Nonlinear Research Of Coaxial-Waveguide Cyclotron Autoresonance Maser (CARM) Amplifier

High power sources in a range of millimeter and submillimeter waves have a great prospect of applications to radar, plasma heating, high-energy heating, communication, and therefore attract considerable attention in many countries. The devices based on the mechanism of electron cyclotron maser(ECM)-cyclotron autoresonance maser (CARM)-have the potential of high power and high efficiency for maintaining the resonance for a long distance. For this advantage, considerable work about it is taken theoretically, experimentally, and by computer simulation. Great progress is achieved. With the power increasing, the wall loss of the devices becomes a problem; meanwhile, the diameter of designed waveguide is too small to construct. A method to overcome both two difficulties is to use the larger waveguide, and it requires operation in high-order modes, where the mode spectrum is dense and mode competition could prevent the devices from stable single-mode operation. To get around the problem, one of the methods is to employ the coaxial cavities. The insertion of an inner rod into the waveguide can rarefy the spectrum of the competing modes in the vicinity of the operating mode and restrict the mode competing effectively. This type of device is the main object in this paper-coaxial-waveguide CARM amplifier.At first, starting from general wave equation, a self-consistent nonlinear theoretical model for a cylindrical waveguide CARM amplifier is presented. This model can describe the mutual interaction between wave and beam. Based on the model, a code of nonlinear beam-wave interaction in the CARM amplifier has been made. We use this code to simulate the experiment achieved in Mashachusetts Institute of Technology (MIT). With the condition of wiggler and no wiggler, the result is agreeable with the paper. So the code is proved to be reliable.The theoretical model of coaxial-waveguide CARM amplifier is also formed. In the base of the former work, the corresponding code is made. According to the parameters obtained by the linear theory, the TE28,16, 140GHz coaxial CARM amplifier has been simulated. The result suppliesthe conclusion from the linear theory. Further, the influence of the electron beam guide center radius, accelerated voltage, longitudinal guide magnet, beam current on the interaction efficiency is analyzed. After parameters are optimized, the saturated power is 679.06 kW, with the efficiency 14.9%. With the optimized parameters, the influence of the velocity spread on the performance is considered. The result shows that the spread can induce the considerable decreasing of the output power. The 1.5% spread causes the saturated power to fall to about 300 kW.