Cluster observations of kinetic structures and electron acceleration within a dynamic plasma bubble
Cluster observations of kinetic structures and electron acceleration within a dynamic plasma bubble
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DOI：
10.1029/2012ja018323
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发表时间：
2013-02
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通讯作者：
Meng Zhou;Xiaohua Deng;M. Ashour‐Abdalla;R. Walker;Y. Pang;C. Tang;Shiyong Huang;M. El‐Alaoui-M.-El‐Alao
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文献类型：
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作者：
Meng Zhou;Xiaohua Deng;M. Ashour‐Abdalla;R. Walker;Y. Pang;C. Tang;Shiyong Huang;M. El‐Alaoui-M.-El‐Alao
在磁层亚暴等活动期，快速等离子体流被认为在磁尾的质量、动量和能量的传输中起着重要作用。本文给出了近地尾部X=−18RE亚暴爆发前与快速等离子体流有关的等离子体耗尽通量管的星系团观测结果。气泡由两条锋利的前导(∂BZ/∂x 0)边限定。两个边缘是薄电流层(大约离子惯性长度)，它不仅携带着强烈的垂直电流，而且还携带着场向电流。前缘是慢等离子体流中的偶极前沿(DF)，后缘嵌入超Alfvénic对流离子射流中。电子的喷射速度超过了离子的流动速度，因此在后缘产生了很大的切向电流。电子漂移主要由E×B漂移给出。有趣的是，后缘的移动速度快于前缘，这会导致气泡的收缩和气泡内部的局部通量堆积。这导致了BZ的进一步加剧，或二次双极化。前缘和后缘都是将电子限制在气泡内的切向不连续。强电子加速对应于二次偶极，垂直方向的电子通量占主导地位。我们认为，电子的能化是由倍他电子加速引起的。在气泡内部发现了呼啸波和较低的混合漂移波。讨论了它们的产生机制和在电子动力学中的潜在作用。
Fast plasma flows are believed to play important roles in transporting mass, momentum, and energy in the magnetotail during active periods, such as the magnetospheric substorms. In this paper, we present Cluster observations of a plasma‐depleted flux tube, i.e., a plasma bubble associated with fast plasma flow before the onset of a substorm in the near‐Earth tail around X = −18 RE. The bubble is bounded by both sharp leading (∂bz/∂x 0) edges. The two edges are thin current layers (approximately ion inertial length) that carry not only intense perpendicular current but also field‐aligned current. The leading edge is a dipolarization front (DF) within a slow plasma flow, while the trailing edge is embedded in a super‐Alfvénic convective ion jet. The electron jet speed exceeds the ion flow speed thus producing a large tangential current at the trailing edge. The electron drift is primarily given by the E × B drift. Interestingly, the trailing edge moves faster than the leading edge, which causes shrinking of the bubble and local flux pileup inside the bubble. This resulted in a further intensification of Bz, or a secondary dipolarization. Both the leading and trailing edges are tangential discontinuities that confine the electrons inside the bubble. Strong electron acceleration occurred corresponding to the secondary dipolarization, with perpendicular fluxes dominating the field‐aligned fluxes. We suggest that betatron acceleration is responsible for the electron energization. Whistler waves and lower hybrid drift waves were identified inside the bubble. Their generation mechanisms and potential roles in electron dynamics are discussed.