Electron holes, ion waves, and anomalous resistivity in space plasmas

Abstract

Phase-space electron holes are seen in simulations, laboratory plasmas, and many regions of the Earth's space environment. We present simulations of beam plasmas showing that the generation and decay of electron holes results in a reduction of electron current, implying a parallel resistivity. We show that resistivity occurs in simulations where a cold electron beam is coincident with a warmer background plasma and appears to be mediated by the generation of ion acoustic waves propagating obliquely to the magnetic field. Initially, electron holes scatter electrons in the beam direction, steepening the electron beam distribution, eventually launching ion acoustic waves that cause resistivity and strong ion heating perpendicular to B→. These effects occur in both strongly and weakly magnetized plasmas. Given that electron holes are observed in many space plasmas, these results have important implications for a number of magnetospheric and auroral ionospheric processes. For auroral plasmas, electron hole resistivity could support parallel electric fields on the order of several mV/m, accounting for parallel potential drops from tens to hundreds of eV. For the magnetopause, simulations show effective collision rates of 0.00015 ωpe, which could enhance dissipation and diffusion across the boundary. Copyright 2006 by the American Geophysical Union.