Analysis of the H<SUP>-</SUP> ion emissive surface in the extraction region of negative ion sources

International audienceTo understand the plasma characteristics in the extraction region of negative H&#8722; sources is very important for the optimization of H&#8722; 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&#8722; sources. The simulation results make clear the physical process forming a double ion plasma layer (which consists only of positive H and negative H&#8722; ions) recently observed in the Cs-seeded experiments of the NIFS-R&D 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&#8722; extraction process for such double ion plasma