Numerical analysis of the production profile of H atoms and subsequent H− ions in large negative ion sources

Abstract

The production and transport processes of H0 atoms are numerically simulated using a three-dimensional Monte Carlo transport code. The code is applied to the large JAEA 10ampere negative ion source under the Cs-seeded condition to obtain a spatial distribution of surface-produced H− ions. In this analysis, the amount of H0 atoms produced through dissociation processes of H2 molecules is calculated from the electron temperature and density obtained by Langmuir probe measurements. The high-energy tail of electrons, which greatly affects H0 atom production, is taken into account by fitting a single-probe characteristic as a two-temperature Maxwellian distribution. In the H0 atom transport process, the energy relaxation of the H0 atoms, which affects the surface H− ion production rate, is taken into account. The result indicates that the surface H− ion production is enhanced near the high-electron-temperature region where H0 atom production is localized.