Electron acceleration in a coil target-driven low-<i>β</i> magnetic reconnection simulation

Yu Jiacheng; Zhong Jiayong; Ping Yongli; An Weiming

doi:10.1063/5.0149259

Volume 8 Issue 6

Nov. 2023

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Yu Jiacheng, Zhong Jiayong, Ping Yongli, An Weiming. Electron acceleration in a coil target-driven low-β magnetic reconnection simulation[J]. Matter and Radiation at Extremes, 2023, 8(6): 064003. doi: 10.1063/5.0149259

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Yu Jiacheng, Zhong Jiayong, Ping Yongli, An Weiming. Electron acceleration in a coil target-driven low-β magnetic reconnection simulation[J]. Matter and Radiation at Extremes, 2023, 8(6): 064003. doi: 10.1063/5.0149259

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Electron acceleration in a coil target-driven low-β magnetic reconnection simulation

doi: 10.1063/5.0149259

Department of Astronomy and Institute for Frontiers in Astronomy and Astrophysics, Beijing Normal University, Beijing 100875, China

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Corresponding author: a)Author to whom correspondence should be addressed: jyzhong@bnu.edu.cn
Received Date: 2023-03-05
Accepted Date: 2023-08-04

Available Online: 2023-11-01

Publish Date: 2023-11-01

Abstract

Abstract

Magnetic reconnection driven by a capacitor coil target is an innovative way to investigate low-β magnetic reconnection in the laboratory, where β is the ratio of particle thermal pressure to magnetic pressure. Low-β magnetic reconnection frequently occurs in the Earth’s magnetosphere, where the plasma is characterized by β ≲ 0.01. In this paper, we analyze electron acceleration during magnetic reconnection and its effects on the electron energy spectrum via particle-in-cell simulations informed by parameters obtained from experiments. We note that magnetic reconnection starts when the current sheet is down to about three electron inertial lengths. From a quantitative comparison of the different mechanisms underlying the electron acceleration in low-β reconnection driven by coil targets, we find that the electron acceleration is dominated by the betatron mechanism, whereas the parallel electric field plays a cooling role and Fermi acceleration is negligible. The accelerated electrons produce a hardened power-law spectrum with a high-energy bump. We find that injecting electrons into the current sheet is likely to be essential for further acceleration. In addition, we perform simulations for both a double-coil co-directional magnetic field and a single-coil one to eliminate the possibility of direct acceleration of electrons beyond thermal energies by the coil current. The squeeze between the two coil currents can only accelerate electrons inefficiently before reconnection. The simulation results provide insights to guide future experimental improvements in low-β magnetic reconnection driven by capacitor coil targets.

Conflict of Interest
The authors have no conflicts to disclose.
Jiacheng Yu: Data curation (equal); Formal analysis (equal); Investigation (equal); Methodology (equal); Software (equal); Writing – original draft (equal). Jiayong Zhong: Conceptualization (equal); Funding acquisition (equal); Project administration (equal); Supervision (equal); Validation (equal); Writing – review & editing (equal). Yongli Ping: Formal analysis (equal); Funding acquisition (equal); Methodology (equal); Software (equal); Supervision (equal); Validation (equal); Writing – review & editing (equal). Weiming An: Funding acquisition (equal); Software (equal); Supervision (equal); Writing – review & editing (equal).
Author Contributions
The data that support the findings of this study are available from the corresponding author upon reasonable request.
We performed two simulations with reference to the parameters of Yuan et al.²⁶ and Chien et al.,²⁵ respectively, and the results as shown in Figs. 9 and 10. The relevant parameters for both simulations are given in Tables II and III. The electron energy spectrum in all three simulations has a bump, but the spectral indices are slightly different. The differences in the non-thermal spectral index of the electrons in these simulations are within the error bars. Coil radius, coil separation, and current rise time may all contribute to the small variations in the spectral index. The exact reasons need to be investigated by further simulations. Figures 9(c)–9(e) and 10(c)–10(e) show a similar spatial distribution as in Fig. 6, and the acceleration curves for all three simulations indicate that the contribution of the betatron acceleration is the largest. These results support the previous conclusion that the betatron mechanism is the dominant mechanism for electron acceleration during magnetic reconnection.

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References(38)

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