Magnetic reconnection experiment using laser-produced plasma and external magnetic field
Toseo Moritaka1*, Taichi Morita2, Yasuhiro Kuramitsu1, Yuan Dawei3, Zhe Zhang3, Youichi Sakawa4, Yukiko Hara4, Hiroshi Shimogawara4, Yutong Li3
1Department of Physics, National Central University, Taoyuan, Taiwan
2Graduate School of Engineering Science, Kyushu University, Fukuoka, Japan
3Institute of Physics, Chinese Academy of Sciences, Beijing, China
4Institute of Laser Engineering, Osaka University, Osaka, Japan
* presenting author:Toseo Moritaka,
Magnetic reconnection has been considered to play an important role in high-energy space and astrophysical plasma phenomena. The reconnection process is characterized by two factors. One is macroscopic transition of magnetic field topology. The other is microscopic dissipation of anti-parallel magnetic fields, which triggers the magnetic reconnection. The full picture of magnetic reconnection has not been understood yet by satellite observations and numerical simulations because of this multi-hierarchical feature. Basic experiments on magnetic reconnection using dense laser-produced plasmas have recently started in intense laser facilities. Scale parameters of magnetic reconnection are minimized in high density plasmas and strong magnetic fields. We can thus apply multiplex measurements including optical imaging, electron spectrography and so on. Permanent or electro- magnets around the solid targets can generate stationary and controlled anti-parallel magnetic fields while laser-induced magnetic fields are extremely strong but nonstationary.

We carried out magnetic reconnection experiments using pairs of solid targets and permanent magnets with GXII laser facility at Osaka University and SGII laser facility at Shanghai Institute of Optics and Fine Mechanics. Two plasma flows from the solid targets collide with each other in various magnetic field configurations (parallel / anti-parallel magnetic fields and no magnetic field). Magnetic field strength(~ O(0.1)[T]) is enough strong to magnetize electrons but not enough strong to magnetize ions. Nevertheless, we observed clear dependencies of electron energy spectrum on the background magnetic field. A peak of 100 keV electrons arises in the energy spectrum only for the anti-parallel magnetic field case. In addition, slight differences were detected in the plasma density structures obtained for different magnetic field conditions. We will present the details of the experimental results and possible explanations based on hybrid particle-in-cell simulations. We will also discuss about further development of the experiment with more intense magnetic fields.

Keywords: Magnetic reconnection , Space and astrophysical plasmas, Laser plasma experiment