[P-EM16] 宇宙プラズマ理論・シミュレーション

[PEM16-P03] Shock Drift Acceleration and Betatron Acceleration of Electrons at Nonstationary Quasi-Perpendicular Shocks

*大塚 史子¹、松清 修一¹、岡 光夫² (1.九州大学大学院総合理工学研究院、2.カリフォルニア大学バークレー校)

Electrons are accelerated to very high, non-thermal energies at Earth's quasi-perpendicular bow shock. Shock drift acceleration (SDA) is one of the most plausible model to produce non-thermal electrons at quasi-perpendicular collisionless shocks. In the SDA, electrons gradient-B drifting along the shock gain energy from the motional electric field. Betatron acceleration is also candidate for the energy gain at a nonstationary shock, where an overshoot magnetic field is compressed during the shock self-reformation process.

In this study, we quantify the contributions of the SDA and betatron effects on an electron acceleration process in a quasi-perpendicular shock, by performing PIC simulations. The shock parameters are as follows. The Alfven Mach number is 7, upstream plasma beta is 0.3, the shock angles are 70 degrees. We investigate which electric field components contribute to the electron energy gain, by analyzing the trajectories of electrons trapped in a thin magnetic trough embedded in the overshoot magnetic field. The result shows that the betatron acceleration effectively occurs at least comparable with the SDA. We also discuss the effect of a cross-shock potential on the electron acceleration.