Producing a magnetized low energy, high electron charge density state using a split cathode

Abstract

When a magnetized annular relativistic electron beam propagating in a conducting tube carries a charge higher than the space charge limit, it can stabilize at a lower energy and higher density state. Such a charge distribution can be used as an electron source in high power microwave devices, a relativistic magnetron in particular, and in other applications. The limiting current transmitted by the beam decreases in tubes with larger radii, so in a tube with a radial transition from a small to large radius, the current can over-inject the downstream tube. This can start a dynamical process which stabilizes as a high density state. The same effect can be achieved by increasing the magnetic field in a magnetic mirror-like scheme or by adding a slowing down potential in the electron beam's route. Here, we propose a simpler, more practical way to produce such a dense state by splitting the cathode into an emitter and a reflector. This scheme is tested in simulation and experiment.