赤道电急流与极光电急流中的非麦克斯韦离子分布
Non-Maxwellian Ion Distribution in the Equatorial and Auroral Electrojets
AI总结：
针对电急流强电场导致的非麦克斯韦离子分布，本文用Boltzmann方程与BGK算子建立解析模型，并通过三维PIC模拟验证其能捕捉总体动量与能量流。
摘要：
极光电急流和赤道电急流中的强电场会使背景离子分布函数发生畸变，偏离麦克斯韦分布。我们利用Boltzmann方程和一个简单的BGK碰撞算子建立了碰撞等离子体动理学模型，该模型预测了背景电场强度与所得离子分布函数之间相对简单的关系。为检验该模型，我们开展了三维等离子体particle-in-cell（PIC，粒子在格）模拟，并将结果与模型进行比较。模拟采用弹性碰撞算子，并假设离子—中性粒子碰撞率为常数。这些模拟显示，Pedersen方向上的离子加热弱于解析模型，但总体加热情况相似。该模型高估Pedersen方向加热的原因在于，简单BGK算子在离子速度空间中不包含角碰撞散射。另一方面，全动理学particle-in-cell代码能够捕捉三维离子散射的物理过程，因此对离子的加热更具各向同性。尽管简单BGK解析理论不能精确描述非麦克斯韦离子分布函数，但它确实捕捉到了总体动量和能量流，因此可为进一步分析E区波的演化提供基础。
英文摘要：
Strong electric fields in the auroral and equatorial electrojets can distort the background ion distribution function away from Maxwellian. We developed a collisional plasma kinetic model using the Boltzmann equation and a simple BGK collision operator which predicts a relatively simple relationship between the intensity of the background electric field and the resulting ion distribution function. To test the model, we perform 3-D plasma particle-in-cell simulations and compare the results to the model. The simulation applies an elastic collision operator assuming a constant ion-neutral collision rate. These simulations show less ion heating in the Pedersen direction than the analytic model but show similar overall heating. The model overestimates the heating in the Pedersen direction because the simple BGK operator includes no angular collisional scattering in the ion velocity space. On the other hand, the fully-kinetic particle-in-cell code is able to capture the physics of ion scattering in 3-D and therefore heats ions more isotropically. Although the simple BGK analytic theory does not precisely model the non-Maxwellian ion distribution function, it does capture the overall momentum and energy flows and therefore can provide the basis of further analysis of E-region wave evolution.
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