Parameters to Define the Electron Beam Trajectory of a Double-Tapered Disc-Loaded Wideband Gyro-TWT in Profiled Magnetic Field

In the method of tapering the cross section of the interaction structure for broadbanding a gyro-TWT, the different portions of the interaction length of the tapered-cross-section waveguide become effective for different frequency ranges if the magnetic field and beam parameters are profiled to maintain the condition of electron cyclotron resonance throughout the interaction length. In the present paper, the study of profiling the magnetic field and beam parameters in steps of the stepped analytical model of a double-tapered disc-loaded circular waveguide was made throughout the steps of the model. In the observed profile, the magnetic flux density in a typical step relative to its value in first-step decreases from first-step (gun-end) to end-step (collector-end) of the model considering the up-tapering schemes, in which structure parameters increase from gun-end to collector-end. Also, the transverse beam velocity in a typical step relative to its value in first-step decreases from gun-end to collector-end. However, the Larmor radius in a typical step relative to its value in first-step as well as the hollow-beam radius in a typical step relative to its value in first-step, both increase from gun-end to collector-end in the model considering the up-tapering schemes.     

Effects of the sever on two-stage gyro-TWT amplifiers

The effects of the sever on two-stage gyro-TWT amplifiers were characterized by a self-consistent slow time scale model. Utilization of a sever was demonstrated to be capable of inducing additional launching losses as well as ballistic bunching effects. In addition, some electrons could bunch on an electron phase equal to 3π/2 at the beginning of the second stage as a result of a large and sharp change of the wave’s phase if the modulation of the electron beam in the first stage was strong. Calculated results further indicated that the performance was more sensitive to the position of sever than the length of the sever. Asymmetric interaction structures with the first stage being shorter than the second stage demonstrated higher saturated powers and wider bandwidths along with exhibiting more resistance to the velocity spread of the electron beam.     

Q波段回旋行波管宽带高平均功率输出窗设计与热分析

利用场匹配理论建立传输级联矩阵的方法对多层窗片结构输出窗进行研究,通过大量的数值计算给出Q波段回旋行波管一种新型中间风冷结构输出窗的参数,然后通过数值计算和HFSS仿真验证,该新型输出窗在46~50GHz范围内,S11反射系数小于-20dB。在此基础上进一步对该输出窗进行热分析,热分析表明:新型输出窗窗片中心与边缘温差与传统输出窗相比大幅下降,热应力大大减小,提高了输出窗的功率容量。回旋行波管工作在TE01模式时,新型输出窗获得的最大饱和功率容量达到90kW,与传统输出窗相比,功率容量提高了21.8kW。     

Beam Characteristics of Mechanically Tunable Magnetron Injection Guns

Gyrotron has received extensive attention owing to its high-power capability, particularly when the wavelength shrinks below the millimeter-wave range. The electron beam of a gyrotron is typically generated by a magnetron injection gun (MIG), and a mechanically tunable MIG is employed to enhance the beam quality. However, a slight adjustment in the position of the center electrode of the mechanically tunable MIG can cause significant modification of the electric-field profile. Consequently, the cathode current of the mechanically tunable MIG is not only dependent on the cathode temperature, but also the relative position of center electrode. To accurately determine the beam characteristics of the mechanically tunable MIG, an improved computer program is employed to simulate electron trajectories. Simulation and measurement results indicate that although the magnetic field and compression ratio do not influence the beam current of the mechanically tunable MIG, but the beam current of the MIG depends on the cathode temperature and relative position of the center electrode. Finally, an improved mechanically tunable MIG design is developed to enhanced an beam quality while minimizing beam current variation.     

