The Propagation of Compressional Alfven Waves in Nonuniform Plasmas

A theoretical treatment is presented for the propagation of Alfven waves in a plasma. It includes the effects of resistivity, ion-neutral collisions, the ion cyclotron frequency and radial nonuniformities in ion density, neutral particle density and temperature. The theory is applied to plasmas with conducting and nonconducting walls and the results are compared with those of experiments conducted in the afterglow of a shock-produced plasma. Nonuniformity in the ion density is found to have a marked effect on the dispersion relation and wave field profiles, while non uniformities in the total particle density and temperature are less important. Excellent agreement is obtained between theory and experiment and this allows unambiguous and accurate determinations to be made of the average total particle density, which is found to be - 50 % of the initial filling density, and of the cross section for momentum transfer between protons and hydrogen atoms.