EARLY TIME EVOLUTION OF NEGATIVE-ION CLOUDS AND ELECTRON-DENSITY DEPLETIONS PRODUCED DURING ELECTRON-ATTACHMENT CHEMICAL-RELEASE EXPERIMENTS

Two-dimensional electrostatic particle-in-cell simulations are used to study the early time evolution of electron depletions and negative io n clouds produced during electron attachment chemical releases in the ionosphere. The simulation model considers the evolution in the plane perpendicular to the magnetic field and a three-species plasma that co ntains electrons, positive ions, and also heavy negative ions that res ult as a by-product of the electron attachment reaction. The early tim e evolution (less than the negative ion cyclotron period) of the syste m shows that a negative charge surplus initially develops outside of t he depletion boundary as the heavy negative ions move across the bound ary. The electrons are initially restricted from moving into the deple tion due to the magnetic field. An inhomogenous electric field develop s across the boundary layer due to this charge separation. A highly sh eared electron flow velocity develops in the depletion boundary due to E X B and del N x B drifts that result from electron density gradient s and this inhomogenous electric field. Structure eventually develops in the depletion boundary layer due to low-frequency electrostatic wav es that have growth times shorter than the negative ion cyclotron peri od. It is proposed that these waves are most likely produced by the el ectron-ion hybrid instability that results from sufficiently large she ars in the electron flow velocity.