Reversal ion source: A new source of negative ion beams

Abstract

We demonstrate a new type of ion source for producing either pulsed or continuous negative ion beams. The source, dubbed the ‘‘reversal ion source,’’ utilizes an electrostatic ‘‘mirror’’ which reverses trajectories in an electron beam, producing electrons at their turning point having a distribution of velocities centered at zero velocity. A gas which attaches zero-velocity electrons is introduced at this turning point. Negative ions are produced by the attachment or dissociative attachment process. The cross section for this process is extremely large, varying as (electron energy)−1/2, or just the s-wave threshold law. The operation of the source is demonstrated for continuous and pulsed production of Cl− beams by dissociative attachment to CFCl3. Estimates of the current density of this source are given, and applications to the production of ions through higher energy resonances are discussed.