Low-noise operation and magnetic-priming of magnetrons by azimuthally-varying axial magnetic fields

A recent breakthrough at the University of Michigan has demonstrated that application of an azimuthally-varying axial magnetic field to a magnetron causes a dramatic reduction (-30 dB) in the microwave noise near the carrier and elimination of the sidebands (spurs). Another advantage of azimuthally-varying axial magnetic fields is "magnetic priming" in which the magnetron pi-mode oscillation-startup is hastened, especially when N/2 periods of magnetic perturbation are applied to an N-cavity magnetron. These experiments have been performed on kW microwave oven magnetrons. Computational simulations have also been performed in both 2-D and 3-D that verify the effects on rapid startup and noise observed experimentally.