Study of an 8mm Second Harmonic Three-cavity Gyroklystron Amplifier
|School||Institute of Electronics|
|Keywords||Gyroklystron amplifier Second harmonic PIC simulation Theory of small signal Section of coupling ouput|
Gyroklystron amplifier is a novel high-power millimeter-wave coherent radiation source. As a result of high-power capability and high-efficiency and moderate bandwidth advantages, gyroklystron amplifiers have received a great deal of attention in recent years for a variety of applications including high-power radars, electronic counter systems and the next linear collider etc. The magnetic field requirement of the sth harmonic gyroklystrons over cyclotron resonance masers (CRMs) would be reduced by a factor of .s relative to operate on the fundamental cyclotron frequency, so that the amplifier could be applied to highly mobile millimeterwave radar systems. Study of an 8mm second-harmonic gyroklystron amplifier is finished in this dissertation, which especially included in deep theoretical study and numerical simulation of its beam-wave interaction.First, the systematic analysis of the physical mechanism of beam-wave interactions for the harmonic gyroklystrons is finished. By extending the small signal theory to the harmonic gyroklystrons based on the model of the gyroklystron equivalent circuit, the formulas of calculating the small signal gain and the electronic admittance of the resonance cavity of a harmonic gyroklystron are derived. The basic design parameters of an 8mm second harmonic three-cavity gyroklystron amplifier are determined by combining the small signal analysis with such mode choice consideration as sizes of the drift tube, wall losses and space-charge effects etc. The start-oscillating condition in a cavity is studied and the characteristics of bandwidth are basically analyzed from the linear theory of a harmonic gyroklystron, also. These results provide an explain and reference theoretically for the design of the beam-wave interaction circuit of an 8mm second harmonic three-cavity gyroklystron amplifier.Second, the simulation calculation of the high frequency systems of an 8mm second harmonic three-cavity gyroklystron amplifier is finished with R.F structure simulation code HFSS. Not only are the basic operation parameters to the input cavity, bunching cavity and the output cavity determined respectively, but also theoptimized design of the output cavity structure is finished. After the detailed calculations of beam-wave interactions of an 8mm second harmonic three-cavity gyroklystron amplifier with PIC simulation are finished, the visual output pictures and results of the interactions between electromagnetic wave and particles are attained. Based on PIC simulations, the effect of some factors on the output characteristics of the harmonic gyroklystron are studied in which involved in the effect of beam parameters on the efficiency, input power on the gain and the changes of the operating magnetic field on the balance relationship between the output power and bandwidth of the amplifier. These results of calculations are close to that of IAP second harmonic gyroklystron amplifier reported. In addition, relatively ideal results of beam-wave interactions of an actual design structure of the 8mm second harmonic three-cavity gyroklystron amplifier are attained by PIC simulations, which will be a referenced basis as the farther optimized design and actual manufacture-tube in this paper. The detailed analysis of the methods to prevent spurious oscillations in an amplifier for some actual applications is finished by combining PIC simulations consideration. These methods to achieve the operating stability of the gyroklystron amplifiers are very important in actual applications.At last, it is detailedly analyzed to mode coupling characteristics in taper waveguides from the coupled mode theory. Considering weak coupling of modes, the judgement conditions of the main spurious mode excited by the wanted transmission mode in a circular waveguide taper and the destructive conditions of the spurious interference in a finite length of taper waveguide are studied. The reduced formulas for describing the amplitude of the main spurious mode and the formulas of the profile curves of describing taper waveguide are given.