在多流体描述下的日冕离子回旋加速器束不稳定性
Coronal ion-cyclotron beam instabilities within the multi-fluid description
摘要：
光谱观测和理论模型表明，共振波粒子相互作用，包括高频离子回旋波，作为加热和加速开放的冕洞离子的主要机制。然而，离子回旋波产生的机制仍不清楚。一种可能的情况是，源自小规模重联事件的离子束可以驱动构成离子回旋波激发的可能源的微不稳定性。为了研究离子束驱动的电磁不稳定性，采用了低β日冕等离子体中的多流体模型。在忽略电子惯性的同时，该模型允许考虑离子回旋波效应，这是单流体MHD模型所不存在的。本文利用真实的密度和温度模型以及2-D解析磁场模型来定义极冕洞开放场漏斗区的背景等离子体。考虑到WKB近似，傅立叶平面波线性模式分析，以推导色散关系。利用射线追迹理论计算了不稳定波在日冕漏斗中传播时的射线路径和增长率的演化。我们表明，在典型的冕洞条件下，假设现实的值的束速度，由平行的环境场传播的离子束提供的自由能可以驱动微不稳定性，通过共振离子回旋激发。
英文摘要：
Spectroscopic observations and theoretical models suggest resonant wave-particle interactions, involving high-frequency ion-cyclotron waves, as the principal mechanism for heating and accelerating ions in the open coronal holes. However, the mechanism responsible for the generation of the ion-cyclotron waves remains unclear. One possible scenario is that ion beams originating from small-scale reconnection events can drive micro-instabilities that constitute a possible source for the excitation of ion-cyclotron waves. In order to study ion beam-driven electromagnetic instabilities, the multi-fluid model in the low-beta coronal plasma is used. While neglecting the electron inertia this model allows one to take into account ion-cyclotron wave effects that are absent from the one-fluid MHD model. Realistic models of density and temperature as well as a 2-D analytical magnetic field model are used to define the background plasma in the open-field funnel region of a polar coronal hole. Considering the WKB approximation, a Fourier plane-wave linear mode analysis is employed in order to derive the dispersion relation. Ray-tracing theory is used to compute the ray path of the unstable wave as well as the evolution of the growth rate of the wave while propagating in the coronal funnel. We demonstrate that, in typical coronal holes conditions and assuming realistic values of the beam velocity, the free energy provided by the ion beam propagating parallel the ambient field can drive micro-instabilities through resonant ion-cyclotron excitation.
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