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. [ABSTRACT FROM AUTHOR]