X波段盒形输出窗频率特性的改进

该文首先详细阐述了判别输出窗鬼模的原则和方法,然后以一个X波段输出窗为例介绍如何应用三维电磁场计算软件微波工作室对输出窗进行改进,计算与冷测均得到了较好的结果,可以满足实际需要,对输出系统的设计具有很高的参考价值。     

高功率毫米波回旋行波管宽带输出窗设计

首先利用场匹配理论建立传输级联矩阵对回旋行波管输出窗进行解析分析。在理论分析的基础上,通过数值计算得到回旋行波管宽带蓝宝石输出窗的初步结构和尺寸,然后利用三维高频分析软件HFSS进行仿真验证。通过大量计算与仿真,为Ka波段TE01模回旋行波管设计出驻波比小于1.2的输出带宽约为6GHz,相对带宽大于17%的高性能3层窗片结构蓝宝石输出窗。通过冷测实验研究表明仿真计算结果与冷测结果基本一致。     

Ka波段TE_（01）模回旋速调管带新型渐变段输出腔设计

利用正余弦拟合的方法和半径渐变波导的耦合波理论,设计出一种Ka波段TE01模回旋速调管带该新型渐变段输出腔。通过Matlab数值计算和HFSS仿真优化,研究了该新型渐变段的传输参数、反射参数、对杂模的抑制等性能指标。仿真结果表明：在渐变段长度为80mm、口径由14mm变化到32mm的情况下,在33～35GHz的范围内该新型渐变的传输参数大于-0.016dB,反射参数小于-55dB,对TE02模的耦合为-25dB和对TE03模抑制在-55dB以下;而该输出腔的中心频率为34.075GHz,Q值为109.6,工作模式TE01模式的模式纯度大于0.94。     

L波段10 MW同轴腔多注速调管双端口输出系统的研究

该文对L波段10 MW多注速调管输出系统开展了模拟和实验研究。计算分析了新型双端口6注同轴输出腔谐振频率、品质因数、特性阻抗等高频参数;设计了扁波导耦合输出窗,在波导内设置金属杆以调节阻抗匹配,使输出窗在工作频点1.3 GHz的驻波比计算值小于1.01,驻波比1.2以下带宽为100 MHz;加工了输出系统实物,开展了冷测实验,实验值与设计值吻合良好;利用PIC软件对输出系统注-波互作用特性进行了计算,获得了大于10 MW的输出功率,计算注-波转换效率大于65%。     

Ku波段1 MW小型化高峰值功率多注速调管

介绍了一种Ku波段1 MW小型化高峰值功率多注速调管的研制。通过对高性能电子光学系统、TM₄₁₀模式高频系统设计以及高峰值功率输出窗在内的多个关键技术作了详细分析和介绍,总结了速调管的设计方法,最终实现良好的电子注动态流通率、50 MHz以上的输出带宽及1 MW以上的功率输出。设计过程和结果可指导其它同类型Ku波段高峰值功率多注速调管的设计。     

一种Ka波段回旋行波管输出窗设计

针对Ka波段回旋行波管输出窗介质窗片易打坏的问题,引入了3层介质厚窗结构和液冷结构。利用微波网络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,给出Ka波段回旋行波管一种新型中间液冷结构输出窗的参数,通过CST进行仿真验证和优化处理,并进一步结合热损耗公式和ANSYS Workbench对输出窗进行热分析,在26.3~35.7 GHz频带范围内,实现S_(21)>-0.5 d B。     

8mm回旋速调管放大器高频窗的设计

采用三维电磁软件给出了8mm输入、输出窗的设计.其中输入窗采用矩形窗,频率为34～36GHz,驻波比小于1.08.输出窗频率为34.4～35.4GHz,驻波比小于1.2.文章讨论了介质厚度和相对介电常数对窗片反射系数的影响.     

采用圆锥形陶瓷大功率微波输出窗的模拟分析

该文尝试利用一种圆锥形陶瓷盒形输出窗,改善大功率微波输出窗的匹配特性、功率承受性能和热耗散能力。采用Ansoft HFSS三维计算软件分析了此类陶瓷输出窗的基本电气和热耗散性能,对大功率输出窗的工程设计很有意义。     

P波段小型化6MW高效率多注速调管的研制

介绍了一种P波段小型化6MW高效率多注速调管的研制方案,目前该管在P波段已经实现脉冲输出功率6.1 MW,效率68%。通过周期反转永磁聚焦、BAC法结合CSM法优化群聚提高互作用效率、大功率同轴输出窗等关键技术的应用,解决了高效率、高峰值功率容量和高可靠性等难题。     

Ka波段高功率基波回旋速调管高频系统研究

对Ka波段、工作模式为TE021,模的基波高功率回旋速调管的高频结构进行了研究.讨论了群聚腔两端突变对TE02模反射相位和幅值,以及绕射产生的TE01模的相位和幅值的影响;TE01模相干迭加效应和对TE02模场分布形式的影响,通过粒子模拟计算研究了最具破坏性的杂模.优化设计了腔体的尺寸,使得既降低了TE01模对工作模TE02模的影响又有效抑制了最具破坏性的杂模,并得到了34GHz的TE021模四腔回旋速调管放大器设计方案.PIC计算表明:在工作电压70kV,注电流20A,电子横纵向速度比为1.5时,中心频率33.97GHz,输出功率720kW,相对带宽1.5%,电子效率51.4%,饱和增益大干49.7dB.     

