Three Times In The Research Of Terahertz Harmonic Gyrotron

THz radiation (THz,1 THz=1012Hz) called Terahertz waves, sub-millimeter wave and T-Ray refers to the electromagnetic radiation with the frequency range of 0.1 THz to 10THz.The corresponding wavelength range from 3mm to 30μm, and the corresponding energy range is between 0.04kJ/mol and 4kJ/mol.Due to the lack of effective methods of generating and detecting THz radiation, terahertz frequency electromagnetic spectrum is a "gap" to be developed for a long time. In resent years, with the development of terahertz detection and application, terahertz technology has been in an unprecedented process.Terahertz technology is inseparable from the development of terahertz sources, for the reason that THz source is the core technology in THz research. Studies have shown that gyrotron has the maximum output power in terahertz frequency, which based on electron cyclotron principle of stimulated emission. For one hand, the high-frequency interaction structure, in principle, is not indispensable in order to achieve electron cyclotron stimulated emission, while it is very important in designing high-frequency interaction structure for gyrotron working in terahertz band and got attentions from most developed countries for the reason both it will greatly enhance the instability of stimulated emission of electron cyclotron and it helps extracting energy effectively. For another hand, it’s dispensable to study electron-optical systems in order to produce specific electron beams due to the reason that the power output by THz gyrotron is obtained from the excitation source of electron beams, furthermore, it’s important to study electron-optical system that can produce the required electron beams. So, the electron-optical system got attentions from most developed countries as a key part in gyrotron system. Considering the importance of THz technology in the national economy, technology and the modernization of national defense, china’s government has increased investment in terahertz technology research; this paper was completed by the relevant national research funding.The main research and achievements of this thesis are as follows: 1. The dissertation introduced linear and non-linear theory of gyrotron, and electronic optical fundamental theory, with the research on electronic optical fundamental theory from numerical calculation. This helps to understand parameters related in the design.2. By using the calculation program of gyrotron and particle-in-cell simulation software MAGIC, a 3rd-harmonic 0.6THz gyrotron and its required electronic optical system are designed. The magnetic field is simulated by using MATLAB. In the design of 3rd-harmonic 0.6THz gyrotron, the problems of mode competition caused by using high-order harmonic, the power relation among magnetic field, voltage and beam wave interaction, are discussed in detail. In the design of 0.6THz 3rd-harmonic large orbit gyrotron electron beam cusp gun, the influence of the geometric structure of cathode area, the radius of emission area, current density and the size and position of cusp magnetic field on the performance of electron gun are discussed. Lastly, By using the calculation program of gyrotron and particle-in-cell simulation software MAGIC, much simulation and calculation is done which helps to select parameters more reasonably for the aim of optimization by analyzing the results.In the research, we concluded as follows:1. Using high-order harmonic mode can lower the working magnetic field, but the mode competition is serious. Using starting current formula, the relation charts of starting current with the changing of magnetic field and voltage in every mode can be calculated and derived, which is able to restrain the mode competition.2. From the charts of relation among magnetic field, voltage and beam wave interaction, selecting appropriate value of magnetic field and voltage in appropriate range can increase the efficiency of beam wave interaction.3. In the discussion of the influence of the geometric structure of cathode area, the radius of emission area, current density and the size and position of cusp magnetic field on the performance of electron gun, the size and position of cusp magnetic field have the largest influence on the performance of electron gun. Therefore in the design of large orbit electron gun, the size and position of cusp magnetic field is the key factor.