A theoretical method of predicting properties of free burning arcs and their cathodes is presented in a unified treatment. The method combines a one-dimensional model of the non-equilibrium plasma sheath adjacent to the cathode and a two-dimensional model for the arc column and the solid cathode. Two internal boundaries divide the arc-cathode domain into an arc region, a sheath region and a cathode region. The internal boundary conditions are adjusted during the iteration procedure to satisfy the energy conservation and current continuity equations. The effective resistance of the cathode sheath region is obtained from the sheath calculation assuming charge transport using an ambipolar diffusion approximation. No assumptions are made as to the distributions of, current density and temperature at the cathode surface. The model accounts for cathode surface effects and assumes that the cathode is a thermionic emitter. Material functions such as the thermal and electrical conductivities of the arc plasma and cathode are required as input parameters. Predictions are made, for any given arc current and cathode configuration, of the temperature and current density distributions in the arc and the cathode. Information is also provided about sheath properties. The results from a calculation for 200 A arc burning in argon with a thoriated tungsten cathode are in good agreement with the experimental measurements of the arc column and cathode surface temperatures and the arc voltage.

Predictions of the temperatures of the anode of free burning arcs are made using a theory that treats an arc and its electrodes as a unified system. The theory predicts the temperature distributions of the arc column, the cathode and the anode as a function of the arc operating conditions. Temperature profiles on the surface of copper anodes for arcs in argon are calculated for various arc operating conditions. Theoretical predictions of the threshold current for melting a water-cooled copper anode range from 1260 to 480 A for anode thicknesses ranging from 2 to 10 mm and are in good agreement with experimental results.

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Nonthermal beamlike electron tails have been observed in an argon magnetoplasma excited by rf without electron beam injecting. The plasma is highly ionized (-100%) with central density-1014 cmw3, and is based on the excitation of helicon waves. Nonthermal electron tails are observed at the beginning of the plasma pulse and last for about 1 msec. There is a maximum in the electron energy distribution at 30-80 eV and a minimum at 20-30 eV. The mechanism responsible for driving this beamlike tail is not yet known.

A theoretical dynamic model has been developed to predict the formation of molten droplets on a moving wire electrode in a gas metal welding arc. Calculations have been made of the droplet shape and size as a function of the welding current by accounting for the electromagnetic pinch effect, surface tension, gravitation and momentum transfer due to motion of the solid wire electrode. Our calculations start with an artificial cylindrical liquid column which, for low currents, develops into a droplet which is close to spherical. However, for currents above about 250 A, the magnetic pinch constricts the column such that a smaller elongated droplet is formed.