The interplay of Kappa and core populations in the solar wind: Electromagnetic electron cyclotron instability
The interplay of Kappa and core populations in the solar wind: Electromagnetic electron cyclotron instability
复制标题
太阳风中卡帕和核心粒子群的相互作用：电磁电子回旋不稳定性
DOI：
10.1002/2014ja020668
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发表时间：
2014
期刊：
影响因子：
--
通讯作者：
R. Schlickeiser
中科院分区：
文献类型：
--
作者：
M. Lazar;S. Poedts;R. Schlickeiser
最近，提出了一个现实的参数化的动力学各向异性和由此产生的不稳定性的太阳风等离子体。这种参数化是基于观测的粒子速度分布，它总是包括一个麦克斯韦人口在低能量，即核心，和一个超热晕在尾部的分布，这是最好的描述卡帕（幂律）模型。由各向异性电子晕驱动的回旋不稳定性被发现被核心中的有限热扩散抑制，并且这种效应高度依赖于晕-核心的相对密度。在本文中，卡帕和麦克斯韦人口之间的相互作用进一步研究更复杂（不太理想化）的情况下，核心和晕温度各向异性。这种不稳定性的增长显着刺激的核心各向异性。波数是稳定的各向同性核心变得不稳定，即使是小的各向异性的人口。芯部各向异性从Ac=T/T =1.2增加到2，仅引起增长率增加1个数量级，并且不稳定波数的范围显著扩展。当在核心和晕的各向异性是可比的，增长率表现出两个不同的峰值，第一个驱动的晕在较低的波数和第二个驱动的核心。然而，第一个峰值被抑制的超温人口，而第二个峰值是持续的，这表明一个更复杂的核心和卡帕人口之间的联系。
Recently, a realistic parameterization was proposed for the kinetic anisotropy and the resulting instabilities in the solar wind plasma. This parameterization is based on observations of the particle velocity distribution, which always comprises a Maxwellian population at low energies, viz. the core, and a suprathermal halo in the tail of the distribution which is best described by the Kappa (power law) models. The cyclotron instability, driven by an anisotropic electron halo, was found to be inhibited by the finite thermal spread in the core, and this effect is highly dependent on the halo‐core relative density. In this paper, the interplay between the Kappa and Maxwellian populations is further investigated for more complex (less idealized) situations when both the core and halo temperatures are anisotropic. Growth of this instability is markedly stimulated by the core anisotropy. The wave numbers that are stable for an isotropic core become unstable even for small anisotropies of this population. Just a modest increase of the core anisotropy from Ac=T⊥/T∥=1.2 to 2 causes the growth rates to enhance by 1 order of magnitude, and the range of unstable wave numbers to extend considerably. When the anisotropies in the core and halo are comparable, the growth rate exhibits two distinct peaks, the first driven by the halo at lower wave numbers and the second driven by the core. However, the first peak is inhibited by the suprathermal populations, while the second peak is sustained, suggesting a more intricate connection between the core and Kappa populations.