Acknowledgments The authors would like to thank Professor B. D. Blackwell and Dr. Clive Michael at Plasma Research Laboratory of Australian National University, B. J. Ding at the Institute of Plasma Physics, Zh. H. Wang at the Southwestern Institute of Physics (SWIP) for helpful suggestions and comments, and Plasma Research Laboratory of Australian National University for providing the UFEM code. This work was supported by the National Natural Science Foundation of China (Grant Nos. 11205086 and 11675073), the Construct Program of Fusion and Plasma Physics Innovation Team in Hunan Province (NHXTD03), the Hengyang Key Laboratory Project (Grant No. 2018KJ108), and the Ph.D. Start-Up Fund of University of South China (2015XQD43).
