Non-thermal electron acceleration from magnetically driven reconnection in a laboratory plasma
Non-thermal electron acceleration from magnetically driven reconnection in a laboratory plasma
复制标题
DOI：
10.1038/s41567-022-01839-x
复制
发表时间：
2022-01
期刊：
影响因子：
19.6
通讯作者：
A. Chien;Lan Gao;Shu Zhang;H. Ji;E. Blackman;W. Daughton;A. Stanier;A. Le;F. Guo;R. Follett;Hui-Hwa Chen;G. Fiksel;G. Bleotu;R. Cauble;Sophia N Chen;A. Fazzini;K. Flippo;Omar French;D. Froula;J. Fuchs;S. Fujioka;K. Hill;S. Klein;C. Kuranz;P. Nilson;A. Rasmus;R. Takizawa
中科院分区：
文献类型：
--
作者：
A. Chien;Lan Gao;Shu Zhang;H. Ji;E. Blackman;W. Daughton;A. Stanier;A. Le;F. Guo;R. Follett;Hui-Hwa Chen;G. Fiksel;G. Bleotu;R. Cauble;Sophia N Chen;A. Fazzini;K. Flippo;Omar French;D. Froula;J. Fuchs;S. Fujioka;K. Hill;S. Klein;C. Kuranz;P. Nilson;A. Rasmus;R. Takizawa
磁重联能迅速将磁能转化为等离子体流动能、热能和非热能粒子的某种组合。在不同的无碰撞和低β环境下，人们已经从理论上提出了各种重联加速机制，并对其进行了数值研究，其中β指的是等离子体与磁压之比。这些机制包括费米加速、倍电子加速、沿磁场平行电场加速和重联电场直接加速。然而，它们都没有得到实验上的证实，因为在实验室实验中直接观测非热粒子加速是困难的，因为原位测量的德拜长度较短，非原位测量的平均自由程较短。本文报道了利用激光驱动的电容线圈平台在低β条件下直接测量磁驱重联产生的加速非热电子。我们使用千焦耳激光驱动平行电流，在准轴对称几何结构中重新连接兆高斯级磁场。测量的电子能谱和由此产生的加速能的角度依赖关系，并得到了粒子模拟的支持，表明面外重联电场对直接电场的加速机制是起作用的。使用这种机制的定标能量显示出与天体物理观测的直接关联。
Magnetic reconnection rapidly converts magnetic energy into some combination of plasma flow energy, thermal energy and non-thermal energetic particles. Various reconnection acceleration mechanisms have been theoretically proposed and numerically studied in different collisionless and low-βenvironments, whereβrefers to the plasma-to-magnetic pressure ratio. These mechanisms include Fermi acceleration, betatron acceleration, parallel electric field acceleration along magnetic fields and direct acceleration by the reconnection electric field. However, none of them have been experimentally confirmed, as the direct observation of non-thermal particle acceleration in laboratory experiments has been difficult due to short Debye lengths for in situ measurements and short mean free paths for ex situ measurements. Here we report the direct measurement of accelerated non-thermal electrons from magnetically driven reconnection at lowβin experiments using a laser-powered capacitor coil platform. We use kilojoule lasers to drive parallel currents to reconnect megagauss-level magnetic fields in a quasi-axisymmetric geometry. The angular dependence of the measured electron energy spectrum and the resulting accelerated energies, supported by particle-in-cell simulations, indicate that the mechanism of direct electric field acceleration by the out-of-plane reconnection electric field is at work. Scaled energies using this mechanism show direct relevance to astrophysical observations.