Hydromagnetic Waves in a Nonuniform Current Carrying Plasma Column

Abstract

The axially symmetric modes of propagation of hydromagnetic disturbances in a current-carrying plasma column with a nonuniform mass-density distribution are investigated. The current density is assumed to be uniform. The column is surrounded by a vacuum and immersed in a uniform axial magnetic field. In the limit of small discharge current, two uncoupled modes of oscillation can take place. One involves a radial pulsation of the column with associated pressure, density, and temperature fluctuations, while the other is a torsional motion. The torsional mode is not accompanied by fluctuations in the thermodynamic properties. The properties of both the radial and torsional mode such as phase velocity, group velocity, cutoff frequency (radial mode only) and attenuation are discussed in detail. The density gradient in the plasma is found to appreciably alter the torsional mode producing distortions in the wave fronts and significantly increasing the attenuation.