Microturbulence in the electron cyclotron frequency range at perpendicular supercritical shocks
Microturbulence in the electron cyclotron frequency range at perpendicular supercritical shocks
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DOI：
10.1002/jgra.50224
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发表时间：
2013-05
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影响因子：
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通讯作者：
L. Muschietti;L. Muschietti;B. Lembége
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文献类型：
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作者：
L. Muschietti;L. Muschietti;B. Lembége
超临界垂直无碰撞冲击的特征在于入射离子的一小部分在陡峭的前沿被反射。这些反射的离子积累并形成一个脚，其中反射的离子束相对于电子的相对漂移可以容易地激发电子回旋漂移不稳定性（ECDI）。在这里，我们分析了两种方法产生的波发射。首先，我们的线性色散分析表明，几个电子伯恩斯坦谐波可以是不稳定的，它们的数量成正比的漂移，但由离子束温度的限制。其次，三个本地人口（入射电子/离子和反射离子）的脚区域被引入到全电磁粒子在细胞（PIC）周期性模拟，以分析ECDI的非线性制度。主要结果如下：（1）高回旋谐波在小于低杂波周期的短时间尺度内发展。(2)在两个互补过程的影响下，光谱功率向低k模式移动以在第一谐波上积累：（i）反射离子束的捕获和（ii）共振加宽。后者的作用是使色散关系中的电子退磁。它最初适用于非常高的k模式（kρe>>1），随着时间的推移，逐渐适用于较低的k模式，除了第一个之外，所有的回转谐波都不存在。(3)在后期阶段，磁场成分令人惊讶地在迄今为止一直是静电的能谱中发展出来。(4)电子被加热，这代表了冲击波阵面底部区域的预热源。
Supercritical perpendicular collisionless shocks are characterized by a fraction of the incoming ions being reflected at the steep front. These reflected ions accumulate and form a foot, where the relative drift of the reflected ion beam versus the electrons can easily excite an electron cyclotron drift instability (ECDI). Here, we analyze the resulting wave emissions by two approaches. First, our linear dispersion analysis shows that several electron Bernstein harmonics can be unstable, their number being proportional to the drift, yet limited by the ion beam temperature. Second, the three local populations (incoming electrons/ions and reflected ions) of the foot region are introduced in full electromagnetic particle‐in‐cell (PIC) periodic simulations in order to analyze the nonlinear regime of the ECDI. The main results are the following: (1) High gyroharmonics develop over a short time scale less than the lower hybrid period. (2) The spectral power shifts toward lower k modes to accumulate on the first harmonic under the effects of two complementary processes: (i) trapping of the reflected ion beam and (ii) resonance broadening. The latter acts to demagnetize the electrons in the dispersion relation. It initially applies to very high k modes (kρe>>1) and progressively, as time evolves, to lower k modes, invalidating the existence of all gyroharmonics except the first one. (3) In the late stage, a magnetic field component surprisingly develops in the energy spectrum that had so far been electrostatic. (4) The electrons are heated, which represents a source of preheating in the foot region of the shock front.