The modeling and analysis of a negative ion source is proceeding by using a 2D particle-in-cell simulation. The effect of the H- ion production on the plasma grid (PG) surface is investigated. It is shown that with the increase of H- ions per time step, the H- ion current density is enhanced, while the electron current density decreases with increasing the H- production rate on the PG surface. These results agree well with the experimental results observed in typical negative ion sources. Moreover, it is found that plasma quasi-neutrality is held mainly by both H+ and H- ions in the bulk plasma around the PG.
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