Radial oscillation of intense relativistic electron beam in low-magnetic-field foil-less diode

The radial oscillation of an intense relativistic electron beam possesses two main features of the spatial period and the radial oscillation amplitude in a low-magnetic-field foil-less diode, and the large radial oscillation extremely limits the beam–wave conversion efficiency and stability of a high-power microwave device. Thus, the formation mechanism of the radial oscillation is analyzed in detail. The results show that the radial oscillation of an electron beam consists of a great number of electrons with different Larmor radii and guiding centers, and the large radial oscillation is mainly caused by the strong radial electric field and the directional difference between the electric field and the magnetic field in the anode–cathode gap. A low diode voltage or a proper large anode radius is beneficial to improve the beam quality. Considering that cathode plasmas have a dominant effect on the spatial distribution of electrons, the explosive emission model was improved with cathode plasmas, and the consistency between simulation and experimental results becomes better.