Magnetic priming effects on noise, startup, and mode competition in magnetrons

Azimuthally varying axial magnetic fields have been utilized to perform "magnetic priming" of magnetrons for rapid startup, low noise, and mode control. An overview of the latest magnetic priming experimental and simulation results are presented in this paper. Magnetic priming experiments in dc-operating microwave oven magnetrons show sideband elimination, even with the cathode heater turned off. Simulations using three three-dimensional (3-D) improved concurrent electromagnetic particle-in-cell (ICEPIC) codes with two different computational algorithms recover the oven magnetron experimental results obtained with magnetic priming including fast mode growth, rapid spoke formation, and the tendency toward lower noise operation. A new, axially symmetric, azimuthally varying magnetic field geometry for oven magnetrons is explored and preliminary results are reported. Simulations using two-dimensional (2-D) MAGIC code for the University of Michigan/Titan relativistic magnetron show that the oscillation startup time can be dramatically decreased (almost by a factor of 3) and mode competition can be suppressed with magnetic priming.