Plasma electrode structure suitable for H^- extraction from Bernas type ion source

The plasma electrode structure of a Bernas type ion source was modified to increase negative hydrogen (H⁻) ion current. On the previous geometry the plasma electrodes was installed inside the ion source while the new geometry has the plasma electrode outside discharge chamber. The H⁻ ion beam current increased by positively biasing the plasma electrode to improve the ratio of the negative ion current and the extraction current to 2.4 times the original ratio for the electrode installed inside. The H⁻ ion beam current increased 1.2 times enhancement by tantalum (Ta) filament was also attempted. The Ta filament produce 20 % more H⁻ ion current and reduced extraction current by 50 %. The overall improvement by plasma electrode structure and Ta filament made the H⁻ ion to extraction current ratio to double.