Demagnetization of transmitted electrons through a quasi-perpendicular collisionless shock
Demagnetization of transmitted electrons through a quasi-perpendicular collisionless shock
复制标题
通过准垂直无碰撞冲击对传输电子进行消磁
DOI：
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发表时间：
2003
期刊：
影响因子：
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通讯作者：
V. Krasnoselskikh
中科院分区：
文献类型：
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作者：
B. Lembége;P. Savoini;M. Balikhin;S. Walker;V. Krasnoselskikh
通过理论计算和计算机模拟的对比研究，分析了准垂直无碰撞冲击前电子退磁的物理过程。本文采用二维全粒子自洽代码对超临界状态下的激波进行了模拟。目前对坡道内磁场（L Br）和电场（L Er）空间宽度的统计表明，它们的比值R = L Er /L Br约为1；该值适合于使电子退磁并提供与绝热系数的偏差[Balikhin等人，1998]。为了验证这一理论期望，采用了两种互补的方法。首先，从“标记”自一致电子穿过激波斜坡的轨迹分析了全电子陀螺周期与磁陀螺周期的偏差。在这种情况下，充分考虑了激波前的非平稳和非均匀性效应。其次，当仅考虑沿冲击法向的宽度冲击的影响时，这种影响被去除并使用测试粒子模拟来确定电子退磁的强度。两种方法都证实退磁发生在斜坡的前半段，也就是说，透射电子看到的梯度dE lx /dx为正。使用测试粒子模拟进行的统计结果表明，即使在中等超临界马赫数下，坡道内也会形成明显数量的退磁电子，并且退磁电子/磁化电子的相对百分比根据激波锋面的非平稳行为（自我改造）而变化。
Physical processes responsible for the electron demagnetization within the front of a quasiperpendicular collisionless shock are analyzed via a comparative study between theoretical calculations and computer simulations. Herein, simulation results of a shock in supercritical regime are based on the use of a 2-D full particle self-consistent code. Present statistics on the spatial widths of the magnetic field (L Br) and electric field (L Er) within the ramp show that their ratio R = L Er /L Br is around 1; this value is appropriate to demagnetize electrons and to provide a resulting deviation from adiabaticity [Balikhin et al., 1998]. In order to verify this theoretical expectation, two complementary approaches are used. First, the deviation of the full electron gyroperiod from the magnetic gyroperiod is analyzed from the trajectories of 'marked' self-consistent electrons crossing the shock ramp. In such a case, nonstationary and nonuniformity effects of the shock front are fully involved. Second, such effects are removed and test particles simulations are used in order to determine the strength of electron demagnetization when effects of width shock along the shock normal are included only. Both approaches confirm that demagnetization takes place within the first half of the ramp, that is, where the gradient dE lx /dx seen by transmitted electrons is positive. Statistical results performed using test particles simulations show that a noticeable number of demagnetized electrons are formed within the ramp even for a moderate supercritical Mach number and that the relative percentage of demagnetized/magnetized electrons varies according to the nonstationary behavior of the shock front (self-reformation).