Low-noise, crossed-field devices such as a microwave magnetron having an azimuthally-varying axial magnetic field and microwave oven utilizing same

A microwave oven comprising:

• a compartment;
• and
• a low-noise, oven magnetron for generating microwaves in the compartment, the magnetron including:
• an electrical circuit for generating a radial electrical field, the circuit including a-cathode for emitting electrons and an anode having a number of resonant cavities wherein the cathode and the anode define an interaction space therebetween;
• and
• a magnetic circuit for generating an axial magnetic field substantially perpendicular to the radial electrical field in the interaction space wherein interactions between electrons emitted from the cathode and the electric and magnetic fields produce a series of space-charge spokes that travel around the space in an azimuthal direction and wherein the magnetic circuit includes at least one permanent perturbing magnet having an azimuthally varying magnetic field impressed thereupon so that the axial magnetic field is azimuthally varying in the interaction space to substantially eliminate microwave noise.

A microwave oven comprising:

• a compartment;
• and
• a low-noise, oven magnetron for generating microwaves in the compartment, the magnetron including:
• an electrical circuit for generating a radial electrical field, the circuit including a cathode for emitting electrons and an anode having a number of resonant cavities wherein the cathode and the anode define an interaction space therebetween;
• and
• a magnetic circuit for generating an axial magnetic field substantially perpendicular to the radial electrical field in the interaction space wherein interactions between electrons emitted from the cathode and the electric and magnetic fields produce a series of space-charge spokes that travel around the space in an azimuthal direction and wherein the axial magnetic field has a number of periods of perturbations in the azimuthal direction in the interaction space based on the number of resonant cavities to substantially eliminate microwave noise and shorten start-up time of the magnetron.