A magnetron is a two-electrode valve in which the flow of electrons from a large central cathode to a cylindrical anode is controlled by crossed electric and magnetic fields; the electrons gyrate in the axial magnetic field, their energy being collected in a series of slot resonators in the face of the anode.

Magnetrons, used mainly as oscillators, can produce pulsed output at microwave frequencies, with high peak power ratings. Used as microwave and RADAR transmitters, and microwave ovens.