Measurements of emittance and species fractions of a positive hydrogen ion beam extracted from an RF-driven multicusp source

Measurements of the H⁺, H₂⁺, and H₃⁺ fractions and emittances of a hydrogen beam extracted from an RF-driven multi-cusp source were made using a bending magnet and an electrostatic emittance scanner. The H⁺ fraction increased with RF power. Fractions in excess of 90% were obtained. At a given RF power, the H⁺ fraction increased with decreasing source pressure and increasing filter rod separation. When the “collar” surrounding the extraction aperture (used for H ^- operation) was removed, the H⁺ current increased by a factor of ≈4, without changing the H⁺ fraction at a given RF power. With a large filter rod separation, H⁺ currents on the order of 100 mA were achieved at ≈20 kW of RF power. Using a modified extractor operating at 35 kV, H⁺ currents on the order of 60 mA were obtained with a 90% normalized rms emittance of 0.012 πcm-mrad