Monte Carlo simulation of negative ion production in the negative hydrogen ion source

Two Monte Carlo simulation codes: (a) neutral transport code and (b) negative ion (H^-) transport code, have been developed to understand transport phenomena in negative ion sources. In the neutral transport code, Boltzmann equations for hydrogen molecules (H₂) and atoms (H) are solved. Three dimensional (3D) spatial distributions of H₂, H, and H^- production are obtained for a tandem negative ion source. The volume production of H^- is limited to the area around the gas inlet in the first chamber and near the plasma grid in the second chamber. On the other hand, distribution of H^- surface production is shown to be almost uniform over all the plasma grid surface. In the negative ion code, H^- trajectories are calculated by numerically solving the 3D equation of motion for H^- ions. The effects of the magnetic filter on the extraction probability of surface produced H^- ions are mainly studied. The dependence of the extraction probability on the field strength is small.