Jeremy Mark Hanna

Alfvén wave propagation in a partially ionized plasma

Results from a laboratory study of the dispersion relation of Alfven 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 Alfven waves can change significantly. Measurement results are compared with theoretical predictions of the effect of neutral particles on Alfven 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 Alfven dispersion theory.

Alfvén wave propagation in a helicon plasma

Alfven wave propagation in a helicon plasma is being studied in the Auburn Linear Experiment for Space Plasma Investigations. The helicon discharge provides the high-density plasma necessary to propagate Alfven waves. Shear Alfven waves are produced in this discharge by means of an inductive coil positioned to oscillate the magnetic field perpendicular to the background field lines. The waves are detected by means of a second inductive coil positioned down the plasma column. Initial investigations demonstrate the propagation of shear Alfven waves within the plasma through the localization of the oscillations along the magnetic-field lines and the expected phase velocity of the waves.