Gyrotron Developments at Varian and Topics for Further Development

Cyclotron resonance coupling between microwave fields and an electron beam in vacuum is the basis for a family of microwave generators. This type of coupling has the advantage that both the beam and the associated microwave structures can have dimensions large compared to a wavelength. This allows the generation of orders of magnitude higher power output at a given wavelength than can be produced with conventional microwave tubes. The microwave interaction circuit can take the form of a single resonant cavity. This results in an oscillator device which has been called a gyrotron (1), (2). An amplifier can be made by using two cavities each operating below the oscillation threshold, where an input microwave signal is used to modulate the beam in one cavity and output power is removed from the modulated beam using the second cavity. By analogy this has been called a gyroklystron. Still another variation of cyclotron resonance coupling has been called a gyro traveling wave amplifier (gyro TWT). In that case a continuous waveguide is used for distributed interaction between the electron beam and a traveling wave.