论文标题
电子预换I：电子声波的前加速器
Pre-acceleration in the Electron Foreshock I: Electron Acoustic Waves
论文作者
论文摘要
为了经历扩散的冲击加速度，需要预先加速电子以增加其能量的数量级，否则它们的陀螺仪比电击的有限宽度小。在倾斜的冲击中，上游磁场方向既不平行也不垂直于冲击正常，电子可以逃到上游的冲击，从而将冲击脚修改为称为电子预壳的区域。为了确定该区域的前加速度，我们在改变倾斜和平面角度的同时进行了倾斜冲击的PIC模拟。我们表明，尽管反射电子的比例可以忽略不计，而对于$θ_ {\ rm bn} = 74.3^\ circ $，但它增加到$ r \ sim 5 \％$ for $θ_ {\ rm bn} = 30^\ circ $，并通过这些电源来启动电动机，并通过电动启动电源，并通过电动驱动器来进行电动，并将其付诸实用。 $ r^{0.6} $和波长$ \大约2λ_{\ rm {se}}} $，其中$λ_{\ rm {se}} $是电子皮肤长度。虽然初始反射机制通常是冲击加速度和磁性镜像的组合，但我们表明，一旦在上游产生了静电波，它们本身就可以增加与磁场平行的上游电子的动量。在$ \ Lessim 1 \％的案例中，上游电子过早地远离冲击，而从未向下游注射。相比之下，类似的部分在反射后重新降低了冲击，重新交织的能量比热力大得多，然后越过下游。
To undergo diffusive shock acceleration, electrons need to be pre-accelerated to increase their energies by several orders of magnitude, else their gyro-radii are smaller than the finite width of the shock. In oblique shocks, where the upstream magnetic field orientation is neither parallel or perpendicular to the shock normal, electrons can escape to the shock upstream, modifying the shock foot to a region called the electron foreshock. To determine the pre-acceleration in this region, we undertake PIC simulations of oblique shocks while varying the obliquity and in-plane angles. We show that while the proportion of reflected electrons is negligible for $θ_{\rm Bn} = 74.3^\circ$, it increases to $R \sim 5\%$ for $θ_{\rm Bn} = 30^\circ$, and that, via the electron acoustic instability, these electrons power electrostatic waves upstream with energy density proportional to $R^{0.6}$ and a wavelength $\approx 2 λ_{\rm{se}}$, where $λ_{\rm{se}}$ is the electron skin length. While the initial reflection mechanism is typically a combination of shock surfing acceleration and magnetic mirroring, we show that once the electrostatic waves have been generated upstream they themselves can increase the momenta of upstream electrons parallel to the magnetic field. In $\lesssim 1\%$ of cases, upstream electrons are prematurely turned away from the shock and never injected downstream. In contrast, a similar fraction are re-scattered back towards the shock after reflection, re-interact with the shock with energies much greater than thermal, and cross into the downstream.
