Plasma electrode shape suitable for plasma electrode performance study.

A compact ECR ion source was used to investigate the effect that the shape of the plasma electrode (PE) has on the surface production of negative hydrogen (H⁻) ions. A C12A7 electride PE produced ten times more H-ion current compared with a molybdenum (Mo) PE of the identical design. Four times more H- ion current was obtained when the ion source plasma faces the 45-degree tapered hole opened on the surface of the electride PE as compared to the current obtained from a plasma facing the flat side of the PE. This enhancement in H- ion current may indicate larger surface production of H⁻ ions by the enlarged surface area. A Mo PE also showed a similar effect but with less pronounced H- ion current enhancement. A beam trajectory study showed that the beam divergence was larger when the source plasma faced against the tapered side of the PE. [ABSTRACT FROM AUTHOR]