Long Timescale 3D Simulations of an Electron Beam Penetrating a Plasma

When an electron beam encounters an overdense plasma, the beam is quickly destabilized by the two stream instability and dispersed. However, it was shown previously by means of 2D simulations that over long time scales the beam ejects the background electrons from the region where the beam is propagating, leaving the background ions to neutralize the beam charge, thus stabilizing the beam propagation over timescales that are long compared to the electron-electron two stream instability growth time. In this report, long timescale simulations in 3D are presented. In the overdense regime, the background electrons are not completely blown away and the beam electrons encounter the remaining background electrons. On short timescales the beam is destabilized by the two stream instability and dispersed. However, the result of this dynamics is the that background electrons are dispersed and then over timescales that are long compared to the electron-electron two stream instability growth time the beam reforms and digs a hole in the background plasma through which it can stably propagate. This demonstrates that even with 3D instabilities included the beam can indeed propagate through the overdense plasma.