Research On S-band Low Magnetic Field Relativistic Backward Wave Tube Oscillator

The relativistic backward wave oscillator(RBWO)is one of the most promising high power microwave(HPM)devices due to its high power and high efficiency.However,the ordinary RBWO operating at high guiding magnetic field requires an magnet with large volume,which limits the application of RBWO.In order to reduce the guiding magnetic field intensity required by the device,theoretical analysis,particle in cell(PIC)simulation and experimental research on an S-band low magnetic field RBWO are carried out,and the miniaturized magnet of the RBWO is designed.Firstly,the cyclotron resonance absorption effect of the RBWO is analyzed,and the guiding magnetic field intensity of electron cyclotron resonance absorption is derived from the cyclotron resonance synchronization condition.Then,based on the equations satisfied by the electron distribution function and its perturbation term in the device,the variation of the output power with the intensity of the guiding magnetic field in the RBWO is derived.At the guiding magnetic field of electron cyclotron resonance absorption,the output power drops significantly to zero.The operating area of the RBWO is divided into a low magnetic field region and a high magnetic field region by the cyclotron resonant magnetic field.Secondly,the PIC simulation of S-band RBWO under low magnetic field conditions is carried out.By increasing the distance between the electron beam and the inner wall of the RBWO,the transmission efficiency of the electron beam can be enhanced.Moreover,a special slow wave structure is designed to improve the efficiency of beam-wave interaction under low magnetic field.The slow-wave structure is divided into two sections.The length of the front-stage period is large and the corrugation depth is shallow,which ensures that the structural wave phase velocity of the slow wave structure is synchronized with the electron velocity to realize the modulation of the electron beam.The latter-stage slow-wave structure has a short period length and a deep corrugation depth,which reduces the structural wave phase velocity of the slow-wave structure and improves the beam-wave interaction impedance,even though the electron beam is relatively far away from the surface of the slow-wave structure.The structural parameters of RBWO and the guiding magnetic field intensity are optimized by particle simulation.The PIC simulation shows that a microwave with a power of 770 MW,an efficiency of 23%and a frequency of 2.84 GHz is obtained when the guiding magnetic field is only 0.17 T.The S-band low magnetic field RBWO experimental study is then carried out on the long pulse accelerator.Under the conditions of the guiding magnetic field of 0.17 T,the beam voltage of 510 kV,and the current of 6.9 kA,a single pulse microwave with a pulse width of 47 ns,a power of 722 MW and an efficiency of 20%is obtained.Experiments are carried out at a repetition rate of 10 Hz under the same guiding magnetic field conditions,and a 10 Hz repetitive microwave with an average power of 679 MW is obtained.Finally,the miniaturization of the matching magnetic field is carried out for the S-band low guiding magnetic field RBWO.Compared with the magnet required by the ordinary S-band RBWO,the outer radius of the matching solenoid magnetic field is reduced by 20%,and the energy consumption is reduced by 92.1%.