Ion Acoustic Wave Dispersion in a Highly Ionized Argon Plasma in a Magnetic Field

Ion acoustic waves have been magnetically excited and optically detected in a highly ionized argon plasma in the presence of a longitudinal magnetic field. The dispersion of the waves has been studied as a function of the exciting frequency between 187 kHz and 352 kHz and with the confining static magnetic field in the range 800-2200 G. A dispersion relation is derived which includes the combined effects of ion drift velocity, ion thermal motion, damping, axial magnetic field, and finite beam geometry as adjustable parameters. Dispersion curves are presented which compare the experimental data to the dispersion relation, the parameters being evaluated by a least-squares fit. The agreement is good.