Two-Dimensional Particle Simulation of Electrostatic Solitary Waves with an Open Boundary Condition

Abstract

We study formation process of two‐dimensional electrostatic solitary waves observed by the GEOTAIL spacecraft. Previous simulation studies have confirmed that the electrostatic solitary waves correspond to BGK electron holes formed through nonlinear evolution of electron beam instabilities. In the present study, we performed two‐dimensional electrostatic particle simulations of an electron bump‐on‐tail instability with an open boundary condition. We inject a weak electron beam from the open boundary into the background plasma. In the two‐dimensional open system, spatial and temporal development of the electron bump‐on‐tail instability is different from that in the uniform periodic system. A lower hybrid mode is excited locally in the region close to the source of the electron beam through coupling with electron holes at the same parallel phase velocity, because the drift velocity of the electron holes is much faster than the parallel group velocities of the lower hybrid mode. As a result, spatial structures of electron holes vary depending on the distance from the source of the electron beam.