Klystron

A klystron is a specialized linear-beam vacuum tube (evacuated electron tube). The brothers Russell and Sigurd Varian of Stanford University are generally considered to be the inventors of the klystron. Their prototype was completed in August 1937 [5].

Klystrons are used as an oscillator or amplifier at microwave and radio frequencies to produce high-power carrier waves and the driving force for linear accelerators. Many klystrons have a waveguide for coupling microwave energy into and out of the device, although it is also quite common for lower power and lower frequency klystrons to use coaxial couplings instead. In some cases a coupling probe is used to couple the microwave energy from a klystron into a separate external waveguide.

In the two-chamber klystron, an electron beam from the cathode of an electron gun is injected into a resonant cavity we just discussed in the previous sections (see reentrant cavity). The electron beam is constrained by an axial magnetic field and is accelerated by a positive potential into a connecting passage (called a drift tube) to a second resonant chamber containing a positively charged anode. While passing through the first cavity, the electron beam is velocity modulated (periodically bunched) by the weak RF signal. In the moving frame of the electron beam, the velocity modulation is equivalent to a plasma oscillation, so in a quarter of one period of the plasma frequency, the velocity modulation is converted to density modulation, i.e. bunches of electrons. As the bunched electrons enter the second chamber they induce standing waves at the same frequency as the input signal. The signal induced in the second chamber is much stronger than that in the first.