Strongly-perturbed non-equilibrium gas physics model for the paraxial diode transport cell

Intense short-pulse charged-particle beams - those with tens or hundreds of kA/cm/sup 2/ and beam risetimes less than 100 ns - can disturb the background gas so severely that not only are diatomic molecules ionized, but molecules may be dissociated and the product atoms themselves multiply ionized. Such beam-background systems are generally far from temperature and species equilibrium. The plasma conductivity /spl sigma/, which is determined by the degree of ionization and the species temperatures, strongly influences the beam behavior through the plasma return current. Thus, simultaneously and self-consistently solving for both /spl sigma/ and the beam propagation is essential for a correct description of the system behavior. A plasma physics model with advanced gas chemistry has been developed and incorporated into the simulation code LSP to help meet this objective.