Influence of ion channel on electron beam propagation

The electron beam propagation from a gas-filled diode is investigated. The beginning portion of the electron beam pulse creates an ion channel not only inside the diode but also the region beyond the anode. A theoretical model is developed for a space-charge limited current of a relativistic electron beam propagating through an ion channel. A simple analytical expression of the space-charge limited current is obtained within the context of a thin beam approximation, where the conducting tube radius is much larger than the beam radius. Beam current propagating through an ion channel is measured experimentally for a mildly relativistic electron beam. Whenever the ion density inside a diode is the same as the beam electron density, the diode is short-circuited. The ion channel density at the short-circuiting time is numerically calculated and is used to estimate the space-charge limited current. It is shown that experimental data agree well with analytical results predicted by the theoretical model