Ion cyclotron instability due to the thermal anisotropy of drifting ion species
Ion cyclotron instability due to the thermal anisotropy of drifting ion species
复制标题
由于漂移离子种类的热各向异性而导致离子回旋不稳定性
DOI：
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发表时间：
2003
期刊：
影响因子：
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通讯作者：
J. Valdivia
中科院分区：
文献类型：
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作者：
L. Gomberoff;J. Valdivia
[i]在最近对氧离子的热各向异性产生的离子回旋波的研究中，表明重离子漂移速度和重离子的大的热各向异性可以使质子回旋波不稳定[Gomberoff和Valdivia，2003]。在这里，这项研究扩展到α粒子，以表明，一个小得多的热各向异性是需要触发强质子回旋波。它还表明，在某些条件下，α粒子分支的色散关系变得不稳定的频率值超过质子的回旋频率。这种不稳定性发生在非常大的α粒子热各向异性和非常低的β α= vth 2/vA 2，其中vth和vA分别是热和阿尔芬速度。色散关系的这个分支的最大增长率发生在α粒子的漂移速度大于驱动质子回旋不稳定性的最大增长率的α粒子。最后，它表明，氧离子和α粒子的联合作用导致一个复杂的不稳定谱，并加强质子回旋不稳定性。这种机制类似于级联效应，其中低频离子回旋波可以通过重离子的各向异性加热和加速来驱动不稳定的高频离子回旋波。这些结果可能与理解冕洞中快速太阳风的加热过程有关。
[i] In a recent study of ion cyclotron waves generated by the thermal anisotropy of oxygen ions, it was shown that the heavy ion drift velocity and a large thermal anisotropy of the heavy ions can destabilize proton-cyclotron waves [Gomberoff and Valdivia, 2003]. Here this study is extended to alpha particles in order to show that a much smaller thermal anisotropy is required to trigger strong proton-cyclotron waves. It is also shown that under some conditions, the alpha particle branch of the dispersion relation becomes unstable for frequency values beyond the proton gyrofrequency. This instability occurs for very large alpha particle thermal anisotropy and very low β∥α= v th 2/v A 2, where v th and v A are the thermal and Alfven velocity, respectively. The maximum growth rate of this branch of the dispersion relation occurs for drift velocities of the alpha particles larger than those that drive the maximum growth rate of the proton-cyclotron instability. Finally, it is demonstrated that the combined effect of oxygen ions and alpha particles lead to a complex unstable spectrum, and to an enhancement of the proton-cyclotron instability. This mechanism is like a cascade effect in which low-frequency ion cyclotron waves can drive unstable high-frequency ion cyclotron waves through anisotropic heating and acceleration of heavy ions. These results may be relevant to the understanding of the heating process of the fast solar wind in coronal holes.