Re-ionization of a partially ionized plasma by an Alfvén wave of moderate amplitude

This paper reports on the use of forced magneto-acoustic oscillations to investigate the effect of a torsional hydromagnetic (Alfvén) wave pulse of moderate amplitude on the properties of a partially ionized afterglow helium plasma. Observations of the magnetic flux associated with the oscillations, measured at a number of frequencies, are used to determine radial density proffles and to provide estimates of plasma temperature. The torsional wave is shown to cause significant re-ionization of the plasma with no corresponding increase in the plasma temperature. The torsional wave is shown to cause significant re-ionization of the plasma with no corresponding increase in the plasma temperature. However, the presence of a number of energetic particles is evidenced by the production of a significant number of doubly charged helium ions.