Simulation of a faceted magnetron using discrete modulated current sources

Summary form only given. Simulation of a 2-D model of a ten cavity rising sun magnetron was developed using the 3-D particle-in-cell (PIC) code VORPAL 5.2¹. The cathode structure is comprised of field emitters, designed with facet plates with slits to protect the emitters². A cylindrical and faceted (five and ten sided) cathode was modeled to study the variation of results due to the cathode shape. Discrete current sources were modeled to come from each facet of the five and ten sided cathode to study its effect on the magnetron operation. Each plate on the five sided cathode structure contains 5 emitters that can be addressed spatially and modulated temporally. Similarly the ten sided cathode contains 3 emitters per facet. The simulations were run with the discrete current sources and then compared with the reference continuous current source model. The discrete current sources allow control in space and time of the current injection. Each ON emitter represents the location of the electron spoke. By using this technique, the startup of oscillations and its location can be controlled. Simulations demonstrating this concept are presented in this work. This technique was implemented in both the five sided and ten sided cathode structure. Startup times from each model were obtained from the simulation. The ten sided, modulated cathode resulted in the fastest start up at 35 ns. After analyzing each model, it was found that there is an instability in the five sided cathode oscillations. This instability results in a current “spike” to the anode and a subsequent collapse of the spokes. An analysis of the total current injected was completed to address this problem. This was observed in both the continuous and the modulated current source models. The problem was minimized by implementing the ten sided cathode geometry. These results and comparisons will be presented in this work. Finally, by using the modulation technique, a phase shi- t of 180° was simulated by changing the timing of the modulated current injection. This work and additional observations will be also presented.