Gyrotron

A gyrotron is a class of high-power linear-beam vacuum tubes that generates millimeter-wave electromagnetic waves by the cyclotron resonance of electrons in a strong magnetic field.

Output frequencies range from about 20 to 527 GHz,[1][2] covering wavelengths from microwave to the edge of the terahertz gap.

The gyrotron is a type of free-electron maser that generates high-frequency electromagnetic radiation by stimulated cyclotron resonance of electrons moving through a strong magnetic field.

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.

Thus, as operating frequencies increase, the resonant cavity structures must decrease in size, which limits their power-handling capability.

In the gyrotron, a hot filament in an electron gun (1) at one end of the tube emits an annular-shaped (hollow tubular) beam of electrons (6), which is accelerated by a high-voltage DC anode (10) and then travels through a large tubular resonant cavity structure (2) in a strong axial magnetic field, usually created by a superconducting magnet around the tube (8).

Due to the standing waves in the resonant cavity, the electrons become "bunched"; that is, their phase becomes coherent (synchronized), so they are all at the same point in their orbit at the same time.

The helical gyrotron electron beam can amplify an applied microwave signal similarly to the way a straight electron beam amplifies in classical microwave tubes such as the klystron, so there is a series of gyrotrons that function analogously to these tubes.

It generates oscillations traveling in an opposite direction to the electron beam, which is output at the upstream end of the tube.