Hydromagnetic waves in a partially ionized hydrogen plasma

This paper gives further experimental verification of the theory of fast hydromagnetic waves. By a suitable choice of plasma conditions the compressional wave is propagated in a partially ionized cylindrical hydrogen plasma at frequencies below the ion cyclotron frequency. The propagation constants of the wave are measured experimentally by observing the phase velocity and attenuation over a fixed distance. Other plasma parameters, with the exception of the neutral density are measured independently. To obtain good experimental agreement with the theoretical curves computed from the measured data, it is necessary to postulate a considerable neutral particle density in the plasma. This gives rise to loading of the wave, observable as a reduction in the Alfvén speed, and also to wave damping not explicable by resistive effects alone. The enhanced loading produced by neutral particles is unaffected by variations in magnetic field and the fitted value of neutral density derived from wave cut-off data is in agreement with that calculated from attenuation measurements.