The dynamics of electron-ion coupling in the shock transition region

In the shock transition region the process of electron-ion coupling under Buneman instability between inflow electrons and reflected ions is investigated. Buneman instability often evolves into a highly nonlinear state with strong wave-particle interaction like velocity phase hole (vortex) dynamics. Previous studies have shown that these electron holes contribute to the strong electron heating and acceleration. In this study, how electron holes affect the ions and interact with them is examined. Under the condition of Buneman instability dominant, the electron holes preserve their coherent large-amplitude structure for a sufficiently long period of time to modify the ion population electrostatically. Electron holes resonate with the ion population through the ion-acoustic branch, and then some of the inflow ions are rapidly decelerated and reflected by the electric field at the electron holes. As a result of gaining additional energy from the inflow ion population, the amplitude of the electric field of the hole becomes 40% larger than what was estimated in some previous studies, which did not take the coupling ions into account. Although the electron hole-ion coupling state is seen in such a small scale as electron inertia length (c/omega(pe)), this large electric field of the electron hole leads to a strong disturbance and heating of the plasma. This study may provide a first indication of what regulates strong electron heating in the shock transition region through the coupling process between the electrons and ions. (C) 2003 American Institute of Physics.