Simulation of a phase controlled magnetron using a modulated, addressabel cathode

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. A 10-sided cathode structure was modeled to represent gated field emitters on the facet plates². Each plate contains 3 emitters that can be addressed spatially and modulated temporally. The simulations were initially run to compare a cylindrical, 5-sided, and 10-sided cathode with continuous current emission (DC). Then the simulations were run with the modulated electron sources. For the rising sun magnetron, the π-mode is the primary mode, so the 10 cavity device has 5 spokes in π-mode. Therefore, a single spoke rotates past 2 cathode facet plates (6 total emitters) every RF period. This magnetron oscillates at 957 MHz. Hence, 1 out of 6 emitters per 2 adjacent facets was turned on at a frequency of 957 MHz with a 1/6 duty cycle. Therefore, 5 emitters are on at one time for the entire magnetron; each ON emitter represents the location of the electron spoke. This approach then controls the startup of oscillation and location of the spokes (phase). Simulations demonstrate this effect. A decreased start-up time is observed, falling from 100 ns for the continuous current source cases to 35 ns using modulation. The spokes are always located at the same locations in simulation time for different simulations runs while without source modulation control, the spoke locations vary randomly. Finally, during a simulation run, the spoke locations were shifted by 180° by changing the timing of the modulated current injection to generate the electron spokes 180° out of phase. This demonstration of phase control as well as other observations from the simulations will be presented.