Internal structure of electron-beam filaments

Electron beams of tW/${\mathrm{cm}}^2$ (∼0.4 MeV) which are split into filaments are produced by an inductive generator which transfers field energy to beam particles in 1-10-ns pulses. Target-damage analysis reveals the composite internal structure of each filament as a sequence of concentric circles with a discontinuous pattern. The nonuniform distribution of collectively accelerated positive ions within a filament contributes to resolve the filament structure which propagates at a speed $\sim \frac{3c}{4}$ and can cross unaffected a ${10}^3$-G magnetic field.