Propagation of an Intense Relativistic Electron Beam through a Plasma Region into Vacuum

An intense relativistic electron beam (IREB) is injected through a narrow plasma region into a vacuum drift tube at current levels far above the space‐charge limit of the drift tube. Experiments show that accelerated co‐moving positive ions from the plasma enable the beam to propagate to a collector at the end of the 15 cm diameter drift tube. In one set of experiments, the IREB (1 MeV, 27 kA, 30 nsec) passes through a hydrogen gas cloud with an effective width of approximately 2 cm. The net current measured by a 7 cm diameter collector at the end of a 55 cm long drift tube is 70% of the peak injected electron current. In another configuration, the IREB is injected through a laser‐produced carbon plasma. A model is proposed linking electron beam propagation with collective ion acceleration which results in the generation of charge‐ and current‐neutral plasmoids capable of free space propagation. Possible implications of this work to astrophysical processes (cosmic ray acceleration) and laser fusion (observation of high‐energy positive ions escaping from target plasma) are discussed.