Improved Computer Program for Magnetron Injection Gun Design

Gyrotron has received extensive attention owing to its high-power capability, especially when the wavelength shrinks below the millimeter-wave range. The electron beam of a gyrotron is typically generated by a magnetron injection gun (MIG). For high cathode current density, the MIG may operate in a region that combines temperature limited and space-charge limited emissions. An improved computer program for electron gun design is appropriate for MIGs that operate between space-charge limited and temperature limited emission. Moreover, the initial input formation of the program resembles that of the EGUN code. Analysis of a Pierce electron gun and MIGs reveals that the stimulated beam current appears consistent with the measured results. However, EGUN simulation results in which the cathode emitters of MIGs are chosen for the temperature limited emission differ from those of our simulation results. This difference is most likely owing to that the initial emitting energy can not be completely described in the EGUN simulation. Finally, the improved computer program is used to design a MIG for a Ka-band, TE₀₁ mode gyro-TWT.     

螺旋波纹波导回旋行波管注波互作用非线性理论

螺旋波纹波导回旋行波管与采用光滑圆波导的回旋管相比,有较大的带宽。介绍了该类回旋行波管的非线性注波互作用理论。计算结果表明该理论计算结果与实际实验报道的结果基本符合,相应的电子效率达到29%,饱和增益达到37 dB,工作磁场0.21 T,电压185 kV,电流19 A。     

Kα波段介质加载回旋行波管小信号分析与设计

应用分析回旋行波管绝对不稳定性的Briggs-Bers相碰判据与小信号色散方程,并结合介质加载波导的冷场分析,通过数值计算比较了不同介质加载条件下回旋行波管工作模式的起振电流与寄生模式的起振长度,通过改变加载介质的特性参数从而增加行波损耗可以显著提高工作模式起振电流,并抑制掉寄生模式的返波振荡.结合介质加载波导冷场分析与回旋行波管小信号色散方程,分析了介质加载条件下回旋行波管小信号增益,给出了不同介质加载条件下的回旋行波管的小信号增益带宽曲线.在对介质回旋行波管自激振荡与小信号增益的综合分析基础上,对Kα 关键词： Kα波段介质加载回旋行波管 绝对不稳定性 自激振荡 小信号增益     

W波段螺旋波纹波导回旋行波管注波互作用的非线性分析

本文从有源麦克斯韦方程组出发, 系统地推导了螺旋波纹波导的色散方程及非线性注波互作用理论, 数值计算结果与已有的实验报道基本相符.在此基础上,设计了W波段螺旋波纹回旋行波管, 工作电压80 kV, 工作电流5 A, 中心频率95 GHz, 3 dB带宽约4.5%, 饱和增益52 dB, 最大输出功率142 kW, 电子效率达20%-35%.最后,本文计算了电流, 电压及输入功率的改变对W波段螺旋波纹波导回旋行波管输出性能的影响.     

ELECTRON BUNCHING CHARACTERISTICS IN THE GYROTRON TRAVELING-WAVE AMPLIFIER WITH TWO-STAGE INTERACTION CIRCUIT

Based on a simplified model, an analytic theory describing the bunching of the electron beam in a gyrotron traveling wave tube (gyro-TWT) with two-stage interaction circuit is presented. The analytic formulas of the traveling-wave bunching parameter, ballistic bunching parameter, and the density of the bunching beam are obtained. The bunching procedures corresponding to different harmonic operations are studied. It is shown that the maximum of harmonic component depends on the ratio of the harmonic number in the output stage to that in the input stage, not on their absolute values.     

螺旋波纹壁圆柱波导回旋行波放大器的非线性模拟

 给出了螺旋波纹壁圆柱波导回旋行波放大器非线性模拟中,处理偏模的初值问题和计算精度瞬时监测问题两项关键技术。采用这些技术编制的程序所得到的数值计算结果与Denisov等人实验观测值符合得很好。在此基础上,对电子束速度离散、螺旋开槽周期和开槽深度对效率的影响,进行了非线性模拟研究。结果表明：螺旋波纹壁圆柱波导回旋行波放大器效率对电子束速度离散不敏感,而对螺旋波纹开槽周期和开槽深度的依赖性较强;通过参数优化可望把目前实验的效率水平提高到25.6%。