Two-dimensional (2D) test particle simulations based on shock profiles issued from 2D full particle-in-cell (PIC) simulations are used in order to analyze the formation processes of ions back streaming within the upstream region after interacting with a quasi-perpendicular curved shock front. Two different types of simulations have been performed based on (i) a fully consistent expansion (FCE) model, which includes all self-consistent shock profiles at different times, and (ii) a homothetic expansion (HE) model in which shock profiles are fixed at certain times and artificially expanded in space. The comparison of both configurations allows one to analyze the impact of the front nonstationarity on the back-streaming population. Moreover, the role of the space charge electric field E_l is analyzed by either including or canceling the E_l component in the simulations. A detailed comparison of these last two different configurations allows one to show that this E_l component plays a key role in the ion reflection process within the whole quasi-perpendicular propagation range. Simulations provide evidence that the different field-aligned beam (FAB) and gyro-phase bunched (GPB) populations observed in situ are essentially formed by a E_t×B drift in the velocity space involving the convective electric field E_t. Simultaneously, the study emphasizes (i) the essential action of the magnetic field component on the GPB population (i.e., mirror reflection) and (ii) the leading role of the convective field E_t in the FAB energy gain. In addition, the electrostatic field component E_l is essential for reflecting ions at high θ_Bn angles and, in particular, at the edge of the ion foreshock around 70^∘. Moreover, the HE model shows that the rate BI_% of back-streaming ions is strongly dependent on the shock front profile, which varies because of the shock front nonstationarity. In particular, reflected ions appear to escape periodically from the shock front as bursts with an occurrence time period associated to the self-reformation of the shock front.

中文翻译：

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借助测试粒子二维模拟深入了解离子前震

使用二维（2D）测试粒子模拟，该模拟基于2D全细胞模拟（PIC）模拟发出的冲击剖面，以便分析与准垂直相互作用后在上游区域内回流的离子的形成过程。弯曲的防震前板。基于（i）完全一致的膨胀（FCE）模型（包括在不同时间的所有自洽冲击轮廓）和（ii）冲击轮廓为的同质膨胀（HE）模型，执行了两种不同类型的仿真。在某些时间固定并人为地扩展空间。两种配置的比较使我们能够分析前不稳定对回流人口的影响。而且，空间电荷电场E _l的作用通过在仿真中包括或取消E _l分量来分析。对这最后两种不同配置的详细比较使我们可以证明，该E _l分量在整个准垂直传播范围内的离子反射过程中起着关键作用。模拟提供了证据，即在现场观察到的不同的场取向束（FAB）和陀螺相成束（GPB）种群基本上是由涉及对流电场E _t的速度空间中的E _t × B漂移形成的。同时，研究强调（i）磁场分量对GPB种群的基本作用（即镜面反射），以及（ii）对流场E _t在FAB能量获取中的主导作用。另外，静电场分量Ë_升是在高反射离子必不可少θ _BN角和，特别地，在离子的前震的周围的边缘70 ^∘。此外，HE模型显示出BI _％回流离子的离子强烈依赖于激波锋面，因为激波锋面的不稳定性，激波锋面的轮廓会有所不同。特别地，反射离子似乎以突发的形式从冲击锋面周期性地逸出，其发生时间段与冲击锋面的自重相关。