Prospects for Long Pulse Generation in a Magnetron using a Transparent Cathode

Summary form only given. The gap between the cathode and anode in a relativistic magnetron is, as a rule, much smaller than the radii of the electrodes in order to provide synchronous interaction between the electrons and the operating wave. However, the inadvertent production of plasma on the cathode during explosive electron emission quickly fills the anode-cathode (A-K) gap, thereby limiting the time of interaction. By using a transparent cathode, it is possible to increase the gap distance several times and facilitate longer pulse operation. In the transparent cathode, longitudinal strips are removed from a thin-walled tubular cathode, thereby increasing the amplitude of the synchronous azimuthal electric field in the electron flow region. As an example, computer simulations using the particle-in-cell code MAGIC of an A6 relativistic magnetron with 18 cathode strips show that the gap distance can be increased by a factor of three without significant degradation in the output characteristics. In addition to the possibility of larger gap spacings, a novel feature of the transparent cathode is that plasma can now propagate in both radial directions, unlike the case of a traditional solid cathode, where plasma can allow to propagate toward the interaction region. Simulation results, as well as plans for experiments, will be presented.