Production of Negative Helium Ions by Nearly-Resonant Charge Exchange in Potassium

The design criteria for a source of 5-10μA of He- ions suitable for tandem accelerator application have been investigated. The process used is a nearly-resonant charge exchange between He+ ions, from a duoplasmatron, and potassium vapor. In the He+ energy range of 5-25 keV, the He-/He+ yield has been measured as a function of He+ energy. Yields of ~2%/ have been observed. A He- beam emittance of 1.2 × 10-2 cm rad eV1/2 has been measured. The potassium flux into the system was found to be ~1016 particles/s.