Study On X-band Relativistic Backward Wave Oscillator With Low Magnetic Field

In research of the relativistic backward wave oscillator(RBWO), we need the magnetic field to constraints and guidance when the electron beam gets through the component, mostly of the relativistic backward wave oscillator’s guiding magnetic field requires more than 3T. Spiral tube pulse magnet usually can only work in the single pulse condition in general, it restricted the RBWO work in the repetition frequency. In order to realize the device repetitive operation, we will need to use superconducting magnets to provide guiding magnetic field or develop the relativistic backward wave oscillator with low magnetic field from the design methods. It is unfavorable to develop the high power microwave source(HPM) system miniaturization because the superconducting magnetic field system has huge volume.So this paper reduced the relativistic backward wave oscillator’s guiding magnetic field from the devices design and studied the relativistic backward wave oscillator’s working conditions with low magnetic field in detail.Firstly, the paper analyze the relativistic backward wave oscillator working magnetic field requirements from the cyclotron resonance theory and do theoretical research on RBWO working at low magnetic field conditions,.We study the reason of why RBWO can work at low magnetic field and do researches on the dispersion characteristics of slow wave structure. The paper also derived the formula which uncovers the relationship between microwave power and magnetic field from the single wave hypothesis and perturbation hypothesis theory.Secondly, based on the parameters of permanent magnet and combined with the advantages of high power microwave devices, an X-band relativistic backward wave oscillator with low magnetic field is designed. We use the magic program to run simulations of RBWO and analyze the influences of the slow wave structure, the diode voltage and beam current on the operating characteristics of the RBWO. Then the paper optimize the parameters of the device, it greatly improve the beam wave conversion efficiency through the device of the non-uniform slow wave structure. It is shown from the particle-in-cell(PIC) simulation that the 1.1GW output microwave power and 30%efficiency is obtained.Finally, this paper uses single pulse magnetic field to demonstrate the RBWO experiment by a pulsed solenoid magnet and provides the necessary experimental data for the permanent magnet RBWO packing. Based on the stable microwave output of experimental data of RBWO, the RBWO is simulated by the magic program in which the field distribution is similar to permanent magnet. Then the RBWO is experimentally investigated by using the permanent magnet to provide a magnetic field, we get the experiment results agree well with the ones obtained by pulsed magnetic field. At last the experiment of RBWO is finished in the repetition frequency of 20 Hz, the results of which show that the RBWO can work steady in repetition frequency of 20 Hz. The experimental results lay a good foundation for the permanent magnet RBWO packing and provide the necessary conditions for the HPM system miniaturization.