Nonlinear Studies Of Multi-mode Cyclotron Autoresonance Maser

Cyclotron autoresonance maser (CARM) is a kind of high power electromagnetic wave sources, the operating mechanism of which is based on the electron cyclotron resonance radiation. Since the concept of CARM was proposed, it has been attracting much attention due to its prospective peculiarities such as relatively lower operating magnetic field, larger RF cross-sectional size, and weak relativistic electron beam). Although plenty of theoretical models have been performed for CARM in the past years, most of them mainly focused on the interaction of a single mode with the electron beam, and relatively less attention was paid to the multimode interaction. As the frequency of a CARM is stretched to terahertz (THz) or sub-THz wave ranges, higher-order mode is always adopted so as to enlarge the cross-sectional dimension of the cavity and then to facilitate the mechanic manufacture and thermal wall loading. However, it may also lead to severe over-modes and thus mode competition may happen. Consequently, multi-mode interaction should be considered in a THz or sub-THz CARM. Based on the single mode nonlinear model, a multimode nonlinear theory is proposed for CARM and the nonlinear interaction of multimodes with relativistic electron beam in a terahertz CARM is specially analyzed. The main work of this thesis includes:In Chapter 1, the operating principle and recent development of CARM are briefly introduced.In Chapter 2, a complete set of self-consistent equations describing the nonlinear interaction of multimodes with the relativistic electron beam in CARM is derived. These equations include the beam-wave coupling equations for TE mode coaxial CARM, TM mode coaxial CARM, TE mode cylindrical CARM, TM mode cylindrical CARM. The beam-wave coupling equations taking Ohmic losses into account and the motion equations for electron immerged in multimode electromagnetic waves are also derived.In Chapter 3, the key issues of computer code for the proposed multimode nonlinear theory are introduced, including normalization of quantities, choice of initial parameters, accuracy monitoring. Finally, the block diagram of software is presented and the computer codes are programmed in FORTRAN language. These codes can be employed for both the simulation of the whole interaction process of multimodes with the relativistic electron beam and the optimization of operating parameters.In Chapter 4, the multimode nonlinear theory and computer code are verified by the comparison of experimental and theoretical results which have been published. These verifications ensure the reliability of the results simulated in the next Chapters.In Chapter 5, a THz, high-order TE-mode CARM is analyzed by multimode nonlinear theory. The influences of operating parameters on multimode beam-wave interaction indicate that the performance of a high-order TE mode CARM deeply depend on the operating parameters, and thus it is necessary to perform multimode beam-wave interaction for parameter design.In Chapter 6, a THz, high-order TM-mode CARM is analyzed by multimode nonlinear theory. The feasibility of a THz CARM operated with TM mode is verified. The influences of operating parameters on multimode beam-wave interaction indicate that the performance of a high-order TM mode CARM deeply depend on the operating parameters, and thus it is necessary to perform multimode beam-wave interaction for parameter design.The proposed multimode nonlinear theory and computer codes can be employed to analyze the interaction of multimodes with relativistic electron beam in CARM. In addition, the potential mode competition in CARM can also be revealed by observing the influence of operating parameters on multimode beam-wave interaction and this will be benefit to the design and optimization of CARM operating parameters.