Experimental Evidence of Plasmoids in High-β Magnetic Reconnection

Magnetic reconnection is a ubiquitous and fundamental process in plasmas by which magnetic fields change their topology and release magnetic energy. Despite decades of research, the physics governing the reconnection process in many parameter regimes remains controversial. Contemporary reconnection theories predict that long, narrow current sheets are susceptible to the tearing instability and split into isolated magnetic islands (or plasmoids), resulting in an enhanced reconnection rate. While several experimental observations of plasmoids in the regime of low-to-intermediate-beta (where beta is the ratio of plasma thermal pressure to magnetic pressure) have been made, there is a relative lack of experimental evidence for plasmoids in the high-beta reconnection environments which are typical in many space and astrophysical contexts. Here, we report strong experimental evidence for plasmoid formation in laser-driven high-beta reconnection experiments.

磁重联（magnetic reconnection）是等离子体（plasmas）中普遍存在且兼具基础性的物理过程，该过程中磁场会改变自身拓扑结构并释放磁能。尽管已有数十年的研究积累，但诸多参数域内支配重联过程的物理机制仍存在争议。当代重联理论预言，狭长的电流片易受撕裂不稳定性（tearing instability）影响，会分裂为孤立的磁岛（magnetic islands）或等离子体团（plasmoids），从而使重联速率得到增强。尽管在低至中等β区域（β为等离子体热压与磁压的比值）已完成若干等离子体团的实验观测，但在诸多空间与天体物理环境中常见的高β重联环境下，相关实验证据仍相对匮乏。本文报道了激光驱动高β重联实验中等离子体团形成的有力实验证据。