magnetron

A magnetron is a high-powered vacuum tube that generates microwaves by the interaction of a stream of electrons with a magnetic field in a resonant cavity. It consists of a heated cathode, an anode block with resonant cavities, and a magnetic circuit that provides a perpendicular field.

When operated, electrons emitted by the cathode are accelerated toward the anode. The magnetic field causes the electrons to move in curved paths, transferring energy to the RF fields of the cavities. The microwaves are extracted from the tube via an output waveguide or antenna.

The resonant frequency is set by the cavity geometry, placing most devices in the microwave range, typically 1 to 30 GHz. Domestic microwave ovens use a cavity magnetron near 2.45 GHz with several kilowatts of peak power.

The cavity magnetron was developed in 1940 by John Randall and Harry Boot at the University of Birmingham, contributing to the Allies' radar capabilities during World War II. Since then magnetrons have become a common microwave source for radar, cooking, and industrial heating.

Modern systems sometimes use solid-state sources for microwave generation, but magnetrons remain economical for high-power applications. Safety concerns include high voltage operation and exposure to microwaves, requiring proper shielding and interlocks.