Modeling of a negative ion source II. Plasma-gas coupling in the extraction region

The production, destruction, and transport of H- in the extraction region of a negative ion source are investigated with a 1D(z)-3V particle-in-cell electrostatic code. The motion of charged particles (e, H+, H2 +, and H-) in their self-consistent electric field is coupled with the neutral particles [H(n=1) and H2(X1sigmag+ , v=0, . . . ,14)] dynamics and vibrational kinetics of H2. Neutral influxes into the domain are determined by the simulation of the expansion region. Surface and volumetric processes involving plasma and neutrals have been included by using different Monte Carlo collision methods. Calculations show the influence of the plasma grid bias and of the magnetic filter on the plasma parameter profiles. In particular, a transition from classical to complete reverse sheath is observed using a positively biased plasma grid. The influence of the magnetic filter is small. The importance of the hot-atom mechanism on the surface negative ion production is shown.