Numerical Simulation Study On Three Dimensional C-band Multibeam Klystron

Based on the single beam klystron, multi-beam klystron(MBK) is a kind of microwave power amplifier parts. With low voltage, broad bandwidth, high efficiency and high gain, MBK has been widely used in the areas of scientific research, defense and economy. As one of the indispensable step of design a high power vacuum microwave source device, simulation plays an important role.This paper mainly studies on the theoretical analysis and numerical simulation of the C-band MBK with the full three-dimensional method. At first, adopting the theory of space charge wave and high current electron beam optics in high power klystron, this paper analyze the interaction process between the electron beam and the electromagnetic wave of the single beam klystron. Then, on the basis of the single beam klystron research, the theory of the MBK beam-wave interaction has be analyzed and calculated.Secondly, using the CST software, the high frequency structure of the MBK has been studied. In the research,it focus on rectangular reentrant cavity for its high coupling impedance. Considering the structural parameters of the rectangular reentrant cavity, the middle cluster cavity, the in- and out- put cavity, and the resonator parameters of the cavity, I finally determined the operating parameters, such as the working mode, the resonant frequency, characteristic parameters and so on. In particular, in the progress of calculation the external quality factor of the input and the output cavity, the impact on the appearance of the size of the coupling mouth quality factor has been emphatically studied.Thirdly, the CHIPIC software has been used to analyze and simulate the electron optical system of the MBK. When simulated the electron gun, it takes one beam on the spindle to simplify the calculations. According the results of the calculation, the electron beam parameters and the magnetic field distribution of the electron gun area has been defined The magnetic focus mode, size and distribution has been adjusted to improve the electron beam radius、laminarity and electronic pass rate. Because the mulit- beam shares a collector, so in the collector entrance, it easily forms a virtual cathode, causing the reflection of electrons, and deteriorating the stability of the whole device. So optimizing the collector structure and the collector region magnetic field is important. Finally, get the result that the electron is divergent and have no electronic backflow. After determining the basic parameters of the electron optical system configuration of the klystron, the electro-optical system has been modeled and calculated.Finally, the three-dimensional model of MBK has been simulated by CHPIC software. The relationship between the electrical parameters and the output power is analyzed at the beginning of this part. Then the relationship between the dimension of coupling hole and the stability of output power has been analyzed carefully. At the end of this paper, under the conditions that the electron beam voltage was 28 kV, the total current is 43 A, the input frequency is 5.6GHz, the input power is 50 W, The MBK gets 760 kW peak output power,380 kW average power, and the efficiency is 57%, the gain is 40 dB approximately, the bandwidth is 200 MHz.