Electromagnetic waves and instabilities from cometary ion velocity shell distributions

Abstract

This paper considers the linear theory of electromagnetic waves and instabilities in the solar wind in the presence of cometary ions with complete velocity shell distribution functions. A collisionless, homogeneous plasma, propagation parallel or antiparallel to a uniform magnetic field and frequencies below the proton cyclotron frequency are considered. If there is no relative drift speed between the cometary ions and the solar wind protons, both right‐ and left‐hand polarized modes are stable, with ion cyclotron damping at wavenumbers of the order of the inverse cometary ion gyroradius. If there is a relative drift between the cometary ions and the solar wind protons greater than the Alfvén speed, both the ion/ion right‐hand and left‐hand resonant instabilities grow with maximum growth rates which increase as the shell distributions become narrower in velocity space.