Hongfu Li

A 35-GHz low-voltage third-harmonic gyrotron with a permanent magnet system

A systematic theoretical and experimental study on a 35-GHz 45-kV third-harmonic gyrotron with a permanent magnet system is presented in this paper. A complex cavity with gradual transition and a diode magnetron injection gun (MIG) are employed in the gyrotron. A self-consistent field nonlinear theoretical investigation and numerical simulation for electron beam interaction with RF fields are given. The diode MIG is simulated numerically utilizing our code in detail. The permanent magnet system provided the maximum axial magnetic field of about 4.5 kG in the cavity region of the gyrotron. The Ka band third-harmonic complex cavity gyrotron with a permanent magnet system has been designed, constructed, and tested. A pulse output power of 147.3 kW was obtained at a beam voltage of 45 kV with beam current of 32.2 A, corresponding to an efficiency of 10.2%.

Study of a 35-GHz third-harmonic low-voltage complex cavity gyrotron

A self consistent nonlinear theoretical model for a complex cavity gyrotron with abrupt transitions is presented in this paper. The model accounts for mode conversion in the transition region of the complex cavity through the general theory of modal expansion techniques. The interaction between the electron beam and TE/sub 61//TE/sub 62/ RF field in the step cavity for a third-harmonic gyrotron is simulated; many calculations are carried out under different electron beam parameters.

Numerical Simulation Study of Double-Beam Magnetron-Injection Guns for High-Power Gyrotrons

This paper describes the detailed design of the double-beam coaxial magnetron-injection gun (DBMIG) for use in Ka-band coaxial gyrotron with two beams operating in the harmonic mode. The DBMIG operating voltage is 70 kV with a total beam current of 20 A, evenly divided among the beamlets, and provides two 70-kV 10-A beams with a velocity ratio of 1.5. The minimum of the transverse velocity spread and the axial velocity spread are about 3% and 5%, respectively. The emitter current density has been kept below 10 Amiddotcm-2 (space-charge limited). The primary computational tools used in the design process were the self-consistent particle-in-cell simulation code MAGIC

Study of a high harmonic gyrotron with inner slotted coaxial structure

Abstract The interaction between electron beam and wave field of high harmonic gyrotron with inner slotted coaxial structure is analysed and calculated in this paper. The optimum interaction efficiency is numerically illustrated for the 8th cyclotron harmonic TE81 π-mode atf0 = 35GHz. The influence of electron velocity distribution in cusp-injected system, beam voltage, and length of resonator on the efficiency is taken into consideration in numerical calculation. The results show that the inner slotted coaxial structure is good for an increase in the interaction efficiency.

A new method for the design of a quasi-optical mode converter with a special reflector

This paper presents a new method for the design of a special reflector for quasi-optical mode converters, using the combination of vector diffraction theory and geometrical optics. The reflector is formed in a piecewise manner, according to a base reflector shape chosen previously. Each piece of reflector cell is adjusted separately. A numerical example is carried out for the quasioptical mode conversion of a circular waveguide TE/sub 52/ mode at 35 GHz, and the calculated results show that the output Gaussian wave beam waist radius is only less than twice the wavelength.

Experimental study of an interaction structure with distributed loss for a Ka-band gyro-TWT

The distributed-loss technology has been successively applied in many gyro-TWT experiments to suppress absolute instabilities. Based on the stability analysis of a Ka-band TE01 mode gyro-TWT with a distributed-loss interaction circuit, propagation losses of operation and parasitic modes are calculated and dielectric loss parameters, including thickness of the loss layer and relative permittivity, are decided. Taking advantage of the optimised parameters of a loaded dielectric, a high-gain scheme is demonstrated in a 34 GHz, TE01 mode gyro-TWT, producing 160 kW saturated output power at 40 dB, stable gain and 22.8% efficiency with a 3-dB bandwidth of 5%.

Self-Consistent Nonlinear Theory of Inner-Slotted High Harmonic Gyrotron

The self-consistent nonlinear theory is employed to analyze the inner-slotted high harmonic gyrotron, it is found that the structure of advantiageus to the interactin, the efficiency of interaction is above 30%.

Nonlinear Theory of a Corrugated Coaxial- Gyrotron With Misaligned Inner Rod

The effects of a small misalignment of the inner rod in a corrugated coaxial-gyrotron on eigenvalue, resonant frequency, and electronic efficiency, and so forth, are presented. As a practical application, with the electronic velocity spread and cavity wall resistivity being taken into account, the beam-wave interaction of a 170 GHz megawatt corrugated coaxial-gyrotron operating with TE31,12 mode has been investigated. The results show that the eigenvalue increases slightly when the ratio of misalignment to outer radius D/R increases in the case of small ratio of outer to inner radius C= R/Rin, but is uniform in the case of large ratio of C . The electronic efficiency decrease slightly when D/R increases within the range of 0-0.01. If D/R increases to 0.02, the efficiency decreases seriously to only about 5%. For both cold cavity and hot cavity, the resonator frequency increases with D/R increasing.

Analysis of High Power Millimeter Wave Waveguide Mode Converters with Input Mode Mixture

Based on the coupled mode theory, this paper presents the study on the influence of input mode mixture in circular oversized waveguide mode converters. Three kinds of commonly used waveguide mode converters, including the waveguide mode converters with varying wall radius or small axis perturbations, and the waveguide mode converters with bent structures, are taken as the examples. The results show that the spurious input modes do not simply superimpose onto the output modes, and in some cases they may deteriorate the conversion efficiency for the main output mode. Methods for transforming such spurious input mode mixture simultaneously into the main output mode are also presented in this paper.