The use of magneto-acoustic oscillations as a plama diagnostic technique

A theoretical and experimental investigation of the forced radial magnetoacoustic oscillations of a magnetized plasma column is presented in this paper. Forced magneto-acoustic oscillations of a magnetized argon afterglow plasma are generated continuously by passing an RF current through a solenoid wrapped around the discharge tube. The radial variation of the amplitude of the magnetic field disturbance [bz(r)] associated with these oscillations is measured at various times during the decay of the afterglow plasma. A theoretical description of these oscillations is developed in which the collision frequencies between the various plasma constituents are treated as free parameters. The values of these free parameters at any given instant during the decay of the plasma are determined by fitting computed bz{r) radial profiles to the measured ones. The electron temperature Te, and the ion-neutral cross section for momentum transfer QD are deduced from these collision frequencies. The reliability of this plasma diagnostic technique is demonstrated by its ability to yield values for Te and QD which compare favourably with the results obtained by other workers.