Collective ion acceleration and intense electron beam propagation within an evacuated dielectric guide

Experiments were conducted to extend a previous study¹ of collective ion acceleration and electron beam propagation within an evacuated dielectric guide to higher beam energies. The typical electron beam injection conditions were as follows: current ∼ 65 kA, voltage ∼ 1.5 MV, ν/γ ∼ 1.4 and pulse duration ∼ 60 nsec. Beam propagation was found to depend upon space charge neutralization resulting from ions released from the walls of the dielectric guide. The primary energy loss mechanism was found to be erosion of the beam front. With a diode consisting of a small diameter cathode but no anode foil, protons with kinetic energies up to 14 MeV were detected on axis using nuclear activation techniques. The maximum observed yield was ∼ 10¹³ protons (E > 3.8 MeV).