Alan W. DeSilva

EXPERIMENTS ON ALFVEN-WAVE PROPAGATION

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 Newcombs 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.

Hydromagnetic Wave Propagation near Ion Cyclotron Resonance

A torsional hydromagnetic wave is induced by application of an oscillatory radial electric field to one end of a cylindrical deuterium plasma located in a magnetic mirror field. The wave propagates in the axial direction to the center of the device, where a resonance occurs between the hydromagnetic wave frequency and the local ion cyclotron frequency. Wave magnetic‐field measurements indicate that transfer of power from the 1‐MW, 8.3‐Mc oscillator to the hydromagnetic wave is about 65% efficient, and that more than 90% of the wave energy is transferred out of the wave at the resonance region.

Devices for generating highly-ionized hydrogen plasma

A set of closely-related devices for generating a highly-ionized hydrogen plasma is described. In each device a hydrogen plasma is created in a cylindrical tube immersed in an axial magnetic field of from 4 to 20 kG. The plasma is formed by a switch-on ionizing wave, driven from an external capacitor bank. In a typical tube 14.6 cm dia. and 86.4 cm long, with a magnetic field of 15 kG, an ion density of > 5 × 1015 cm-3 is attained in hydrogen of initial atomic density 6.6 × 1015 cm-3. The temperature of this plasma is between 10,000 and 30,000°K, and the plasma decays in several hundred microseconds by a volume-recombination process.

Swirls Produced in a ``Crowbarred'' Rotating Plasma

Hydromagnetic swirls develop in a rotating, gaseous plasma subjected to an electromagnetic braking action. Observations of these swirls and the effect of a conducting grid upon them are discussed.

Method for Defining Position of Magnetic Field Lines

The method described was developed during experiments on Alfven wave propagation. It was necessary to be sure that the hydromagnetic waveguide-was accurately aligned with a uniform axial field. Tests indicate that the method would be valuable for use with various complex magneticfield geometries that have been proposed for controlled thermonuclear heating. (B.O.G.)