In this paper, a multigap extended output cavity was designed by 3-D simulations, which served as the output cavity for a W-band sheet-beam extended interaction klystron (SBEIK). In our numerical design, the circuit dimensions were systematically optimized by parametric finite-difference time-domain simulations, and the equivalent circuit for the output cavity was also analyzed. The proper external loading was selected by using a region of loss in 3-D, and the output power was optimized. The results were verified by using the coupler and the waveguide. The 2π mode of the optimized five-gap extended output cavities had an ohmic Q (Q 0 ) of 1343.5, an external Q (Q e ) of 501.6, and a loaded Q (Q L ) of 365.2 at 94.5 GHz. The 3-D particle-in-cell simulations predict that the output cavity of the SBEIK (75 kV and 4 A) can stably produce more than 50 kW of output power using a prebunched beam.

A theoretical model is developed for calculating the eigenmodes of the multi-gap resonant cavity. The structure of concern is a kind of ladder-type circuit, offering the advantages of easy fabrication, high characteristic impedance (R/Q), and thermal capacity in the millimeter wave to THz regime. The eigenfunction expansion method is used to establish the field expressions for the gaps and the coupling region. Then, the match conditions at the interface are employed, which leads to a group of complicate boundary equations in the form of an infinite series. To facilitate the mathematical treatments and perform a highly efficient calculation, these boundary equations are transformed into the algebraic forms through the matrix representations. Finally, the concise dispersion equation is obtained. The roots of the dispersion equation include both the axial modes in the gaps, which include the fundamental and the high-order modes, and the cavity modes in the coupling region. Extensive numerical results are presented and the behaviors of the multi-gap resonant cavity are examined.

大宽高比的非轴对称带状电子注在微波和毫米波真空电子器件中具有显著的技术优势与应用潜力.采用轴向均匀磁场可以聚焦和传输带状电子注,且具有易于实现电子注与磁场的匹配和调节、聚焦强流电子注以及无传输截止电压限制等优点,但面临严重的Diocotron不稳定性.结合单粒子模型理论和冷流模型理论,对带状电子注传输特性进行的研究及其数值计算表明,通过详细设计带状注电子光学系统物理参数,增强聚焦磁场并在传输通道高度方向上选择较大的电子注填充比,可以有效降低Diocotron不稳定性对带状电子注的影响,并实现其长距离稳定传输.通过对应用于W波段带状注器件的电子枪及电子光学系统三维仿真和参数优化,解决了小尺寸和高精度结构所带来的对准、装配和焊接等工艺与技术问题,完成了带状电子注聚焦与传输实验高真空密封束管的研制.实验获得的电子枪压缩和成形的椭圆带状电子注截面为10mm×0.7mm,且在电子注电压为20—80kV,电流为0.64—4.60A时,在长度为90mm的漂移通道内带状电子注传输的通过率达到95%以上.该结果优于目前国际上采用周期永磁聚焦进行带状电子注传输通过率92%的实验结果.