A collisional test-particle model of electrons at a comet
A collisional test-particle model of electrons at a comet
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彗星上电子的碰撞测试粒子模型
DOI：
10.1093/mnras/stac055
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发表时间：
2022
影响因子：
4.8
通讯作者：
Stephenson P
中科院分区：
文献类型：
--
作者：
Stephenson P
我们已经开发了第一个3D碰撞模型的电子在彗星，我们用它来检查电子中性碰撞的影响，在弱释气制度。测试粒子蒙特卡罗模型使用来自全动力学粒子单元（PiC）模型的电场和磁场作为输入。在我们的模型中，电子来源于太阳风或中性彗发的电离，无论是通过电子碰撞或吸收极紫外光子。所有相关的电子中性碰撞过程包括在模型中，包括弹性散射，激发和电离。电子的轨迹进行了验证，对分析已知的漂移和随机的能量退化模型中使用的连续减速近似进行比较。太阳风和彗星的电子种群的宏观特性，如密度和温度，验证与简单的已知情况下，并通过与碰撞PiC模型的比较。我们证明，电子被捕获的双极电场靠近原子核，导致电子中性碰撞的效率增加。即使在低释气率（Q= 1026s−1）下，电子与中性粒子的碰撞也会导致彗发的显著冷却。该模型还提供了一个多步数值框架，用于评估电子与离子质量比的影响，使访问电子动力学与物理电子质量。
We have developed the first 3D collisional model of electrons at a comet, which we use to examine the impact of electron-neutral collisions in the weakly outgassing regime. The test-particle Monte Carlo model uses electric and magnetic fields from a fully kinetic Particle-in-Cell (PiC) model as an input. In our model, electrons originate from the solar wind or from ionization of the neutral coma, either by electron impact or absorption of an extreme ultraviolet photon. All relevant electron-neutral collision processes are included in the model including elastic scattering, excitation, and ionization. Trajectories of electrons are validated against analytically known drifts and the stochastic energy degradation used in the model is compared to the continuous slowing down approximation. Macroscopic properties of the solar wind and cometary electron populations, such as density and temperature, are validated with simple known cases and via comparison with the collisionless PiC model. We demonstrate that electrons are trapped close to the nucleus by the ambipolar electric field, causing an increase in the efficiency of electron-neutral collisions. Even at a low-outgassing rate (Q= 1026s−1), electron-neutral collisions are shown to cause significant cooling in the coma. The model also provides a multistep numerical framework that is used to assess the influence of the electron-to-ion mass ratio, enabling access to electron dynamics with a physical electron mass.