Gyrotron Key Technologies

Although this is a era of solid state semiconductor devices,microwave tubes are still extensively employed in certain areas for applications where their solid state counterparts are not able to compete as far as delivering the required high power and high frequency.Gyrotrons as an important power of microwave to milli-metric wavelengths,are applied in ECRH,radar,and commercial sintered,and so on.Because their broad applications for military and civil,they are took seriously by many countries.This paper is organized as follow three parts:First,high-frequency,high-power gyrotron oscillators are under development for plasma heating in future fusion reactors.The main technological constraint in the design of a gyrotron cavity is the thermal wall loading,which must be limited to 2-3kW/cm² for long or CW operation.To reduce the wall loading it is necessary to increase the cavity diameter,and thus high-frequency operation requires the use of high-order modes, beam positioning doesn't provide a sufficient means for mode selection and stability, and mode competition becomes a serious physical constraint.So,the coaxial cavities with corrugated inner conductor was chosen to solve above problem.This paper based on the kinetics of electron cyclotron maser,associated with the linear theory of gyrotrons and homogeneous impedance surface method,we study the high frequency structure of coaxial cavities with corrugated inner conductor for high power gyrotrons and its characters of mode selective and depressing thermal wall loading.Build a three dimension PIC(particle in cell) model for 170GHz coaxial gyrotron. We got a stable MW power output of single mode.Second,the study of high-power mode converters continues to be of great interest for a number of microwave applications,because the desired mode for the applications is usually different from the output mode of source,and the converters are needed to make the transformation.Based on the coupled wave theory,this paper presents the design,numerical analysis,and simulation of two types TE_0n-TE_0(n+1) ripple-wall waveguide mode converter:a uniform ripple-wall converter and a nonuniform ripple-wall waveguide converter.For the first type,17.17GHz,six periods,TE₀₂-TE₀₃ mode converter and 34.30GHz,six periods,TE₀₁-TE₀₂ mode converter were operated;and 34.30GHz,six periods,TE₀₁-TE₀₂ for the nonuniform one.The emphasis of the design study is to maximize the convert efficiency and mode purity with a broad bandwidth.The nonuniform ripple seems to have a significant advantage over the constant ripple design for the mode converter,convert efficiency reach 99.5%at center frequency and get a convert bandwidth more than 1.5GHz.Study a helical waveguide(serpentine-type) TE_m1-TE₁₁ mode converter.Design, numerical analysis,and simulate a 94GHz,six periods,TE₀₁-TE₁₁ mode converter and analysis,simulate a 10.24GHz,four periods,TE₃₁-TE₁₁ mode converter.The emphasis of the design study is to maximize the convert efficiency and mode purity with a suitable bandwidth.The convert efficiency of these two devices reach 98%at center frequency and get a good convert bandwidth.Simulation of these two kinds mode converters agree well with the theoretical results.Third,as the key part of gyrotrons,the beam characteristics affect interaction output power and efficiency directly.Combining with the prospect of our laboratory, design the MIG and large-orbit electron gun.Study shows finishing initial design of gun we can optimize the beam performance by adjusting magnetic field distribution,gun geometry,cathode magnetic field,magnetic field compression ratio,anode voltage, cathode emitter temperature and so forth.Especially,analyze qualitatively the effect that the cathode magnetic field angle contributes to beam ratio and prove it by calculation.Especially for the transverse signal input mode of cyclotron amplifier,this paper originally pose a method which the signal input from the cathode coaxial waveguide. The simulation agree well with the theoretical results both in terms of electronic beam parameters and quality of input signal.