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Overall design and cold test of a G-band gyrotron traveling-wave tube (gyro-TWT) amplifier are presented. This gyro-TWT aims at achieving a goal of 10-kW pulse output power in the range of 210–220 GHz. It is operated in a circular TE01 mode at the fundamental cyclotron harmonics, which is driven by a 50-kV, 3-A gyrating electron beam. Low velocity spread diode-type magnetron injection gun (MIG), multichannel TE01 mode input coupler, broadband metasurface output window, and lossy material loaded beam–wave interaction circuit are simulated and partially measured. Particle-in-cell (PIC) simulation shows that the designed gyro-TWT can achieve a saturated output power over 10 kW in the range of 210–228 GHz with a beam velocity spread of 2.29%. [ABSTRACT FROM AUTHOR]

A diode magnetron injection gun (MIG) has been designed and analyzed for G-band gyro-traveling wave tube (Gyro-TWT). A novel curved surface emitter is proposed to enhance the beam quality. An electron beam with velocity ratio of 1.20 and transverse velocity spread of 2.11% is obtained. The beam transportation stability with geometry misalignment is also analyzed, and the assembly accuracy should be controlled under 0.1 mm. The stray electron is intercepted by the capture structure to avoid the bombardment to the interaction circuit. Then the cathode is fabricated, and the temperature distribution is measured. The experimental result matches well with the simulation. The electron beam quality considering expansion, surface roughness, and thermal emission is estimated, and the total transverse velocity spread is about 2.63%. [ABSTRACT FROM AUTHOR]

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%. Index Terms--35-GHz gyrotron, complex cavity, diode magnetron injection gun (MIG), permanent magnet system, theoretical and experimental study, third-harmonic.

In order to enhance the power capacity of gyro-traveling wave tube (Gyro-TWT), a novel multisectorial-tunnel circuit is presented in this article. The multisectorial tunnel could extend the transverse dimension of RF circuit for higher power electron beam transportation. The azimuthal drifting and transportation distortion performance for rotated electron beam are analyzed. A multibeam magnetron injection gun (MIG) is designed. The electron beam with pitch factor of 1.09 and axial velocity spread of 3.5% is obtained. And the designed cathode was fabricated and temperature distribution was measured. It provides a possible method to enhance the power capacity of Gyro-TWT. [ABSTRACT FROM AUTHOR]

This paper presents the development of highly efficient gyrotron traveling-wave tube (gyro-TWT) with a nonuniform dielectric-loaded interaction circuit. The high-quality electron beam has been generated by curved-profile magnetron injection gun (MIG). With regard to the profile optimization, simulated annealing algorithm (SAA) and genetic algorithm (GA) are applied. An electron beam with a pitch factor of 1.6 and low-axial velocity spread of 0.9182% have been obtained. The parametric sensitivity is discussed in detail. A nonuniform dielectric-loaded circuit has been employed to suppress both global oscillations and local oscillations. Different thicknesses of dielectric materials have been manufactured and measured, demonstrating the circuit loss of oscillation modes that are enough for stable operation. The interaction circuit is analyzed under the guidance of nonlinear self-consistent theory and particle-in-cell (PIC) codes. The tube achieves a saturated peak output power of 36.24 kW at 93 GHz, corresponding to a saturated gain of 54 dB and a maximum efficiency of 45.3% within a 3-dB saturated bandwidth of 5 GHz. [ABSTRACT FROM AUTHOR]

A high-power Ku-band TE01 mode gyro-traveling wave tube (gyro-TWT) with a loss loading structure is designed, fabricated, and tested. A high beam quality magnetron injection gun generating 68-kV, 20–30-A electron beam is optimized to provide a high power radiation. A novel lossy ceramic loaded structure with mode selective attenuation ability is proposed to suppress the potential backward wave oscillation. The interaction circuit is analyzed by linear, nonlinear self-consistent theory, and experiment. An improved wideband input structure design is proposed accordingly. In the hot test, the proposed gyro-TWT produces a 420-kW maximum peak power, about 35-dB saturated gain, 23% efficiency, and more than 1.6 GHz (10%)−1-dB bandwidth in a stable operating condition. [ABSTRACT FROM PUBLISHER]

