| One of the urgent needs of current high power microwave technology is to turn high power microwave sources into practical and reliable systems.High power microwave sources during operation convert the energy of the electron beam into energy of microwave.In this process,an external magnetic field is often required to guide the stable transmission of the electron beam.Current magnetic guidance system is large in volume,weight,and has high power consumption,so it is becoming increasingly impractical in engineering applications.The periodic permanent-magnet focusing system has the characteristics of light weight and no power consumption.In this context,the paper studies the transmission feasibility of annular intense relativistic electron beam in the periodic permanent magnet focusing system.The research has scientific and practical value.According to the characteristics of the annular intense relativistic electron beam and relativistic klystron amplifier,the coaxial periodic permanent magnet focusing system is provided in this paper.Firstly,the approximate expression of the magnetic field of the coaxial periodic permanent magnet focusing system is derived.Next the single electron theory is applied to derive the radial equilibrium equation of the intense annular electron beam transmission,and the stable propagation condition of the electron beam is obtained.In order to analyze the transmission characteristics of intense electron beams,a model is established and the general patterns of magnetic field parameters affecting electron beam transmission are discussed.Aiming at coaxial relativistic klystron amplifiers,a coaxial periodic permanent magnet focusing system is designed based on theory and analysis,and its application of periodic permanent magnet focusing system is further verified in simulations.The main work of this paper include the following aspects:A suitable magnetic circuit structure is applied in this paper,in which the field type is a periodic cusped field and the magnetic circuit structure is Halbach type.According to the structure and boundary conditions of the magnetic field,the approximate expression of the magnetic field is obtained.The numerical results of the magnetic fields are compared with the simulation results of the magnetic fields to verify the correctness of the magnetic field expression.According to the single-electron motion theory,the radial force equilibrium equation of intense current annular electron beam in a coaxial periodic permanent magnet focusing system is deduced.The characteristics of the equilibrium equations are numerically analyzed and the stable transmission conditions of the electron beam are obtained.In order to analyze the electron beam transmission characteristics in the coaxial drift tube,the space charge confinement flow and the Brillouin magnetic field of the electron beam in the coaxial drift tube are analyzed.The model of electron beam transmission channel is established.And the influences of magnetic field parameters on electron beam transmission are discussed by particle-in-cell software.Aiming at the Ka-band coaxial relativistic klystron amplifier,a coaxial periodic permanent magnet focusing system is designed.The simulation results show that under the conditions of magnetic field period of 18 mm and amplitude of 0.33 T,the coaxial relativistic klystron amplifier with voltage of 500 kV and current of 6 kA obtains an optimal output microwave power.Compared with the results obtained when klystron is focused by uniform magnetic fields,it is found that the power output obtained with the coaxial periodic permanent magnet focusing system is also good.The research results show that it is possible that the periodic permanent magnet focusing system can be applied to coaxial relativistic klystron amplifier,which provides a reference for the compact development of high power microwave sources. |
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