We give a model for the impedance behavior of a relativistic electron beam diode of ring shape. The diode consists of a double emitter annular cathode: the two emitters are separated by a well to avoid fast plasma closure, opposite to a flat anode plate. It is connected via a triplate vacuum feed to the waterline of a pulsed power machine. We use the concept of magnetic limiting to show that the emitters influence each other magnetically, and give their impedance as a function of emitter voltage, geometry, and the current flowing from one emitter to the other. We also show that under certain circumstances, in which the emitter voltages differ from each other, that magnetic shutoff of one of them by the other can occur in timescales tgr;sim;lgr;/Z, where lgr; is the vacuum inductance of the well,Vthe dominant emitter voltage, andZits impedannce. We give a pertinent numerical example and comment on posible measures to avoid this dominance.
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