Structure of plasmas generated by the interaction between metallic ions and neutral gas particles in a low-pressure arc

A numerical solution for the metallic-plasma-neutral-gas structure generate d in a low-pressure arc is presented. The equations correspond to a spheric ally symmetric fluid-like steady model, valid for the outer region of the a rc, and describe the ion slowing down by elastic scattering with the neutra l particles. Technically, the obtention of the profiles of different magnit udes is complicated due to the existence of a critical point in the steady- state system of equations. The proposed approach to overcome this difficult y is to solve instead a pseudotransient system of equations which rapidly a nd efficiently relax to the stationary state. By employing this numerical m ethod of second-order accuracy in space, the plasma and neutral gas density , the electron and ion drift velocities, the electron and neutral temperatu res, and the electrostatic potential profiles are obtained from the border of the arc channel up to the discharge chamber wall. It is found that the v alue of the neutral gas filling pressure strongly influences the plasma den sity and plasma potential distributions. An important result is that metall ic ions emitted from the arc channel deliver their kinetic energy to the fi lling gas in a gradual manner, up to a pressure-dependent point beyond whic h they move to the walls sustained against collisions with the gas by a sel f-consistent electric field. Near the mentioned point, the metallic ion den sity presents a peculiar behavior, showing an increase that is more pronoun ced at high pressures; a pattern also evident in the electrostatic potentia l. (C) 2000 American Institute of Physics. [S0021-8979(00)07711-2].