DENSITY GRADIENT EFFECTS ON ALFVEN WAVE PROPAGATION.
Abstract
The propagation of nonaxisymmetric, low-frequency Alfven waves in a nonuniform plasma has been investigated theoretically and experimentally. It was found that the density gradient introduces a frequency-dependent coupling between the torsional and compressional waves of the uniform plasma. As a result, an axial component of the magnetic field perturbation, which is normally associated only with the compressional wave, is now carried by th torsional wave as well, and was in fact detected at frequencies well below the lowest cutoff frequency of the compressional wave. In the theoretical analysis of the fully ionized, infinitely conducting plasma, the compressional wave is found to propagate as a sum of discrete modes, as in th case of a uniform plasma, except that the waveguide cutoff frequencies are those corresponding to an averaged mass density. However, the torsional wave is represented by a continuous spectrum of singular modes with wave numbers associated with th continuous distribution of values of the Alfven speeds which exist because of the density gradient. The total signal is then given by a superposition of these modes times a weighting factor determined by the source conditions.
Document Details
- Document Type
- Technical Report
- Publication Date
- May 01, 1966
- Accession Number
- AD0484681
Entities
People
- D. A. Mcpherson
- D. C. Pridmore-brown
Organizations
- The Aerospace Corporation