Kinetic theory of geomagnetic pulsations: 4. Hybrid gyrokinetic simulation of drift‐bounce resonant excitation of shear Alfvén waves
Kinetic theory of geomagnetic pulsations: 4. Hybrid gyrokinetic simulation of drift‐bounce resonant excitation of shear Alfvén waves
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DOI：
10.1029/2002ja009650
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发表时间：
2003-04
影响因子：
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通讯作者：
S. Dettrick;Linjin Zheng;Liu Chen
中科院分区：
文献类型：
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作者：
S. Dettrick;Linjin Zheng;Liu Chen
[1]利用一维线性混合旋动-磁流体动力学δf粒子模拟程序，研究了磁层环电流区高能粒子漂移-反弹共振Alfven模失稳的详细机制.模型等离子体是由一个冷（10- 100 eV）的组成部分，提供惯性加上一个微弱的能量（约10 keV）的“环电流”的组成部分，提供共振不稳定和压缩稳定的MHD模式。完整的动力学效应，如有限的拉莫尔半径和粒子磁反弹和进动漂移运动保留非微扰。假设了一个简单的有限β偶极平衡模型（β是等离子体压力和磁压力之比）。模拟结果与早期的微扰分析吻合良好。结果表明，当高能离子的热速度为超阿尔文时，离子通过漂移-反弹共振使奇偶剪切阿尔文MHD模失稳。由此产生的模式的增长率与等离子体β成线性比例。这些模式中最不稳定的是具有奇宇称的漂移-反弹共振不稳定模式，其波数使得赤道处的k <$ρ <$0.5（ρ是高能离子的拉莫尔半径）。不稳定通常发生在临界波数k ρ ≈ 0.3处。当波数接近这个临界值，等离子体β接近理想MHD临界值时，模频率由高能粒子动力学决定，类似于实验室聚变等离子体实验中观察到的高能粒子模（EPMs）。当高能粒子具有Alfvenic或亚Alfvenic热速度时，它们通过反弹共振对MHD模式起阻尼作用。
[1] A one-dimensional linear hybrid gyrokinetic-magnetohydrodynamic δf particle in cell simulation code is developed to study the detailed mechanisms of energetic particle drift-bounce resonant destabilization of Alfven modes in the ring-current region of the magnetosphere. The model plasma is composed of a cold (10–100eV) component which provides inertia plus a tenuous energetic (∼10 keV) “ring-current” component which provides both resonant destabilization and compressional stabilization of MHD modes. Full kinetic effects such as finite Larmor radii and particle magnetic bounce and precessional drift motions are retained nonperturbatively. A simple finite β dipolar equilibrium model is assumed (β is the ratio between plasma and magnetic pressures). Simulations show excellent agreement with earlier perturbative analyses. Results show that when the energetic ion thermal velocity is super-Alfvenic, the ions destabilize both odd and even parity shear Alfven MHD modes via the drift-bounce resonances. The growth rates of the resulting modes scale linearly with plasma β. The most unstable of these modes are found to be drift-bounce resonance destabilized modes with odd parity, with wave numbers such that k⟂ρ ≈ 0.5 at the equator (ρ is the energetic ion Larmor radius). The destabilization typically occurs at a critical wave number k⟂ρ ≈ 0.3. When the wave number is close to this critical value and the plasma β is close to the ideal MHD critical value, the mode frequency is determined by the energetic particle dynamics, similar to the energetic particle modes (EPMs) observed in laboratory fusion plasma experiments. When the energetic particles have Alfvenic or sub-Alfvenic thermal velocity, they contribute to damping of the MHD modes via the bounce resonance.