Enhancement of H− production in a multicusp source by cold electron injection

The effect on H− production by injecting primary electrons with different energies into the three regions of a magnetically filtered multicusp source has been investigated. A substantial increase in H− yield occurs only when very low‐energy electrons (E≊1 eV) are added to the plasma in the filter or extraction chamber region. The measured increases were about 50% and 25%, respectively. This increase may indicate that the H− ions are formed by dissociative attachment of vibrationally excited H2. In that case, the low‐energy electron injection scheme could maintain a low average H− ion energy which in turn could improve the brightness of the extracted beam.