Search

The generation of annular relativistic electron beams (AREBs) with a good uniformity and longitudinal consistency needs intensive investigations, especially when no guiding magnetic field is supplied. Without a guiding magnetic field, ring-shaped cathodes with a width of several millimeters were utilized to generate AREB instead of knife-edged cathodes because of the space-charge force. Results of the fast framing optical photograph experiments and high power microwave (HPM) experiments show that the quarter-circular shielding electrode can improve the uniformity of the AREB obviously, and the carbon fiber cathode is validated to be an appropriate choice, which showed better emission characteristics and better performance in generating HPM than the graphite cathode and the polymer velvet cathode. [ABSTRACT FROM AUTHOR]

Unlike planar diodes, separate research of the axial and radial plasma expansion velocities is difficult for magnetically insulated coaxial diodes. Time-resolved electrical diagnostic which is based on the voltage-ampere characteristics has been employed to study the temporal evolution of the axial and radial cathode plasma expansion velocities in a long pulsed magnetically insulated coaxial diode. Different from a planar diode with a “U” shaped profile of temporal velocity evolution, the temporal evolution trend of the axial expansion velocity is proved to be a “V” shaped profile. Apart from the suppression on the radial expansion velocity, the strong magnetic field is also conducive to slowing down the axial expansion velocity. Compared with the ordinary graphite cathode, the carbon velvet and graphite composite cathode showed superior characteristics as judged by the low plasma expansion velocity and long-term electrical stability as a promising result for applications where long-pulsed and reliable operation at high power is required. [ABSTRACT FROM AUTHOR]