Effect of Coulomb collision between surface produced H- ions and H+ ions on H- extraction mechanism and beam optics in a Cs-seeded H- ion source by 3D particle in cell model

Recently, in Cs-seeded H- ion sources for fusion applications, the experiments have shown that the surface produced H- ions are mainly extracted from the bulk plasma region, that is, 1-2 cm inside from the beam aperture. The purpose of this paper is to clarify the extraction mechanism of the surface produced H- ions from the bulk plasma region in Cs-seeded H- ion sources for fusion applications by our 3-Dimensional Particle in Cell model for the vicinity of the beam aperture. In the present model, Coulomb collisions between surface produced H- ions and H+ ions (CC H- -H+) are taken into account by the Binary Collision Model. By our model, the trajectories of extracted surface produced H- ions and beam profiles have been investigated for the case with and without CC H- -H+. From the results of trajectories for extracted surface produced H- ions, it has been shown that the surface produced H- ions extracted from the bulk plasma region are drastically increased due to CC H- -H+. Thus, our results have shown that the surface produced H- ions are extracted from the bulk plasma region due to Coulomb collision with H+ ions. Moreover, our results of the beam profiles have shown that CC H- -H+ causes the increase in the beam convergence component. From these results, Coulomb collisions between surface produced H- ions and H+ ions are shown to be very important for the modeling of the extraction mechanism and for the beam optics in Cs-seeded H- ion sources for fusion applications. Published by AIP Publishing.