Gyroharmonic emissions induced by energetic ions in the equatorial plasmasphere
Gyroharmonic emissions induced by energetic ions in the equatorial plasmasphere
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DOI：
10.1029/ja084ia06p02597
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发表时间：
1979-06
影响因子：
--
通讯作者：
S. Curtis;C. Wu
中科院分区：
文献类型：
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作者：
S. Curtis;C. Wu
考虑了在地球等离子体层中观察到的热等离子体中高能离子 (E ≳ 0.1 MeV) 激发离子陀螺谐波静电和电磁波的一般问题。热等离子体被认为主要是 H+ 以及源自电离层的痕量较高 Z 离子成分，例如 He+ 和 O+。该等离子体成分具有麦克斯韦分布，支持Z≥1的高能离子激发的波。高能离子的能量具有幂律分布，具有很强的俯仰角各向异性。高能离子的自由能源与波的耦合是通过离子陀螺频率Ωα的速度依赖性获得的。由于自由能耦合、波放大和离子回旋加速器阻尼所施加的限制，发现紧密限制在磁赤道内的几乎垂直传播的快速磁声波的主要增长率。由于共振条件，生长被限制在紧邻离子陀螺谐波之下的频率，并且意味着线宽为 ∼ 10−3Ωα。发现快磁声波具有显着的电磁分量，该电磁分量随着陀螺谐波数的增加而减少。极化几乎完全变成静电，其中快速磁声波和离子伯恩斯坦分支在较低混合频率之上合并。当与离子陀螺谐波发射的观测结果进行比较时，该理论表明等离子体层中存在大量 Z ≳ 2 MeV 离子的电荷态。
The general problem of the excitation of ion gyroharmonic electrostatic and electromagnetic waves by energetic ions (E ≳ 0.1 MeV) in a thermal plasma as observed in the earth's plasmasphere is considered. The thermal plasma is taken to be predominantly H+ with trace higher Z ion constituents of ionospheric origin such as He+ and O+. This plasma component has a Maxwellian distribution and supports the waves which may be excited by energetic ions with Z ≳ 1. The energetic ions possess a power law distribution in energy with strong pitch angle anisotropy. Coupling of the free energy source of the energetic ions to the waves is obtained via the velocity dependence of the ion gyrofrequency Ωα. Owing to constraints imposed by free energy coupling, wave amplification, and ion cyclotron damping, the dominant growth rates are found for nearly perpendicularly propagating fast magnetosonic waves closely confined to the magnetic equator. Growth is restricted to frequencies immediately below the ion gyroharmonics by the resonance condition and implies line widths of ∼ 10−3Ωα. The fast magnetosonic waves are found to have a significant electromagnetic component which decreases with increasing gyroharmonic number. The polarization becomes almost entirely electrostatic where the fast magnetosonic and ion Bernstein branches merge above the lower hybrid frequency. When it is compared to observations of ion gyroharmonic emissions, the theory implies that there exist a significant number of charge states for Z ≳ 2 MeV ions in the plasmasphere.