Theoretical Analysis And Numerical Simulation Of A Coaxial Vircator With Enhanced Modulation

The coaxial vircator has a good application prospect because of its virtues of relative higher efficiency, frequency-stable output and the long pulse operability compared with the traditional vircator. However, the poor power conversion efficiency still impedes its development. In order to realize its practical goal, the effect of the modulation of the electron beam on the power conversion efficiency is studied theoretically and numerically, which lays a foundation for the design of the coaxial vircator with premodulation.Based on one-dimensional and steady-state hypotheses, a simple physical model of a coaxial vircator is established initially to give the microwave gain of the nonlinear resonance between the injected electron beam and the oscillating E-field inside the interacting cavity and the nonlinear beam-wave interaction process is also discussed in depth. The effect of injected beam premodulation on the power efficiency is analyzed theoretically according to the model and the validity of the theoretical predictions is test by the numerical simulation, which indicates that modulation enhancement can be used as one of the most effective way to increase the power efficiency. In addition, with the modulation process in a coaxial modulating cavity analyzed, a one-dimensional model for the interaction between the TEM mode and the intense electron beam is also set up to study the effect of the intensity of the E-field inside the modulating cavity, the numbers of the cavities and the gap width of the cavity on the modulation amplitude, from which the two methods of modulation enhancement, namely introducing a multi-cavity modulation structure and increasing the intensity of the E-field inside the cavity, is obtained.To test the validity of the above theoretical analysis, a coaxial vircator with radial three-cavity premodulation and a coaxial vircator with improved dual-cavity modulation are proposed and studied numerically. With the optimization of the former, a high power of 7.20 GW is obtained with the power efficiency of 20%. In regards to the latter, a output power of 7.05 GW can be achieved with an efficiency of 19.6%. The numerical results show that the increased modulation of the e-beam has important significance in increase the power efficiency.