In this paper, a novel triode-type magnetron injection gun (MIG) with three emitters designed for gyrotron traveling wave amplifiers has been presented. This MIG can be operated in Ku/Ka/Q single band or Ku-Ka/Ka-Q dual band. The optimization of the MIG is accomplished by a multiobjective genetic algorithm method. It is anticipated that this MIG possesses an axial velocity spread of <5% in all the operating frequency bands. The results of sensitivity study show that this MIG can work stably within reasonable parametric windows. Velocity spreads considering cathode surface roughness and initial thermal temperature are analyzed. Cathode configuration with heat insulation chambers is introduced to cut off the thermal flow among the emitters. Thermal analysis has been performed. [ABSTRACT FROM AUTHOR]

In order to enhance the efficiency of confocal gyrotron traveling-wave tubes (gyro-TWTs), this paper is intended to present a novel triode-type magnetron injection gun for a 140-GHz 2-kW confocal gyro-TWT. This novel gun, which has a pair of sectorial emitters, is expected to obtain an axial velocity spread of 7.83% and a velocity ratio of 1.01 with an anode voltage of 35 kV and a beam current of 2.4 A. The design procedure has been given in detail. Computer simulations have been carried out using 3-D electromagnetic code computer simulation technology particle tracing. The sensitivity analysis has been performed to study the parametric dependence of modulating anode voltage, accelerating anode voltage, and cathode magnetic field on beam qualities. Results show that this novel gun can be operated stably within a certain parametric scope. [ABSTRACT FROM AUTHOR]

This paper is intended to present the optimal design of a triode type magnetron injection gun (MIG) for a 300 kW, 30 A gyrotron traveling wave tube (gyro-TWT), which is operated at Q band fundamental TE 01 mode. Based on the analysis of velocity ratio (VR) distribution along the emission strip (ES), a further optimization of cathode geometry on the basis of a preliminary optimized gun is performed, and a new cathode structure is proposed. Compared with initial optimal parameters, the new structure demonstrates a decline of transverse velocity spread (TVS) from 3.66% to 0.57% and longitudinal velocity spread (LVS) from 4.11% to 0.72%, while VR is maintained at 1.05. The achieved overall LVS reaches as low as 3.44% when considering cathode surface roughness and thermal temperature effect. The sensitivity study has been carried out by changing the gun parameters like anode voltage, beam current, and cathode magnetic field to ensure the practical operation stability. [ABSTRACT FROM AUTHOR]

The magnetron injection gun (MIG) is an important component in the gyro-traveling wave tube (gyro-TWT). The electron velocity spread induced to the mismatch of the electric and magnetic fields influences the performance of gyro-TWT. To improve electron beam quality, we designed a modulating anode with curved geometry. And the multi-objective genetic algorithm was employed to optimize the curved geometry. An electron beam with a velocity ratio of 1.05 and low transverse velocity spread of 0.31% in a MIG for a Q-band gyro-TWT is obtained. Compared with the previous design with a transverse velocity spread of 1.17%, the electron beam performance got improved. And the thermal analysis and parametric sensitivity were done. The curved MIG can stably provide an electron beam with a transverse spread lower than 0.8%. [ABSTRACT FROM AUTHOR]

The magnetron injection gun (MIG) is an important component in a gyro-travelling wave tube. To improve the efficiency of the MIG design process, a design tool based on ANSYS Workbench combining with other commercially available software, has been developed. The design process for a Q-band triode MIG is described. A pitch factor of 1.004 and low axial velocity spread of 1.54% were achieved. The results of design tool were validated by EGUN and by numerical calculation. [ABSTRACT FROM AUTHOR]

In our gyro-TWT experiments, low-frequency oscillations (LFOs) had been observed. LFOs is a physical phenomenon usually caused by the electrons trapped between the magnetron injection guns (MIGs) and the interaction region. In this paper, the formation procedure and physical mechanism of LFOs are reported. Available methods including optimizing the magnetic field distribution in the beam compression region and loading bevel cuts on the second anode are involved to capture the trapped electrons, suppress the LFOs and improve the helical electron beam quality. Simulations and experimental results are in good agreement with each other and also reveal the reasonableness of this means. Finally, the influence of current capture ratio on LFOs and the beam quality are studied. With the current capture ratio increasing, the amplitude of LFOs decreases, the pitch factor maintains a constant about 1.2 and we also demonstrate a low transverse velocity spread about 3%. [ABSTRACT FROM AUTHOR]