The Design Of S-band Four-cavity Relativistic Klystron

In the field of high-power microwaves, devices’ output power are limited. On the contemporary, technology and research demands for higher microwave power, so scientists proposed a power combining[1] technology. Effected by this technology, klystron has been widely concerned. Nowadays relativistic klystron commonly uses three-cavity structure, this simple structure not only easier to adjust but also easier to suppress oscillation; however the gain is limited(~30 dB). To improve the gain of klystron, we try to design four-cavity relativistic klystron, however this kind of structure faces technical problems of mode control. Aiming at this problem, the dissertation carried out study about theoretical analysis、particle simulation and experiment. And have analyzed self-excited oscillation’s effects on stability of output microwave, such as electronic returning、high-order mode oscillation.First, the dissertation have analyzed klystron’s basic working principle and described the process of beam-cavity interaction. Established the equivalent circuit model for the different functions of cavities(such as: input cavity、idle cavity and output cavity). This kind of circuit model makes the beam-cavity interaction easier to understand.Secondly, the dissertation has finished design of four-cavity intense relativistic klystron through particle simulation. Against how to choose right electron beam parameters(such as beam voltage, beam current and size) and guiding magnetic field, this paper has made a detailed analysis according to the given indicators. And for the effect factors of output microwave’s stability, this dissertation has carried out a research. Analyzed the causes of electronic reflection and high-mode oscillation from theory, searched the suppression measures, and have validated through simulation. To achieve both suppression of self-excited oscillation and high microwave power, a ladder structured drift was adopted. At last, achieved a stable microwave[1] with the power of 3.74 GW, efficiency of 22%, 1 dB bandwidth of 74 MHz through simulation.Finally, this dissertation have carried out the experimental study on four-cavity relativistic klystron on the use of summarized measures in simulation, and have the self-excited oscillation effectively suppressed. In the excitation of kW level injection microwave, we have achieved a gain of 61 dB, efficiency of 24%, pulse width of 80 ns.