Theory And Simulation Research Of A 250 GHz Gyrotron

Terahertz（THz）waves locate between far infrared and millimeter wavelengths,have great potential inapplication.Gyrotron oscillator is one kind of promising THz sources with high power and high efficiency.To satisfy the requirement of THz sources with power of hundreds watts in military,biomedicine and other fields,this dissertation uses linear theory,single-mode self-consistent nonlinear theory and the software Vsim which can run parallel with 64 CPU cores to investigate the theory and simulation of a250 GHz Gyrotron.The particle simulation results show that single-mode of TE_5,2 with power of 331 W could be achieved at beam voltage of 10 kV and beam current of 100mA.The detailed contents of this dissertation are as follows:1.The results of linear theory show that the operating mode is TE_5,2,the cavity radius is almost 2 mm and the guiding center radius is about 1mm.The resonant frequency is 248.6 GHz and the Q factor is 11320 at the parameters of initial interaction cavity.The main competition modes are TE_0,3 and TE_2,3 modes which are both at backward wave oscillation region.The main influence factors of start oscillation currents is external magnetic field.The effective working regions of external magnetic field and beam voltage are 9.00-9.05 T and 8-13 kV operating at TE_5,2,2 mode.2.The single mode self-consistent nonlinear analysis based on linear theory indicates that the proper cavity radius could be 2.01 mm or 2.02 mmand the middle cavity length is 19 mm.The varation of input and ouput transitions sections have little effect on beam-wave interaction effiency.The beam-wave interaction effiency is maximum at 9.00 T-9.02 T of external magnetic field,9 kV-11 kV of beam voltage,and pitch factor of about 1.4.At the beam current of 100mA and the guiding center radius of1.0mm,the final optimized effiency is 36.8%and the hot cavity is 249.2 GHz.The self-consistent nonlinear theory anylsis presents optimized parameters for paticle simulation.3.The particle-in-cell（PIC）simulation results of Vsim,which can run parallel with64 CPU cores,are almost consistent with the results of Magic.Vsim demonstrate significant superiority of computing speed.The TE_0,3 mode at backward wave oscillation region leads to mode competition.The suppression of backward wave oscillation is achieved through adjusting the dispersion curves.Finally,the PIC simulation results of the gyrotron operatign at TE_5,2,2 mode is frequency of 249.3 GHz and effiency of 33.1%,which is almost consistent with the results obtained through the nonlinear theory anlysis.