摘要
设计了用于G波段行波管的聚焦极调制皮尔斯电子枪,电子注电压20 kV,电流50.9 mA,注腰半径0.056 mm,射程10.3 mm。利用热-结构耦合分析和电子注轨迹仿真方法,分析了热形变对电子枪性能造成的显著影响。为了消除电子枪热形变的影响,设计了装配模具进行补偿,并得到了实验验证。该电子枪已用于多种G波段行波管,解决了关键部件技术问题。
太赫兹(0.1~10 THz)频谱资源丰富,在高分辨力实时成像、抗干扰保密通信以及高速高数据率传输等方面具有重要的应用前
此外,太赫兹行波管电子枪的热形变量会直接影响电子枪性能。文献[
本文针对G波段(140~220 GHz)太赫兹行波管的电子枪进行了设计与实验研究,分析了电子枪的热形变问题,设计了电子枪装配模具对热形变量进行补偿,通过实验证实了补偿效果,实现了电子枪的设计指标。
根据文献[

图1 皮尔斯电子枪示意
Fig.1 Geometry of Pierce gun
为了提高聚焦极的加工精确度与组装精确度,将

图2 电子枪物理结构
Fig.2 Physical structure of the electron gun
item | rk | rg | ra | Zgk(Fig.11) | Zak |
---|---|---|---|---|---|
value | 0.58 | 0.80 | 0.32 | 0.30 | 6.0 |
tolerance | 0.01 | 0.02 | 0.01 | 0.01 | 0.1 |

图3 电位分布图
Fig.3 Potential distribution profile
采用高导磁的铁镍钴磁封合金作为枪壳材料,既可实现阴极区的磁屏蔽,又保证了枪壳与陶瓷结构的可靠封接,

图4 轴向磁场强度分布
Fig.4 Distribution of axial magnetic field
除了电子枪的电性能设计外,还需要重点关注阴极的温度和电子枪的热形变,以下针对这2点展开探讨。

图5 热阴极发射电流曲线
Fig.5 Emitted current curve of thermal cathode
采用Ansy
(1) |
式中:M为热对流矩阵;C为导热矩阵;R为热辐射矩阵;x为法向温度矢量;b为热载荷矢量。
对于实际工况下的电子枪,以上3种传热方式均存在,据此设置相应的换热边界条件:枪壳外表面设置与空气的自然对流换热;零件焊接区域通过设置绑定接触和热阻实现热传导;电子枪内部为高真空环境,热辐射作用显著,内部零件间设置辐射换热。相应参数设置如
parameter | value |
---|---|
convection coefficient/(W· | 10.0 |
contact conductance(metal-metal)/(1 | 8.0 |
contact conductance(metal-ceramic)/(1 | 3.0 |
radiation emissivity(metal) | 0.2 |
radiation emissivity(cathod) | 0.8 |
由于电子枪的热屏蔽筒厚度仅为0.02 mm,对其采用壳单元进行划分保证网格质量,其余零件采用实体单元四面体网格划分,网格最大尺寸0.6 mm,最小为0.1 mm,保证最小尺寸方向至少包含2层网格单元。模型整体网格单元质量为0.85。模拟了不同热丝功率下的阴极温度,结果如

图6 阴极表面温度模拟值与实验值对比
Fig.6 Comparison of cathode surface temperatures
between simulation and test
装配电子枪样品并进行阴极温度实验。实验中对电子枪组件单独排气,保持内部高真空环境;调整热丝电压和电流,使阴极工作在不同温度。采用红外测温仪对阴极表面温度进行监测,得到热丝功率与阴极表面温度之间的对应关系如

图7 工况下电子枪的温度分布云图
Fig.7 Temperature distribution of electron gun
零件在热载荷作用下会产生形变,由于温度场的不均匀性以及各零件材料热膨胀系数不同,工况下电子枪内部电极尺寸和极间距变化难以解
当阴极表面温度在工作点1 050 ℃时,热形变矢量云图如

图8 工况下电子枪的热形变矢量云图
Fig.8 Vector graph of thermal deformation of electron gun

图9 工况下电子枪的径向热形变
Fig.9 Radial thermal deformation of electron gun

图10 工况下电子枪的轴向热形变
Fig.10 Axial thermal deformation of electron gun
采用CST粒子追踪求解器模拟,
Zgk | I/mA | rw/mm | Zw/mm |
---|---|---|---|
designed value | 50.9 | 0.056 | 10.3 |
with ΔZgk | 70.0 | 0.098 | 14.8 |

图11 电子枪发射情况对比
Fig.11 Contrast of the electron gun emission performance
为消除电子枪热形变的影响,设计了电子枪装配模具,将阴极和聚焦极的装配距离设计为2.93 mm,从而对ΔZgk进行补偿。

图12 电子枪
Fig.12 Electron gun

图13 电子枪发射性能
Fig.13 Emission performance of the electron gun
该电子枪已用于G波段20 W连续波行波管中,在20 kV工作电压下的发射电流为50 mA,电子注流通率达到95
本文设计了用于G波段行波管的电子枪,电子注电压20 kV,电流50.9 mA,注腰半径0.056 mm,射程10.3 mm。仿真结果表明,电子枪的热形变造成阴极和聚焦极轴向间距减小0.07 mm,造成总电流、注腰半径、射程值分别增大了38%、75%、44%,偏离了设计目标。为了消除电子枪热形变的影响,设计了装配模具进行补偿,并得到了实验验证。该电子枪已用于G波段20 W连续波行波管、G波段50 W脉冲行波管中,解决了G波段行波管的关键部件技术问题。
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