Particle beam dynamics in a magnetically insulated coaxial diode

The dynamics of charged particle beams emitted from a cathode into a `smooth´ coaxial diode with magnetic insulation (MICD) is studied with the aid of 3-D simulation. The processes controlling space charge formation and its evolution in the MICD are modeled for the structure geometries typical of high-voltage millimeter wave magnetrons1 that are characterized by very high values of emission currents, hence high space charge densities. The beam particles that interact both with the space charge which they belong to, and with external dc electric and magnetic fields give rise to an azimuthal electron flow in the anode-cathode gap and to axially oriented flows outside that. In experiments with millimeter wavelength relativistic magnetrons1 the axial currents were identified as a major factor to negatively affect magnetron efficiency.