论文标题
在有限厚度的倾斜冲击时电子注入理论
Theory of Electron Injection at Oblique Shock of Finite Thickness
论文作者
论文摘要
提出了一种在无碰撞冲击时生成宇宙射线电子的电子注射理论。我们考虑了最近提出的称为随机冲击漂移加速度（SSDA）的粒子加速度机制。我们发现，SSDA可以理解为有限厚度的倾斜冲击的扩散粒子加速机制。更具体地说，它是通过对具有与冲击厚度相当的特征扩散长度的颗粒的扩散 - 转向方程来描述的。另一方面，如果扩散长度比厚度长得多，则相同的方程式会产生标准DSA。尽管SSDA可以预测，通常，光谱指数比DSA陡峭，但对于低能电子加速度，它效率要高得多，并且有利于注射。注射阈值能量对应于两个不同方案之间的过渡能。如果在冲击周围的湍流量表由离子惯性长度确定，则它在典型的星际和行星际条件下为$ 0.1 \ text { - } 1 $ MEV。高$ m_ \ textrm {a} / \cosθ_{bn} $，其中$ m_ \ textrm {a} $和$θ_{bn} $是alfvén马赫号和震动倾斜。该理论表明，在高弹药的年轻超新星残留冲击中，将更容易地实现电子到超浮动能量的有效加速度，但是除非上游磁场在弱或中等冲击中，否则在上游磁场中却几乎是垂直于休克正常的。
A theory of electron injection into diffusive shock acceleration (DSA) for the generation of cosmic-ray electrons at collisionless shocks is presented. We consider a recently proposed particle acceleration mechanism called stochastic shock drift acceleration (SSDA). We find that SSDA may be understood as a diffusive particle acceleration mechanism at an oblique shock of finite thickness. More specifically, it is described by a solution to the diffusion-convection equation for particles with the characteristic diffusion length comparable to the shock thickness. On the other hand, the same equation yields the standard DSA if the diffusion length is much longer than the thickness. Although SSDA predicts, in general, a spectral index steeper than DSA, it is much more efficient for low-energy electron acceleration and is favorable for injection. The injection threshold energy corresponds to the transition energy between the two different regimes. It is of the order of $0.1\text{-}1$ MeV in typical interstellar and interplanetary conditions if the dissipation scale of turbulence around the shock is determined by the ion inertial length. The electron injection is more efficient at high $M_\textrm{A} / \cos θ_{Bn}$ where $M_\textrm{A}$ and $θ_{Bn}$ are the Alfvén Mach number and the shock obliquity. The theory suggests that efficient acceleration of electrons to ultra-relativistic energies will be more easily realized at high-Mach-number young supernova remnant shocks, but not at weak or moderate shocks in the heliosphere unless the upstream magnetic field is nearly perpendicular to the shock normal.
