Suppression of Leakage Current in a Relativistic Magnetron Using a Novel Design Cathode Endcap

In relativistic magnetrons, explosive electron emission cathodes are typically used to generate the electron flow in the crossed field between the coaxial electrodes. Electrons that axially leave the interaction space and the cathode edge reduce magnetron efficiency, which can lead to window breakdown when axial microwave extraction is used, e.g., a magnetron with diffraction output. Because of this, numerous publications have been devoted to different solutions of decreasing the leakage current and protecting the dielectric window from electron bombardment. In this paper, we present the results of our initial experiments to suppress leakage current in the well-known A6 magnetron using a thin dielectric coating on a cathode endcap that is extended downstream of the interaction space in a uniform magnetic field. We found that using a relatively thin dielectric coating on a polished graphite endcap with radius that extends beyond the cathode radius decreased the leakage current from over 1 kA down to about 10 A.