A boundary‐value problem treatment of an electric dipole in a warm isotropic plasma using the multiple water bag model

Abstract

A boundary‐value problem for a dipole immersed in a warm isotropic plasma has been solved using the multiple water bag (MWB) and fluid models of the plasma. The MWB model contains information on the electron distribution function, and hence gives results in agreement with the kinetic theory of the warm plasma. Comparing results from the MWB model with those from the fluid model, we find that the latter are correct only when the antenna frequency ω is sufficiently above the plasma frequency ωp. The current distribution and the driving‐point impedance are calculated for dipoles of several lengths. We find that the current distribution is triangular only when ω is well above ωp or when ω < ωl where ωl, is the frequency at which a resonance occurs in the driving point admittance; ωl is less than ωp and decreases with the increasing length of the dipole. The current distribution for frequencies close to ωp is oscillatory, with a complex wavenumber which is close to the wavenumber of the third‐order Landau mode. Only for very short dipoles with lengths less than 10 Debye lengths or so can the current distribution be approximated by a triangular one for all frequencies. The calculated frequency variation of the dipole resistance with frequency based on the MWB model is similar to those measured experimentally; for frequencies just below ωp the theory in this paper predicts a much larger resistance for the dipole than previous theories.