Quasineutral Beam Propagation in Space

Abstract

The propagation of dense energetic neutralized ion beams or plasmoids injected into a plasma across the ambient magnetic field under ionospheric conditions is considered. Using a simple physical model supported by two-dimensional hybrid simulations, it is shown that think dense beams can propagate ballistically over lengths many times their gyroradius. This occurs when the following conditions are satisfied: {Delta}/R{sub o} {much lt} 1, where {Delta} is the cross field beam width and R{sub o} the gyroradius of an ambient ion having a velocity equal to the beam velocity u{sub b}, and n{sub b}M{sub b}/n{sub o}M{sub o} {much gt} 1, where n{sub b}(M{sub b}), n{sub o}(M{sub o}) are the density (mass) of beam and ambient ions. The scaling of the ballistic propagation lengths and times with beam and ambient parameters is presented along with comments on the applicability of the model to space and astrophysics. 13 refs., 19 figs., 1 tab.