Radiation of linear waves by solitons in a Josephson transmission line with dispersion

We report a method of using a distributed Josephson junction to generate and amplify electromagnetic waves, based on Cherenkov radiation of linear waves by Josephson solitons. The device by which this principle can be realized is essentially a distributed Josephson junction electromagnetically coupled to a dispersion waveguide system providing resonance interaction between moving solitons and a linear electromagnetic wave. The current-induced motion of Josephson vortices in a distributed junction excites, due to the Cherenkov effect, a synchronous electromagnetic wave in the dispersion line; by interacting with the radiation field the vortices bunch in the decelerating phase of the wave, thus providing the coherence contribution of a large number of solitons to radiation. These devices are actually the Josephson analog of the traveling-wave and the backward-wave tubes. A linear theory for these types of oscillators and amplifiers is developed, and the equations for the starting current and growth rate of instability are obtained. A study performed on the nonlinear effects has yielded straightforward estimates of the generation power.