klystron

klystron: see electron tube.

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klystron

A type of vacuum tube used as an amplifier and/or oscillator for UHF and microwave signals. It is typically used as a high-power frequency source in such applications as particle accelerators, UHF TV transmission and satellite earth stations. The klystron was invented at Stanford University in 1937 and originally used as the oscillator in radar receivers during World War II.

A klystron tube makes use of speed-controlled streams of electrons that pass through a resonating cavity. Electrons in a klystron are accelerated to a controlled speed by the application of several hundred volts. As the electrons leave the heated cathode of the tube, they are directed through a narrow gap into a resonating chamber, where they are acted upon by an RF signal. The electrons bunch together and are directed into one or more additional chambers that are tuned at or near the tube's operating frequency. Strong RF fields are induced in the chambers as the electron bunches give up energy. These fields are ultimately collected at the output resonating chamber. See magnetron and diode.

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klystron [′klī‚strän]

(electronics)

An evacuated electron-beam tube in which an initial velocity modulation imparted to electrons in the beam results subsequently in density modulation of the beam; used as an amplifier in the microwave region or as an oscillator.

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Klystron

An evacuated electron-beam tube in which an initial velocity modulation imparted to electrons in the beam results subsequently in density modulation of the beam. A klystron is used either as an amplifier in the microwave region or as an oscillator.

For use as an amplifier, a klystron receives microwave energy at an input cavity through which the electron beam passes. The microwave energy modulates the velocities of electrons in the beam, which then enters a drift space. Here the faster electrons overtake the slower to form bunches. In this manner, the uniform current density of the initial beam is converted to an alternating current. The bunched beam with its significant component of alternating current then passes through an output cavity to which the beam transfers its ac energy.

Klystrons may be operated as oscillators by feeding some of the output back into the input circuit. More widely used is the reflex oscillator in which the electron beam itself provides the feedback. The beam is focused through a cavity and is velocity-modulated there, as in the amplifier. The cavity usually has grids to concentrate the electric field in a short space so that the field can interact with a slow, low-voltage electron beam. Leaving the cavity, the beam enters a region of dc electric field opposing its motion, produced by a reflector electrode operating at a potential negative with respect to the cathode. The electrons do not have enough energy to reach the electrode, but are reflected in space and return to pass through the cavity again. The points of reflection are determined by electron velocities, the faster electrons going farther against the field and hence taking longer to get back than the slower ones. Reflex oscillators are used as signal sources from 3 to 200 GHz. They are also used as the transmitter tubes in line-of-sight radio relay systems and in low-power radars.