Radiation From an Oscillating Magnetic Dipole in a Streaming Plasma

Abstract

The electromagnetic field of an oscillating magnetic dipole is calculated, assuming that the dipole is immersed in a cold, streaming plasma. The amplitude of the magnetic dipole moment is assumed to be sufficiently weak that the linearized cold‐plasma equations may be used to describe the response of the plasma.The resulting field of the dipole is rather different from the field that would result if the plasma were not streaming. In particular, a longitudinal electrostatic field appears as a consequence of the plasma's motion. The far field of the dipole is such that the Poynting vector is not purely radial, but is tilted against the direction of the zeroth‐order plasma flow.An outward flow of mechanical energy is associated with the electrostatic field. However the mechanical energy flow is negligible for streaming velocities small compared with the velocity of light. The force necessary to hold the dipole in place is also calculated. This force vanishes when the dipole axis is parallel to the streaming direction, as does the longitudinal electric field.