The effect of negative ions on collision‐dominated Thomson scattering

Abstract

An expression for the collision‐dominated Thomson scatter power spectrum is derived from the fluid or continuum equations. This expression includes the possibility of multiple ion species of arbitrary charge. The total power and power spectral shape are investigated for scattering from a plasma composed of negative ions, positive ions, and electrons. The results indicate that total scattered power is modified by negative ion presence and that a limited amount of information about the negative ion content of the ionospheric D region may be found from Thomson scatter experiments. In particular, negative ions are found to increase the width of the power spectrum as would increased ion temperature or decreased ion neutral collision frequency. Spectra over a wide range of parameter values display the property of ‘scaling’: however, this effect may be sorted out such that negative ion presence is deduced from anomalously small ion‐neutral collision frequencies.