and perpendicular temperatures does not satisfy double-adiabatic conservation laws, but is described accurately by a simple model that includes anomalous scattering. Our results have implications for understanding the complex interplay between macro- and microscale physics in various hot, dilute, astrophysical plasmas, and offer predictions concerning power spectra, residual energy, ion-Larmor-scale spectral breaks, and non-Maxwellian features in ion distribution functions that may be tested by measurements taken in high-beta regions of the solar wind.
影响因子：
4.9
作者：
Arzamasskiy, Lev;Kunz, Matthew W.;Quataert, Eliot
通讯作者：
Quataert, Eliot