EXPANSION MODEL OF THE NEUTRAL COMPONENT IN VACUUM ARC SPOT PLASMAS

Plasma generated by cathode spots in vacuum arcs expands towards the a node and the walls. In spite of a high degree of ionization (mostly), this plasma contains also a small but noticeable constituent of neutra l atoms. Starting from the known analytical solution of a hydrodynamic model describing the plasma ions and electrons, the corresponding mot ion of neutrals is treated in a similar way. The results show: 1) The neutrals take part in the general plasma expansion; however, their fin al kinetic energy is lower (by about 50%) than the final energy of the ions. 2) The temperature of the neutrals also is lower than the ion t emperature and decreases during expansion. 3) The acceleration of neut rals is caused partly by the pressure gradient, partly by interaction with the ions (friction); the forces diminish rapidly with increasing distance. Finally, the limitations of this approximate solution are di scussed.