Plasma wake‐field effects on high‐current relativistic electron beam transport in the ion‐focused regime

Modulation of the beam current has recently been observed during ion‐focused regime (IFR) transport of a high‐power relativistic electron beam propagating through a low‐density background plasma. Injecting a high‐current, high‐energy electron beam into an IFR channel immersed in a background plasma induces plasma oscillations. These background plasma oscillations, induced by the rise‐time portion of the beam ejecting plasma electrons from the vicinity of the beam into the background plasma, give rise to a modulated axial electric field. This field travels with the beam leading to beam energy and current oscillations. In the experiment, a 1.7 MeV, 1 kA, rise‐time‐sharpened electron beam is propagated on a KrF excimer laser‐produced IFR channel in trimethylamine (TMA) gas, which is immersed in a low‐density plasma‐filled transport tube. Experimental measurements, analytical theory, and detailed computer simulations are presented demonstrating modulation of this high‐current relativistic electron beam near the low‐density background plasma frequency.