Experiments on Alfvén-Wave Propagation

Abstract

Torsional hydromagnetic waves are generated in a cylindrical hydrogen plasma. The device that generates the plasma is described. Spectroscopic observation of Stark‐broadened Balmer lines gives the ion density as a function of time and indicates that the plasma is highly ionized. Reflections of the hydromagnetic waves are observed from high‐ and low‐impedance boundaries, and from a plasma‐neutral gas interface. The phases of the reflected waves are found to agree with theory. The driving current that generates the waves is analyzed in terms of Newcomb's principal modes. The measured radial distribution of the wave magnetic field is in fair agreement with this analysis, and the observed wave magnetic field amplitude agrees to within 15% with that predicted on the basis of the voltage applied at the driving electrode, decreased by the measured damping factor. Two different types of measurement suggest that the decaying plasma is electrically isolated from the (conducting) walls.