3D ICEPIC simulations of pulsed relativistic magnetron with transparent cathode : a comparative study with 3D MAGIC simulations

Ongoing research at the University of New Mexico (UNM) shows significant improvement in the start time and rate of build-up of microwave oscillations in a relativistic magnetron that uses a transparent cathode. In recent studies conducted at UNM the experimental results and the results of numerical simulations using the 3-dimensional particle-in-cell (PIC) code MAGIC have shown strong correlation. For this research a 3-dimensional PIC code ICEPIC developed at the Air Force Research Laboratory (AFRL) was used to simulate the A6 magnetron geometry with a transparent cathode. The results were compared with the work done at UNM to test the fidelity of the two simulation codes. Output parameters such as microwave power, microwave frequency, anode current, and leakage current with respect to the axial magnetic field were compared. ICEPIC simulations were run on a parallel architecture with 64 CPUs at a grid resolution of 1mmx 1mmy 1mmz in the 3-dimensional Cartesian coordinate system. These simulations consisted of roughly 6 million active grid cells and 16 million particles. Results indicated agreement between results from ICEPIC and MAGIC to within 20% for standard performance parameters. ICEPIC simulations also confirmed oscillation of the A6 magnetron with transparent cathode at 4 GHz in the 2\u03c0-mode

Fast start of oscillations in a short-pulse relativistic magnetron driven by a transparent cathode.

The magnetron has been a major component of radar systems since its introduction in World War II. The newer radar techniques require high peak power (GW) and short microwave pulses (few ns). To serve as a microwave source for short-pulse applications it is imperative that the magnetron needs to have both fast start and fast rate of build-up of oscillations. Both of these factors are contingent on the cathode geometry. The transparent cathode was invented at the University of New Mexico in an endeavor to improve the start time and increase the rate of build-up of oscillations in short-pulse relativistic magnetrons. The construction of the transparent cathode involves the removal of longitudinal strips of material from a hollow cathode. The resultant geometry has manifold advantages the first and the foremost of which is that it makes the cathode transparent to E_theta, thereby greatly increasing its amplitude where electrons are emitted. Hence one would expect faster rate of build-up of oscillations. Secondly, this geometry simultaneously gives rise to several different forms of priming: cathode priming, electrostatic priming and magnetic priming. The number of cathode strips is chosen so that it would excite a particular mode of interest (e.g. 6 strips would favor the formation of 6 spokes). The cathode strips may be oriented azimuthally in a manner that the electron bunches from the cathode strips would be released into the favorable phase of the mode of interest where efficient exchange of energy between the electrons and the RF fields could take place. The highlights of this dissertation are proof-of-concept computer simulations demonstrating the benefits of the transparent cathode in an A6 magnetron driven by a transparent cathode that have validated the simulations