Autoacceleration via Virtual Cathode Oscillation

Injection of monoenergetic electron beams with uniform number density into an evacuated, straight-walled, equipotential cylindrical drift tubes has been modeled. An oscillating virtual cathode is produced by having the injected current exceed the space-charge limiting current of the drift tube. If the oscillation frequency of the virtual cathode exceeds the local beam plasma frequency a coherent traveling EM wave is launched with electric fields on the order of MeV/cm for an injected beam density of 1012 cm-3. Furthermore, in the absence of a strong axial magnetic field transmitted particles are autoaccelerated up to 3 times their initial kinetic energy.