Propagation in Vacuum of an Intense Electron Beam Injected Through a Localized Plasma

Propagation of an intense relativistic electron beam (1 MeV, 27 kA, 30 ns) in vacuum after passage through a localized hydrogen plasma of {~} 2-cm width has been observed. A large fraction of the injected current was found to propagate in a vacuum drift tube to a distance in excess of 50 cm downstream of the plasma. A description of the process is proposed which links the electron beam propagation with collective ion acceleration and which relates to cosmic-ray acceleration and laser experiments.