Electron heating associated with magnetic reconnection and magnetic holes in foreshock waves: PIC analysis

Kinetic structures like magnetic reconnection and magnetic holes develop in the shock transition region. They are potentially important sites for contributing energy dissipation at the shock, but their roles in plasma heating are still unclear. One pathway of generating such kinetic structures is that the ion-ion instability in the foreshock region excites ion-scale waves, which grow into large amplitudes, compress, and form thin current layers or generate secondary instabilities that allow reconnection to occur. We perform a 2D particle-in-cell simulation starting from the ion-ion instability, which indeed develops reconnection and magnetic hole structures. The probability distribution of the electron temperature indicates that electron heating is enhanced around the reconnection X-line. Heating starts from the magnetic field compression process before forming thin current sheets, which may lead to complicated temperature profiles in individual current sheets, and the heating efficiency also has temporal variations. The simulation also shows development of magnetic hole structures, where magnetic fields compress to form magnetic bottle structures that gradually evolve into electron-scale magnetic holes associated with electron temperature enhancements. The correlation analysis between the magnetic field strength and electron temperature indicates that the electron heating is adiabatic at large scales with positive correlations, while non-adiabatic heating occurs at sub-ion scales where the correlation coefficients are negative. The results demonstrate the importance of sub-ion scale reconnection or magnetic holes in electron heating at shocks.