Research on Magnetron Injection Gun with Curved Cathode for Megawatt-class Gyrotron Traveling Wave Tube
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摘要: 为了满足研制兆瓦级大功率回旋行波管对高压、大电流、低电子注速度零散磁控注入电子枪的迫切需求，本文针对性地给出了一支新型磁控注入单阳极电子枪的设计方案。该新型电子枪方案引入曲面阴极结构，以降低电子枪的速度零散，同时有效增大阴极发射带面积，降低阴极发射密度，从根本上提高电子枪的工作稳定性与寿命。PIC仿真的结果表明：在115 kV、43 A的工作条件下，该电子枪的横纵速度比为1.05，速度零散为1.63%，引导中心半径为3.41 mm，满足应用需求。Abstract:
Background Gyrotron traveling wave tube (Gyro-TWT) is a vacuum electronic device with broad application prospects. Magnetron injection gun (MIG) is one of the core components of gyro-TWT, and its performance directly determines the success or failure of gyro-TWT. From the current research results on MIGs at home and abroad, it can be seen that the working voltage and current of existing MIGs are mostly low, and the velocity spread is generally high, which cannot meet the requirements of future megawatt-class gyro-TWT for MIG.Purpose In order to meet the requirement for MIG with high voltage, high current, and low electron beam velocity spread in the development of megawatt-class high-power gyro-TWT, this paper presents a novel design scheme for a single anode electron gun.Methods The novel electron gun scheme introduces a curved cathode structure to reduce the velocity spread of the electron beam, while effectively increasing the cathode emission band area and reducing the cathode emission density.Results The results of PIC simulation show that under the working conditions of 115 kV and 43 A, the designed electron gun has a transverse to longitudinal velocity ratio of 1.05, a velocity spread of 1.63%, and a guiding center radius of 3.41 mm. The thermal analysis results indicate that the MIG can heat the cathode to1050 ℃ at a power of 76 W.Conclusions The simulation and thermal analysis results indicate that the designed MIG meets the design expectations and satisfies the requirements of high voltage, high current, and low electron beam velocity spread for megawatt level gyro-TWT.-
Key words:
- gyro-TWT /
- MIG /
- high power millimeter wave /
- curved cathode /
- velocity spread
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图 1 单阳极电子枪结构方案和枪区工作磁场分布
Figure 1. Single anode electron gun structure scheme and magnetic field distribution in the gun area
图 2 优化后的电子枪阴阳极间电场以及曲面阴极结构
Figure 2. Optimized electric field between anode and cathode of electron gun and curved cathode structure
图 3 优化前后电子注参数对比以及优化后枪口处电子注切面
Figure 3. Comparison of electronic beam parameters before and after optimization, and electronic beam cross-section at the muzzle after optimization
图 4 工作参量偏差对电子注性能的影响
Figure 4. The influence of working parameter deviation on electron beam performance
图 6 发射带前端以及发射带后端的开缝处理
Figure 6. Opening treatment of the front end and rear end of the emission belt
图 5 电子枪阴极内部初始结构以及热量分布情况和热量流动情况
Figure 5. Initial structure inside the cathode of the electron gun, heat distribution, and heat flow
图 7 电子枪优化后的阴极内部结构以及热量分布情况和热量流动情况
Figure 7. Optimized structure inside the cathode of the electron gun, heat distribution, and heat flow
图 8 电子枪阴极热形变对电子注性能的影响
Figure 8. The effect of cathode thermal deformation of electron gun on electron beam performance
图 9 装配时可能出现的阴极倾斜误差和轴向偏移误差
Figure 9. Potential cathode tilt error and axial offset error during assembly
图 11 高压大电流低速度零散磁控注入电子枪阴极实物加工图和红外测温仪图片
Figure 11. Physical processing diagram of high voltage, high current, low velocity spread magnetron injection electron gun cathode and infrared thermometer
表 1 高压大电流低速度零散电子枪设计输入参数
Table 1. Design input parameters of high voltage, high current, low velocity spread electron gun
Va/kV I0/A B0/T α Δβ rg0/mm P/W Ec/V/m Jc/(A·cm−2) 115 43 1.09 1.05 ＜2% 3.4±1.5 ＜100 ＜1.6×107 ＜10 
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表 2 高压大电流低速度零散电子枪初始设计输出参数
Table 2. Initial design output parameters of high voltage, high current, low velocity spread electron gun
rc/mm ls/mm ϕc fm dac/mm 9.3 7.7 55° 7 12.5
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表 3 回旋行波管电子枪阴极各组件材料
Table 3. Materials of each component of the cathode of the gyro-TWT electron gun
cathode structure material thermal conductivity/
(W·m−1·K−1)thermal expansion
coefficient/(μm·K−1)Young’s modulus/
GPaPoisson’s
ratioemission belt Ba-W alloy 200 4 300 0.28 pre and post formed poles, support and heat shield Mo 138 5.35 330 0.38 filament filling material alumina powder 7 5.5 350 0.22 base steel stainless 50 11 200 0.26
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表 4 阴极各组件形变量
Table 4. Variable deformation of cathode components
cathode component maximum axial deformation/mm maximum radial deformation/mm emission belt 0.343 0.062 pre formed pole 0.335 0.028 post formed pole 0.34 0.06
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