The gyrotron is a type of free-electron maser which generates high-frequency electromagnetic radiation by stimulated cyclotron resonance of electrons moving through a strong magnetic field.[4][5] It can produce high power at millimeter wavelengths because as a fast-wave device its dimensions can be much larger than the wavelength of the radiation. This is unlike conventional microwave vacuum tubes such as klystrons and magnetrons, in which the wavelength is determined by a single-mode resonant cavity, a slow-wave structure, and thus as operating frequencies increase, the resonant cavity structures must decrease in size, which limits their power-handling capability.