Electron heating and energy inventory during asymmetric reconnection in a laboratory plasma
Electron heating and energy inventory during asymmetric reconnection in a laboratory plasma
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实验室等离子体不对称重联过程中的电子加热和能量库存
DOI：
10.1002/2017ja024152
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发表时间：
2017
期刊：
影响因子：
--
通讯作者：
Li‐Jen Chen
中科院分区：
文献类型：
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作者：
J. Yoo;B. Na;J. Jara;M. Yamada;H. Ji;V. Roytershteyn;M. Argall;W. Fox;Li‐Jen Chen
在实验室等离子体中研究了不对称重联期间的电子加热和能量库存，电流片上的密度比约为 8。观察到不对称重联的特征，例如低密度侧分离附近的大密度梯度、不对称面内电场和双极面外磁场。与对称情况不同，电子在低密度侧分离面附近也会被加热。测量的平行电场可以解释观察到的电子加热。尽管在低密度侧分离附近也观察到由较低混合漂移不稳定性驱动的大波动，但本文报告的实验室测量和数值模拟表明它们在电子赋能中不起主要作用。排气区域中的平均电子温度增加与每个电子/离子对的传入磁能成正比，但超过了先前空间观测的比例。这种差异可以通过边界条件和系统规模的差异来解释。电场的电子能量增益曲线表明，除了 X 线附近的大能量增益之外，还存在与电子反磁流相关的附加电子能量增益。这种额外的能量增益增加了电子的焓，而不是电子的温度。最后，对非对称重连期间的能量库存进行定量分析。与离子能量增益大约是电子能量增益两倍的对称情况不同，电子和离子在不对称重联期间获得相似的能量。
Electron heating and the energy inventory during asymmetric reconnection are studied in the laboratory plasma with a density ratio of about 8 across the current sheet. Features of asymmetric reconnection such as the large density gradients near the low‐density side separatrices, asymmetric in‐plane electric field, and bipolar out‐of‐plane magnetic field are observed. Unlike the symmetric case, electrons are also heated near the low‐density side separatrices. The measured parallel electric field may explain the observed electron heating. Although large fluctuations driven by lower hybrid drift instabilities are also observed near the low‐density side separatrices, laboratory measurements and numerical simulations reported here suggest that they do not play a major role in electron energization. The average electron temperature increase in the exhaust region is proportional to the incoming magnetic energy per an electron/ion pair but exceeds scalings of the previous space observations. This discrepancy is explained by differences in the boundary condition and system size. The profile of electron energy gain from the electric field shows that there is additional electron energy gain associated with the electron diamagnetic current besides a large energy gain near the X line. This additional energy gain increases electron enthalpy, not the electron temperature. Finally, a quantitative analysis of the energy inventory during asymmetric reconnection is conducted. Unlike the symmetric case where the ion energy gain is about twice more than the electron energy gain, electrons and ions obtain a similar amount of energy during asymmetric reconnection.