Recently, Ph.D. candidate XU Shanshan, Professor LIN Jun, and Associate Professor MEI Zhixing of Yunnan Observatories have conducted an in-depth study on the magnetic reconnection process driven by rapidly expanding plasma through magnetohydrodynamic (MHD) numerical simulations. Their work reveals the fine structure and physical mechanisms involved. The findings were recently published in Science China Physics, Mechanics & Astronomy.

The study employed 2D and 2.5D MHD numerical simulations to examine three modes of magnetic reconnection: flux pile-up, Sonnerup, and hybrid. These modes result from variances in gas pressure and magnetic field strength in the reconnection inflow region. The simulations demonstrate that the Spitzer diffusion region forms not as a simple X-point, but as a slim and elongated current sheet generating two pairs of the slow-mode shock (SS) on either end. These shocks contribute to forming four boundaries that separate the inflow from the outflow.

Further analysis reveals that, far from the Spitzer diffusion region, two sets of rotational discontinuities (RD) lie inward of the slow shocks (SS), forming an SS/RD compound structure. The RDs cause a reversal of the magnetic field direction in the reconnection outflow region, creating a distinctive W-shaped magnetic field configuration. The scenario that the rotation of the magnetic field is not caused by an intermediate wave, and the SS is located outside the RD.

This research provides a refined and novel perspective on the  processes of rapidly driven magnetic reconnection through numerical experiments. It deepens our understanding of this fundamental physical process and holds significant theoretical implications for explaining explosive energy-release phenomena in laboratory, solar, and space plasmas.

This work was supported by the National Key R&D Program of China, the National Natural Science Foundation of China (Key Program), the Yunnan Provincial High-level Talent Program (Yunling Scholars), and the Yunnan Solar Physics Research Studio. Numerical computations were performed at the Computational Solar Physics Laboratory of the Yunnan Observatories.

Contact:
LIN Jun
Yunnan Observatories, CAS
Email: jlin@ynao.ac.cn