Dependence of ion acceleration on limiting current in relativistic electron beams

A 2-MeV 15-kA 45-nsec electron beam was used to obtain high-energy deuterons when injected into a chamber filled with neutral deuterium at low pressure. It was found that ion acceleration did not occur until the electron current exceeded the space-charge limiting current, the threshold established by the acceleration model of Olson. The limiting current was varied through its dependence on the ratio of guide tube radius to injected electron beam radius. The maximum deuteron energy was measured to be 4.5 MeV for the largest guide tube to beam radius ratio. An increasing average ion energy with an increasing radius ratio was also observed.