Alfvén wave propagation in a partially ionized plasma

Results from a laboratory study of the dispersion relation of Alfvén waves propagating through a partially ionized plasma are presented. The plasma is generated using a helicon source, creating a high density, current-free discharge, where the source can be adjusted to one of several modes with varying neutral fraction. Depending on the neutral fraction, the measured dispersion curve of shear Alfvén waves can change significantly. Measurement results are compared with theoretical predictions of the effect of neutral particles on Alfvén wave propagation. In fitting the theory, the neutral fraction is independently estimated using two simple particle transport models, one collisionless, the other collisional. The two models predict comparable neutral fractions, and agree well with the neutral fraction required for the Alfvén dispersion theory.