Active circulator gyrotron traveling-wave amplifier

An RF cyclotron maser type traveling-wave amplifier including an integral active circulator is described. It includes a tapered interaction waveguide having a cross-section which gradually increases from a small first end to a larger second end. The waveguide is capable of supporting first and second orthogonal polarization modes with approximately the same propagation characteristics for the two modes. A beam of mildly relativistic electrons having helical electron motion is directed into the small first end to axially propagate within the waveguide toward the larger second end. A tapered magnetic field is generated within the waveguide in a direction approximately parallel to the axis of the waveguide. An input electromagnetic wave in the first polarization mode is launched into the larger second end of the waveguide to propagate toward the first end. The input wave is reflected by the constriction of the tapered waveguide to propagate with the electron beam in the waveguide. The reflected input wave additionally excites energy in the second mode which also co-propagates with the electron beam. The first and second modes are amplified by the electron beam; the second polarization mode being amplified to a greater extent than the first mode. The two orthogonal modes are easily separated to provide input and output ports for the amplifier.