Electron acceleration in reconnecting and non-reconnecting current sheets in the Earth's quasi-parallel bow shock

In quasi-parallel shock waves, turbulence occurs in the shock transition region due to instabilities such as the ion-ion beam instability, which eventually bends magnetic field lines and current sheets are produced. There are two types of current sheets in the shock turbulence region: reconnecting current sheets and non-reconnecting current sheets. In the Earth’s bow shock, NASA’s Magnetospheric Multiscale (MMS) has been observing many current sheets, some of which show evidence of magnetic reconnection and energetic accelerated particles. 

 

We study electron acceleration in the Earth’s quasi-parallel bow shock by means of 2D particle-in-cell (PIC) simulation. We discuss differences in properties in reconnecting and non-reconnecting current sheets. Reconnecting current sheets and magnetic islands produced by reconnection show significant heating and energetic particles, and several acceleration mechanisms work in these regions: Fermi acceleration, Hall electric field acceleration, and island betatron acceleration. We also demonstrate that electrons are energized in non-reconnecting current sheets. In some regions in turbulence, an elongated, extending current sheet is formed, and electrons can be accelerated by the perpendicular electric field inside the non-reconnecting current sheet. We compare the efficiency between the acceleration mechanisms in reconnection regions and non-reconnecting current sheets.