Motivated by recent observations of ‘electron-only’ magnetic reconnection, without an ion-scale sheet or ion outflows, in both the Earth’s magnetosheath and in numerical simulations, we study the formation and reconnection of electron-scale current sheets at low plasma $\unicode[STIX]{x1D6FD}$ . We first show that ideal sheets collapse to thicknesses much smaller than the ion scales, by deriving an appropriate analogue of the Chapman–Kendall collapse solution. Second, we show that, in practice, reconnection onset happens in these collapsing sheets once they reach a critical aspect ratio, because the tearing instability then becomes faster than their collapse time scale. We show that this can happen for sheet thicknesses larger than the ion scale or at only a few times the electron scale, depending on plasma parameters and the aspect ratio of the collapsing structure, thereby unifying the usual picture of ion-coupled reconnection and the new regime of electron-only reconnection. We derive relationships between plasma $\unicode[STIX]{x1D6FD}$ , ion-to-electron temperature ratio, the aspect ratio, electron outflow velocity and the final thickness of the sheets, and thus determine under what circumstances electron-scale sheets form and reconnect.

中文翻译：

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仅电子重联的开始

受最近在地球磁鞘和数值模拟中观察到的“仅电子”磁重联，没有离子尺度片或离子流出的启发，我们研究了低等离子体下电子尺度电流片的形成和重新连接 $\unicode[STIX]{x1D6FD}$ . 我们首先通过推导 Chapman-Kendall 塌陷解的适当类似物，证明理想的薄片塌陷到比离子尺度小得多的厚度。其次，我们表明，在实践中，一旦这些折叠片达到临界纵横比，重新连接就会发生，因为撕裂的不稳定性会变得比它们的折叠时间尺度更快。我们表明，这可能发生在大于离子尺度或仅几倍于电子尺度的片材厚度上，这取决于等离子体参数和塌陷结构的纵横比，从而统一了离子耦合重联的通常图像和新的仅电子重联机制。我们推导出等离子体之间的关系 $\unicode[STIX]{x1D6FD}$ ，离子与电子的温度比，纵横比，电子流出速度和薄片的最终厚度，从而确定电子尺度薄片在什么情况下形成和重新连接。