Artificial ion beam instabilities: 1. Linear theory

Abstract

Plasma instabilities that result when a heavy ion beam is injected into the F region ionosphere are studied using linear Vlasov theory. The background plasma model used consists of a relatively cool, collisionless O+‐dominated plasma with small concentrations of H+ and He+. Due to its large gyroradius (k⊥ρb ≫ 1), the beam is assumed to be unmagnetized and homogeneous. The beam density is taken to be on the order of or less than the background density. Instabilities in the frequency range from somewhat above the background lower hybrid frequency down to the O+ gyro‐frequency are studied. The instabilities are studied for various beam drift velocities, thermal velocities, and density regimes relevant to past sounding rocket experiments. It is shown that lower hybrid and ion‐ion hybrid instabilities dominate for drift velocities significantly larger than the H+ thermal velocity. For drifts on the order of the various background ion thermal velocities, instabilities of the various background ion Bernstein modes dominate. The importance of the transition from the kinetic to the fluid version of the instabilities is also discussed. The results of the linear theory are compared to experimental observations of plasma waves from past experiments. The agreement is very favorable.