gyrotron is the high-power microwave source used for electron cyclotron heating — a vacuum electron tube that converts beam energy into megawatt-scale microwave output.
The device runs on the same physics it feeds. Inside a gyrotron, an electron beam gyrates in a strong magnetic field, and that rotation is coaxed into radiating coherently at the cyclotron frequency — the maser principle applied to spiraling electrons. The result is a tube that produces continuous megawatt power at frequencies above 100 gigahertz, a regime conventional microwave tubes such as klystrons cannot reach at that power. Soviet physicists developed the gyrotron in the 1960s, and 📝fusion has been its driving application ever since: ITER's 📝electron cyclotron resonance heating (ECRH) system uses 1-megawatt gyrotrons with pulse lengths beyond 500 seconds at 170 gigahertz.
What separates a gyrotron from the transmitters behind 📝ion cyclotron resonance heating (ICRH) is the frequency gap: ion heating needs tens of megahertz, reachable with radio-broadcast-class tetrodes, while electron heating needs a thousand times higher frequency, and only the gyrotron delivers it at fusion power levels. Gyrotron performance — unit power, efficiency, and reliability — therefore sets the practical ceiling on how much ECRH a machine can field, making the tube one of the enabling technologies of 📝plasma heating and control.