Measurement of jet evolution and electron energy spectrum during the process of laser-driven magnetic reconnection
Authors: Zhang Kai  , Zhong Jia-Yong  , Pei Xiao-Xing  , Li Yu-Tong  , Sakawa Youichi  , Wei Hui-Gang  , Yuan Da-Wei  , Li Fang  , Han Bo  , Wang Chen  , He Hao  , Yin Chuan-Lei  , Liao Guo-Qian  , Fang Yuan  , Yang Su  , Yuan Xiao-Hui  , Liang Gui-Yun  , Wang Fei-Lu  , Zhu Jian-Qiang  , Ding Yong-Kun  , Zhang Jie  , Zhao Gang  ,   Key Laboratory of Optical Astronomy, National Astronomical Observatories, Chinese Academy of Sciences, Beijing 100012, China;,   University of Chinese Academy of Sciences, Beijing 100049, China;,   Department of Astronomy, Beijing Normal University, Beijing 100875, China;,   Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China;,   Institute of Laser Engineering, Osaka University, Osaka 565-0871, Japan;,   Shanghai Institute of Laser Plasma, China Academy of Engineering Physics, Shanghai 201800, China;,   Department of Physics, Shanghai Jiao Tong University, Shanghai 200240, China;,   National Laboratory on High Power Lasers and Physics, Shanghai 201800, China;,   Research Center for Laser Fusion, China Academy of Engineering Physics, Mianyang 621900, China
Published: December 2020

Magnetic reconnection (MR) is a universal physical process in plasma, in which the stored magnetic energy is converted into high-velocity flows and energetic particles. It is believed that MR plays an important role in many plasma phenomena such as solar fare, gamma-ray burst, fusion plasma instabilities, etc.. The process of MR has been studied in detail by dedicated magnetic-driven experiments. Here, we report the measurements of magnetic reconnection driven by Shenguang II lasers and Gekko XVII lasers. A collimated plasma jet is observed along the direction perpendicular to the reconnection plane with the optical probing. The present jet is very different from traditional magnetic reconnection outflows as known in the two-dimensional reconnection plane. In our experiment, by changing the delay of optical probing beam, we measure the temporal evolution of jet from 0.5 ns to 2.5 ns and its velocity around 400 km/s is deduced. Highcollimated jet is also confirmed by its strong X-ray radiation recorded by an X-ray pinhole camera. With the help of optical interferograms we calculate the jet configuration and its density distribution by using Abel inverting technique. A magnetic spectrometer with an energy range from hundred eV up to one MeV is installed in front of the jet, in the direction perpendicular to the reconnection plane, to measure the accelerated electrons. Two cases are considered for checking the acceleration of electrons. The results show that more accelerated electrons can be found in the reconnection case than in the case without reconnection. We propose that the formation and collimation of the plasma jet, and the electron energy spectrum may be possible directly influenced by the reconnection electric field, which is very important for understanding the energy conversion in the process of MR and establishment of the theoretical model. Finally the electron energy spectra of three different materials Al, Ta and Au are also shown in our work. The results indicate that the higher atomic number material can obtain a better signal-noise ratio, which provides some helpful references for our future work.