Simulation of a rising sun magnetron employing a faceted cathode with a continuous current source

Abstract

It has been proposed that gated field emitters could be used in place of conventional thermionic cathodes to control the current injection in a magnetron, both temporally and spatially. Since gated field emitters have to be fabricated on flat surfaces, a faceted cathode would be used to implement this approach. A 2D ten cavity, rising sun magnetron has been modeled using the particle-in-cell code VORPAL. Cylindrical, five-sided, and ten-sided faceted cathodes were modeled to study the variation of magnetron operation due to the cathode shape. This work shows the results of the device performance employing three different cathode geometries with a typical continuous current source. The cathode voltage is -22.2 kV; magnetic field is 0.09 T; and linear current density is 326 A/m. The three models oscillated at the pi-mode, at a frequency of 960 MHz for the cylindrical cathode and 957 MHz for the faceted cathodes. Simulations show a faster start up time for the ten-sided faceted cathode. This resulted in a reduced overall startup time of the device from 200 to 110 ns. A strong current instability was observed in the five-sided cathode case with a periodicity range from 250 to 350 ns. This instability was limited to the start-up period of the ten-sided cathode model; hence the ten-sided case was more stable.