Demonstration of Beam Optics Optimization Using Plasma Grid Bias in a Negative Ion Source

Plasma grid bias has been utilized for reducing an electron density in the vicinity of a plasma grid in negative ion sources for fusion, resulting in achievement of low co-extracted electron current. In this study, the effectiveness and feasibility of the plasma grid bias on beam optics optimization are demonstrated. It is shown that the beam optics strongly depends on the bias voltage and is successfully optimized at different bias voltages depending on the discharge power. Responses of the beam properties such as the perveance and the current ratio to the plasma grid bias are also shown for both hydrogen and deuterium beams.