arXiv 2104.001732021-04-02astro-ph.SRastro-ph.GAphysics.plasm-ph

热压力对无碰撞磁重联率的影响

The Effect of Thermal Pressure on Collisionless Magnetic Reconnection Rate

Xiaocan Li, Yi-Hsin Liu

备注：: 19 pages, 7 figures, accepted for publication in ApJ
DOI：: 10.3847/1538-4357/abf48c

摘要：

无碰撞磁重联率的模拟是等离子体物理基础研究中的一个突出挑战。虽然在低$β$方案中经常报告$\mathcal{O}(0.1)$顺序的看似普遍的比率，但尚不清楚重新连接率如何与较高的血浆$β$成比例。由于压力张量的复杂性，现有的重连率模型仅限于低等离子体- $β$制度，其中的热压力可以忽略不计。然而，当$β\gtrsim \mathcal{O}(1)$。使用第一性原理动力学模拟，我们表明，随着$β$变大，重联率和流出速度都下降。考虑到扩散区周围力平衡中自生压力各向异性和压力梯度的影响，导出了一个简单的分析框架，解释了不同$β$条件下模拟中关键量和重联率的变化趋势.标准化重连率的预测比例是$β$上限中的$\simeq \mathcal{O}(0.1/\sqrt{β_{i0}})$，其中$β_{i0}$是流入血浆的离子$β$。

英文摘要：

Modeling collisionless magnetic reconnection rate is an outstanding challenge in basic plasma physics research. While the seemingly universal rate of an order $\mathcal{O}(0.1)$ is often reported in the low-$β$ regime, it is not clear how reconnection rate scales with a higher plasma $β$. Due to the complexity of the pressure tensor, the available reconnection rate model is limited to the low plasma-$β$ regime, where the thermal pressure is arguably negligible. However, the thermal pressure effect becomes important when $β\gtrsim \mathcal{O}(1)$. Using first-principle kinetic simulations, we show that both the reconnection rate and outflow speed drop as $β$ gets larger. A simple analytical framework is derived to take account of the self-generated pressure anisotropy and pressure gradient in the force-balance around the diffusion region, explaining the varying trend of key quantities and reconnection rates in these simulations with different $β$. The predicted scaling of the normalized reconnection rate is $\simeq \mathcal{O}(0.1/\sqrt{β_{i0}})$ in the high $β$ limit, where $β_{i0}$ is the ion $β$ of the inflow plasma.

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