Particle-in-Cell (PIC) Simulation of CW Industrial Heating Magnetron

Abstract

Modern CW industrial heating magnetrons are capable for producing as high as 300 kW of continuous-wave microwave power at frequencies around 900 MHz and are sold commercially [Wynn et al., 2004]. However, to utilize these magnetrons in some specific research and scientific applications being of interest for the Air Force, the necessary adaptation and redesign are required. It means that the detailed knowledge of principles of their operation and full understanding of how the changes of the design parameters affect their operational characteristics are necessary. We have developed and tested computer model of a 10-vane high-power strapped magnetron, which geometrical dimensions and design parameters are close to those of the California Tube Laboratory's commercially produced CWM-75/100L tube. The computer model is built by using the 3-D Improved Concurrent Electromagnetic Particle-in-Cell (ICEPIC) code. Simulations of the strapped magnetron operation are performed and the following operational characteristics are obtained during the simulation: frequency and mode of magnetron oscillations, output microwave power and efficiency of magnetron operation, anode current and anode-cathode voltage dynamics. The developed computer model of a non-relativistic high-power strapped magnetron may be used by the industrial magnetron community for designing following generations of the CW industrial heating high-power magnetrons.

Stimulated Generation of Magnetrons powered below the Self-Excitation Threshold Voltage

“…Typical current density emitted by the tungsten cathodes is about of 0.3 A/cm 2 in the industrial magnetrons [15] which requires the cathode temperature of about 2500 K. Operation of the cathode at such high temperature and the cathode additional overheating caused by electron back-stream worsen the vacuum in the cathode vicinity approximately by an order of magnitude. In the cold magnetron the vacuum pressure is typically about 10 -6 torr, while during tube operation the average vacuum pressure in the space of interaction is ~5•10 -6 torr.…”

“…For the commercial 100 kW, 920 MHz magnetron [15] the probability to create an ion on the length of Larmor orbit is 3.8•10 -5 . For the emitted current of ~ 6 A the ion flux is ~5•10 14 ions/s, i.e., the flux density of ions hitting the cathode is about of 7.2•10 13 ions/cm 2 •s with the average ion energy of ~10 keV.…”

Magnetron High Power System Design

“…Several studies and different simulation strategies have been performed on the DW [8][9][10][11] and Magnetron [12][13][14][15][16] technologies, however we propose to consider the relationships between thermo-mechanical effects and electromagnetic behavior of such devices.…”