Numerical modeling of the LBL HIF ion source

Summary form only given. The requirements of HIF place severe restrictions on the operating parameters of the ion source. In addition to the usual requirements of high brightness, constant current, and constant energy/nucleon, it is necessary to switch the ion flow on abruptly with enough ion flux so that the full HIF pulse current requirement can be met without the flow becoming source limited. A technique that shows promise is a combination of an arc source with control grids. The grids are biased with a potential to confine electrons and thus switch off any ion flow until the grid voltage is overpowered by the abrupt application of the extraction voltage. The plasma feed from the arc sources must satisfy various criteria so that the plasma electrons neutralize the flow up to this switch grid, but no further, so that space charge limited flow can be maintained between the switch and extraction grid. The plasma-grid interaction has been modeled with the particle-in-cell code GYMNOS in the relevant parameter regime to verify the understanding of the switch-off requirements followed by the switch-on stage. It was found that the arc source must provide plasma with density and flow rates within a small range of parameters; otherwise, the grid cannot properly confine electrons-the essential elements for constant current during the pulse