Particle-in-cell simulation of an industrial magnetron with electron population analysis

Abstract

Results from a particle-in-cell simulation study of L3Harris CWM-75 kW are presented; the continuous wave cooker magnetron typically operates at 18 kV, 5 A, 1900 G, 896–929 MHz. The startup process of the device has been simulated in 3D by using the PIC code VSim. The startup behavior was examined with (1) no priming, (2) RF priming, and (3) cathode modulation. Under no priming, the simulated device failed to oscillate in a simulation time of 1000 ns. Oscillations were achieved with both RF priming (150 ns) and cathode modulation (180 ns). Half (∼40 kW) of the device’s typical operating power at a frequency of 915 MHz, the device’s π-mode frequency, was used for the RF priming, and the priming was active only during the first 50 ns of the simulation. The device then oscillated later, but oscillation soon failed as the spokes collapsed. Continuous cathode modulation was also performed at 915 MHz with stable oscillation after 180 ns. A method for analyzing the electron device physics during the magnetron startup was developed by examining time-dependent particle distribution profiles in r and φ. These results provide insight into the conditions in the electron hub that lead to oscillation, particularly the azimuthal velocity distribution where the distribution shows a clear low or negative velocity prior to the start of oscillation.