Magnetospheric Multiscale Satellite Observations of Parallel Electron Acceleration in Magnetic Field Reconnection by Fermi Reflection from Time Domain Structures

The same time domain structures (TDS) have been observed on two Magnetospheric Multiscale Satellites near Earth's dayside magnetopause. These TDS, traveling away from the X line along the magnetic field at 4000 km/s, accelerated field-aligned similar to 5 eV electrons to similar to 200 eV by a single Fermi reflection of the electrons by these overtaking barriers. Additionally, the TDS contained both positive and negative potentials, so they were a mixture of electron holes and double layers. They evolve in similar to 10 km of space or 7 ms of time and their spatial scale size is 10-20 km, which is much larger than the electron gyroradius (< 1 km) or the electron inertial length (4 km at the observation point, less nearer the X line).