An evacuated electron tube used as an oscillator or amplifier at microwave frequencies. In the klystron, an electron beam is velocity modulated (periodically bunched) to produce large amounts of power. The specialized linear-beam vacuum tube (evacuated electron tube) that amplifies radio frequency energy and provides the power to the Clinac linear accelerator and other very high-power applications. The klystron tube was invented by brothers Russell and Sigurd Varian.