Study On The Stability Of Higher-order-mode Gyrotron TWTs

Millimeter-wave technology has very important applications in high-energy electromagnetic weapon,space detection,radar tracking,high-speed communication,electronic countermeasures and weather forecasting.Gyro-TWT is a kind of electrical vacuum device based on the mechanism of electronic cyclotron maser.It has become a research hotspot because it can obtain broadband,high-efficiency and high-power output signals in millimeter-wave or even terahertz frequencies.With the increase of the operating frequency,in order to improve the capacity and reduce the process requirements,modern advanced Gyro-TWT mostly adopts higher-order mode?HOM?.However,the HOM will lead to more mode competition and more instability factors.The stability factor is the key to the normal operation of Gyro-TWT.Increasing the mode interval is an important means to keep the Gyro-TWT working stably.So the high frequency circuits with mode selection characteristics stand out.In this paper,the dispersion characteristic equation and dispersion curve of multipole profile-shaped waveguide,periodic photonic crystal waveguide and open confocal waveguide are analyzed,and the interval between modes of the dispersion curve of multipole profile-shaped waveguide is compared with that of traditional circular waveguide.Meanwhile,PIC simulation is carried out for the established high frequency structure of multipole irregular-shaped TWT.After optimization of various parameters,the gain of 56 d B and the output power of 180 k W are finally generated.Through the detailed analysis of the mode characteristics of the closed multipole shaped waveguide,periodic photonic crystal waveguide and open confocal waveguide,it is found that the multipole shaped waveguide structure can greatly increase the mode spacing,increase the starting current and length of the low-order mode,inhibit the self-excited oscillation of the low-order mode,and make the tube work stably.The main work of this paper are as follows:Firstly,the dispersion equation of multipole irregular waveguides is studied theoretically.It is found that multipole irregular waveguides can increase the mode interval.Through theoretical research,a series of reasonable parameter values are given,which to some extent avoid the energy exchange between electronic injection and multiple modes,and realizes the effective suppression of parasitic mode.Finally,PIC simulation verification example is given.Secondly,the theoretical derivation of the photonic crystal dispersion equation is summarized.The photonic crystal structure composed of triangular lattice is simulated and analyzed,and the operating mode and dispersion curve of adjacent parasitic mode in the high-frequency structure of W-band photonic crystal are obtained,which proves that the photonic crystal can realize competition mode suppression in the broadband.Thirdly,the dispersion equation of confocal waveguide derived from quasi-optical theory is presented and the theoretical results of HE_0n mode are verified by simulation.Fourthly,at the same time,the analysis of the mode spacing in various waveguides around 90 GHz and the traditional circular waveguide shows that the mode spacing can be effectively increased by multipole shaped waveguide,which makes the interaction more stable.