TLDR: The cavity magnetron is a device that generates microwaves using a stream of electrons and a magnetic field. It was used in early radar systems and is now commonly found in microwave ovens.
The cavity magnetron is a special type of vacuum tube that was used in early radar systems and is still used today in microwave ovens and linear particle accelerators. It generates microwaves by using a stream of electrons and a magnetic field. The electrons pass by small cavities in a metal block, causing microwaves to oscillate within the cavities. This is similar to how a whistle produces a tone when air is blown past it. The frequency of the microwaves is determined by the size of the cavities. Unlike other vacuum tubes, the magnetron cannot amplify microwave signals, but it can generate a microwave signal from direct current electricity.
The development of the magnetron was influenced by the invention of the Audion, a device that controlled the flow of electric current using a grid. Researchers like Albert Hull and Hans Hollmann worked on improving the magnetron, but it was John Randall and Harry Boot who made a breakthrough in 1940 with the development of the cavity magnetron. Their design produced hundreds of watts of power at a wavelength of 10 cm, which was a significant achievement. The cavity magnetron allowed for the production of high-power microwave signals in a small device, revolutionizing radar systems during World War II. It gave the Allies a significant advantage over their enemies and played a crucial role in the outcome of the war.
The cavity magnetron works by using a heated cathode and an anode within an evacuated chamber. A magnetic field is applied parallel to the axis of the chamber. The electrons emitted from the cathode are attracted to the anode and follow a curved path due to the magnetic field. As the electrons pass by the cavities in the metal block, they induce a high-frequency radio field, causing the electrons to bunch into groups. Some of the radio frequency energy is extracted and directed to a waveguide, which can be connected to an antenna or used for heating purposes.
The magnetron has various applications, including radar systems, microwave ovens, and lighting systems. In radar, the magnetron's waveguide is connected to an antenna and produces short pulses of high-power microwave energy. This energy is used to detect and track objects. In microwave ovens, the magnetron generates microwaves that heat food by exciting water molecules. In lighting systems, the magnetron provides the microwave field that is passed through a waveguide to the lighting cavity, where it interacts with light-emitting substances.
The development of the cavity magnetron was a significant technological advancement that had a profound impact on various fields. It allowed for the production of high-power microwave signals in a compact device, enabling the development of advanced radar systems and microwave ovens. Today, the magnetron remains an essential component in many microwave applications.