On November 10, Prof. Zhigang Yuan and his team, from School of Electronic Information in Wuhan University, have published their new findings on accelerated electron hole in space plasma in Nature Communications, titled as “Observational evidence of accelerating electron holes and their effects on passing ions”. PhD candidate Yue Dong is the first author, Prof. Yuan is the corresponding author, and the first affiliations is School of Electronic Information in Wuhan University. Electron holes with a Debye scale, also known as electron phase-space holes, are local structures in phase space where the electron density is lower than that of the surrounding plasma. They are often characterized as solitary-wave structures in electric field detection. Being a widely existing nonlinear isolated structure in space plasma, it has become a hot topic in the study of plasma nonlinear evolution due to its significant role in the nonlinear evolution of plasma particles. Although the research on electron holes spans over 60 years, previous studies have primarily presumed that electron holes move at a constant speed, leading to the conclusion that they cannot generate net acceleration in plasma flowing through such structures. In recent years, theoretical research suggests that accelerated electron holes can generate net acceleration on plasma passing through the structure, but this theory lacks observational confirmation. Thus, it remains a mystery whether accelerated electron holes exist and whether electrostatic solitary waves with symmetric electric fields in the direction of the field can generate net acceleration on the plasma passing through this structure. In response to the key issues mentioned, Prof. Yuan’s team employed the latest Magnetospheric Multiscale (MMS) satellite with high spatiotemporal resolution observations to analyze electric field data from multiple satellites using coherent analysis. This led to the discovery of electron holes in Earth's magnetospheric plasma sheet. The drift velocities of the electron holes are similar to the thermal speed of background ions, suggesting they are slow electron hole. The acceleration rate of electron holes is determined by the gradient of the background ion velocity distribution function at the drifting velocity of electron holes. By comparing theoretical calculations with observations, it was found that electron holes' acceleration results in a net acceleration of ions passing through the structure. This research confirms the existence of accelerated electron holes and uncovers their microscopic interaction with background ions, paving a new way for energy exchange between plasma regions along and against the magnetic field direction in collisionless plasmas.
The interaction of slow electron holes with ion double-humped velocity distributionThe co-authors of this study also include Prof. Shiyong Huang, Dr. Zuxiang Xue, and Dr. Xiongdong Yu from our institute. Dr. C.J. Pollock from Denali Scientific in USA, Prof. R.B. Torbert from the University of New Hampshire, and Prof. J.L. Burch from Southwest Research Institute in USA provided important assistance in interpreting observational events and ensuring satellite data reliability. This work is supported by the National Natural Science Foundation of China (41925018, 41874194).
