Study On The Related Issue Of The Photonic Band Gap Resonator Gyrotron

The terahertz band is sandwiched between the millimeter wave and infrared wave spectrums. It has the characteristic of millimeter wave and light at the same time, has important application prospect. The generation and application of the wave in such frequency range have drawn spectacular attention all around the world. Meanwhile, the gyrotrons have been proven to be one of the most promising devices to deliver high power terahertz signals. To enlarge the size of the beam-wave interaction cavity in the terahertz band where the wavelength is quite short, the devices are usually designed and operated with high-order modes. However, the corresponding competition mode of the high-order mode is more, to solve the problem of serious competition of the high-order mode, the new structure of the beam-wave interaction circuit is necessary to be studied. Because of the photonic band gap properties of the photonic crystal, if we let the work mode locate in the photonic band gap by removing some rods in the lattice, it can reduce the mode density, reduce competition mode. Thus the study of the photonic band gap and the related structure of the gyrotron are demanding.In this paper, based on the lattice theory of solid state physics, the band gap characteristics of photonic crystal were studied, with the introduction of defects, using the band gap characteristics of photonic crystal, a 0.1THz photonic band gap resonator worked in like-TE04 mode was designed. And the optical system and output window of the photonic band gap gyrotron were be analyzed.The main content and contribution of the thesis can be outlined as below:1、From Maxwell’s equations, eigen mode equation of photonic crystal structure have been derived, introduced the characteristics of photonic crystal: Scaling law and band gap properties. According to the lattice theory of solid state physics, obtained the two-dimensional photonic band gap characteristics for the dielectric materials and metal materials photonic structure. Through combined the theory and extensive numerical simulations, obtained the global photonic band gaps for TE modes in square and triangular lattices for the oxygen free copper material rods.2、In order to obtain high mode purity in the cavity, the two-dimensional triangular lattice photonic crystal structure was studied. According to the theory of cut-off frequency in the cavity and the triangular lattice global band gap, a mode map which can be examine the occurrence of the possible modes in the PBG cavity with the relationship between the structure and frequency can be obtained, these figures can be used as the guidance of choosing the dimensions of the lattice and the operation mode. The operating mode was chosen as TE04-like mode as it has less mode competition and is able to get a better interaction with the electron beam. Through the theoretical analysis and software analyzed the mode distribution in the PBG resonator, and the TE04-like field distribution in the PBG resonator is similar in a cylindrical waveguide. Through theoretical analysis determined the working parameters for the 0.1 THz gyrotron, such as operating voltage, current, magnetic field, guiding center radius.3、Analyzed the theory of the magnetron injection gun(MIG) for gyrotron devices, according to the theoretical analysis results, combined to the requirements of the interaction parameters, the initial structure of the electron gun is obtained for the 0.1THz gyrotron. According to a large number of simulations by the electron trajectory PIC code, the MIG has been simulated and optimized. Two electron gun structures are introduced which have been applied in the experiment. One of the structures is the single anode MIG which is designed for the W band gyrotron, the electron guiding center radius of this gun is 3mm, the transverse and longitudinal velocity ratio is 1.4, and the speed spread is less than 3%. The another gun structures is two anode MIG which is applied to 420 GHz second harmonic gyrotron, the electron guiding center radius of this gun is 1.95 mm, the transverse and longitudinal velocity ratio is 1.4. The experimental measured results of these two gyrotron device is well, consistent with the theoretical design, verified that the theory and the particle-in-cell code is accurate.4、Introduced several kinds of commonly used output window, the reflection characteristic of the single layer dielectric window is derived by using the mode matching technique, and this method has been justified by comparing with the commercial software simulation results. Uses this theory method can fast design the waveguide window with high transmission. To get a wide bandwidth and high transmission output window, multi- layer window come up, the simulation of multi- layer window is similar with the single- layer window, the only difference is that more transfer matrices need to be cascaded. In order to better transmission HE11 mode, a new Brewster window structure has been presented by the author, the structure is integrated a Brewster window into a corrugated waveguide. This new Brewster window was numerically optimized and verified by measurement using a Vector Network Analyzer. The reflection of this Brewster window is less than-22 d B over the frequency range of 84-102 GHz.