Thin free arcs in alkali-seeded noble gases

Thin arcs (e.g. those observed in noble gas magnetohydrodynamic generators) are analyzed. The spatial distributions of the important plasma quantities are calculated by solving the appropriate balance equations. Solutions are obtained for cesium-seeded argon as well as for pure argon. The solutions yield characteristic radial dimensions which are in agreement with known experimental values. The effects of variations of important arc parameters are discussed in the case of cesium-seeded argon. It appears that the effects of the parameter variations can be explained to a large extent by a simplified expression for the radial dimension of the arc. Deviation from local thermodynamic equilibrium is only significant in the outer region of the arc and has practically no influence on the arc properties