Simulations of modulational and resistive instabilities in cylindrical crossed-field diodes

Summary form only given. Modulational and resistive instabilities in planar crossed-field diodes has been discovered and analyzed. It was noticed that in planar anode-cathode gaps in which the applied magnetic field was above cutoff (i.e. B>B/sub H/), steady cycloidal electron flow in the gap was violently unstable to the application of a small AC voltage perturbation. This phenomenon occurs over a wide band of frequencies and is caused by the formation of virtual cathode immediately in front of the cathode. A resistive instability in the crossed-field cycloidal electron equilibria was also found wherein energy dissipation in an external resistor triggered an instability in the flow which leads, again to the formation of a virtual cathode.