Drawing of a magnetron, a vacuum tube used as an oscillator to generate microwaves at high power levels, used in radar sets and microwave ovens, from a 1984 Naval training text. The tube is shown with part of the copper anode block cut away, revealing the cathode and cavity resonators. The magnetron shown here is several decades old, and uses two alnico horseshoe magnets. Modern magnetrons use more compact rare earth magnets.