Analysis of the H- ion emissive surface in the extraction region of negative ion sources

To understand the plasma characteristics in the extraction region of negative H^- sources is very important for the optimization of H ^- extraction from the sources. The profile of plasma density and electrostatic potential in the extraction region with and without extraction grid voltage are analyzed with a 2D particle in cell modeling of the NIFS-RD H^- sources. The simulation results make clear the physical process forming a double ion plasma layer (which consists only of positive H⁺ and negative H^- ions) recently observed in the Cs-seeded experiments of the NIFS-RD source in the vicinity of the extraction hole and the plasma grid. The results also give a useful insight into the formation mechanism of the plasma meniscus and the H^- extraction process for such double ion plasma.