Collisionless transport of energetic electrons in the solar corona at current-free double layers
Collisionless transport of energetic electrons in the solar corona at current-free double layers
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DOI：
10.1051/0004-6361:20078419
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发表时间：
2008-02
影响因子：
6.5
通讯作者：
Kuang-Wu Lee;J. Büchner;N. Elkina
中科院分区：
文献类型：
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作者：
Kuang-Wu Lee;J. Büchner;N. Elkina
上下文撞击太阳色球层的电子束通过碰撞韧致辐射厚靶模型产生硬X射线辐射（HXR）。推导出的电子分布通常表现出破幂律。假设初始分布函数是一个漂移麦克斯韦，这表明高能电子的分布变化，在他们的传播过程中，从looptop加速网站的高密度色球，通过碰撞散射机制。目标。反向电流束等离子体系统中粒子与无电流弱双电层相互作用产生破幂律谱。方法.本文首先用线性不稳定性分析方法研究了无电流日冕等离子体中产生的不稳定波。对于最可能的日冕等离子体参数，进行一维静电Vlasov代码模拟，以了解非线性演化的不稳定性及其对电子分布的影响。结果DL结构导致低能束电子的耗散和返回电流电子的停滞。快速电子空穴形成，二次双流不稳定性，由DL加速电子引起。电子和离子加热的DL也发生。结论.日冕中高能电子的等离子体分布是通过与非线性大振幅相空间结构的相互作用而演化的。在演化的后期，低能电子被减慢，而高能量部分在DLs出现后不受影响。返回电流电子的主要部分改变其方向的注入束。因此，分布成为一个破幂律所观察到的色球HXR辐射。
Context. Impinging electron beams in the solar chromosphere generate hard X-ray radiation (HXR) through the collisional Bremstrahlung thick target model. The deduced electron distributions usually exhibit a broken-power-law. Assuming that the initial distribution function was a drift-Maxwellian, this indicates that the distribution of energetic electrons changes in the course of their propagation, from the looptop acceleration site to the high density chromosphere, via a collisionless scattering mechanism. Aims. The formation of a broken-power-law spectrum via the particle interaction with the current-free weak double layers (DLs) in a reverse current beam plasma system. Methods. The unstable waves generated in current-free coronal plasmas are first studied by means of a linear instability analysis. For most probable coronal plasma parameters, a one-dimensional electrostatic Vlasov-code simulation is performed to understand the nonlinear evolution of the instabilities and their influences on the electron distribution. Results. DL structures cause a dissipation of low energy beam electrons and a stagnation of return-current electrons. Fast electron holes are formed, a secondary two-stream instability, caused by the DL-accelerated electrons. Electron and ion heating by DLs also takes place. Conclusions. The plasma distributions of energetic electrons in the solar corona evolve via their interactions with nonlinear largeamplitude phase-space structures. At the late stage of evolution, the low-energy electrons are slowed down while the high energy part stays uninfluenced after the appearance of DLs. A major part of the return-current electrons change their direction to that of the injected beam. As a result the distribution becomes a broken-power-law as observed by chromospheric HXR radiation.