Particle simulation of plasma response to an applied electric field parallel to magnetic field lines



[1] We study response of thermal plasmas to an induction electric field via one-dimensional particle simulations. The induction electric field is assumed to be uniform in space and constant in time. Because of acceleration of electrons and ions in the opposite directions, there arise counter streaming electrons and ions that cause the Buneman instability. Depending on the ratio of the ion temperature Ti to the electron temperature Te, responses to the electric field are different. For a case with hot ions (TiTe) the Buneman instability leads to formation of large isolated electrostatic potentials which trap some electrons to move with ions. For a case with colder ions (TiTe) the Buneman instability is taken over by excitation of ion acoustic waves, which diffuse the low-energy part of the accelerated electrons to stabilize the instability. However, a substantial part of the electrons are grouped together at the high-energy part, forming a distinct bump in the electron distribution. In the present simulations we have found that the induction electric field can form an electron beam along the magnetic field line. Since the electron beam leaves the region of the induction electric field and moves into an unperturbed plasma, the accelerated electrons can cause a bump-on-tail instability. This can lead to formation of electrostatic solitary waves as frequently observed by the GEOTAIL spacecraft in the plasma sheet boundary layer (PSBL). The persistent observation of the electrostatic solitary waves indicates their association with the induction electric field that results from meandering motion of the current sheet in the magnetotail.