Suppression of leakage current in a relativistic magnetron using a novel cathode endcap design

Upcoming experimental verification of MAGIC particle-in-cell (PIC) code simulation of a high-power, 70%-efficient relativistic magnetron with diffraction output (MDO) requires leakage electrons to be insulated axially from a dielectric antenna window [1]. Endcaps in relativistic magnetron systems have been explored before with great success in increasing output power and efficiency and greatly reducing leakage current, but none has yet to completely suppress leakage current [2, 3]. In our experiments the radius of a disk endcap was extended slightly beyond the inner radius of an A6 anode slow-wave structure, such that electrons from the interaction space drifting downstream along the axial magnetic field lines are stopped. On the endcap surface, which is not bombarded by these electrons, a thin dielectric coating was added to lower the endcap surface electric fields and to capture any emitted electrons. Preliminary results of experiments on a radial-extraction relativistic A6 magnetron system (260 kV, 16 ns paraboloidal pulse) with a solid cathode almost entirely suppressed the leakage current. Extension of these experimental results through MAGIC will provide a predictive mechanism for the success of endcap designs in the MDO system.