High power millimeter-wave TE03 to TM11 mode converters

Transmission of power from 42 ± 0.2 GHz gyrotron (TE₀₃ mode) to tokamak or dummy load requires a set of transmission line components. It includes a set of mode converters that converts circularly unpolarised TE₀₃ mode to polarised HE₁₁ mode. The mode conversion sequence is methodised in two steps; first from TE₀₃ to TE₀₁ mode and then from TE₀₁ to TM₁₁ mode. The proposed mode converters performance depends on the parameters such as waveguide radius, beat wavelength, number of ripples, its perturbation amplitude (η) and bending angle. These parameters are numerically optimised and verified in CST microwave studio. TE₀₃ to TE₀₁ mode conversion is realised by the generation of intermediate mode TE₀₂. The mode conversion length for TE₀₃ to TE₀₂ mode converter is6λ₀, (where λ_b is the beat wavelength of corresponding mode conversion) which converts 99.15% of an incident circular TE₀₃ mode power into TE₀₂ mode power. Next, mode converter converts TE₀₂ mode into TE₀₁ mode with 99.06% efficiency along the optimal length of6λ_b. For TE₀₁ to TM₁₁ mode conversion, two conversion methodologies have been proposed: first using axis arc bend (34.94°) technique to convert TE₀₁ into its analogous degenerate mode with 99.01% conversion efficiency and second using parabolic curve with 90° bend, which gives a conversion efficiency of 97.5%.     

Efficient Output Mode Converter for 30 GHz Gyroklystron at IAP

An output mode converter for Ka-band multi-MW gyroklystron in the Institute of Applied Physics (IAP) operating in the TE₅₃ mode is suggested. Two variants of the converter, aimed for different applications, are presented: the TE₅₃ to TE₀₁ mode converter with power output along the device axis and the TE₅₃ mode to Gaussian wavebeam quasi-optical converter with a visor. The suggested designs include the built-in electron beam collector. The converters were designed using a new synthesis algorithm, which implies iterative improvement of the waveguide wall shape in order to achieve high efficiency. The calculation results were proven by HFSS simulation and low-power tests of one version of the converter.     

THE DESIGNS OF HIGH EFFICIENCY LAUNCHER OF QUASI-OPTICAL MODE CONVERTER FOR HIGH POWER GYROTRONS

A high efficiency launcher of quasi-optical (QO) mode converters for high power gyrotrons have been designed and tested. A helical cut launcher radiates the RF power via its straight cut onto the first phase correcting mirror. The launchers have been optimized for the TE_31.8 mode at 170 GHz and TE_22.6 mode at 110 GHz by numerically optimizing a launcher surface. The helical cut of the launcher has been optimized by taking the taper angle into account. Further more, the amplitude of the surface perturbation have been optimized for improved focusing in order to reduce the diffraction losses at the helical cut. Low power measurement shows a good agreement with the design. High efficiency characteristics of the design have also been calculated on the assumption of frequency downshift due to the thermal expansion of the cavity and stepwise frequency tuning by changing the operating mode. Besides, the possibility of high efficiency launcher for higher mode is discussed, and these results give the prospect to high efficiency long pulse gyrotrons.     

High-power Mode Converter of Overmoded Bent Circular Waveguide

Based on the mode coupling theory, a TE₀₁—TM₁₁ mode converter was designed and optimal results were obtained. In this paper, bandwidth of mode converter with axis exponential structure is the largest, and mode converter with axis sinusoidal structure is the most compact in the case of the center frequency is 28GHz and the waveguide radius is 16mm. If the bending angle between input port and output port of mode converter was demanded for 90°, mode converter with axis parabola structure had the characteristics of compact structure, higher mode purity and larger relative bandwidth. Meanwhile, we found that the converter could be also used as TE₁₁ mode transition with transmission efficiency above 99%. But due to bending angle of this structure was restricted, its center frequency and waveguide radius had the obvious corresponding relation.     

Design of a 94 GHz transition section with cosinusoidal profile

Up to now, many transition sections have been designed and applied successfully. But a transition section with cosinusoidal profile, its operation principle and how to design it have not been found in available literature until now. In this study, a transition section with a cosinusoidal profile and the method to design it are proposed based on the operational principles of mode converters with similar profiles. A 94 GHz transition section used to transmit TE₀₁ mode efficiently is designed using the method. The calculations by our codes and simulations on a high-frequency structure simulator indicate that the section can transmit TE₀₁ mode with transmission efficiency over 0.987 (within a bandwidth of 7.6 GHz) and reflection below ?40 dB. Experimental results show our design is successful. Comparison between the section and the linear one shows that the former is much shorter than the latter when they are used to transmit TE₀₁ mode at the same characteristics above. Such a strong point of shorter length is very helpful for the construction of a compact microwave device.     

High power mode conversion for linearly polarized HE11 hybrid mode output

Efficient plasma heating by ECR-wave irradiation requires axisymmetric, narrow, pencil-like millimetre wave beams with well-defined polarization. The linearly polarized gaussian-like HE₁₁, mode satisfies these conditions best. This quasi-optical hybrid mode can be generated from TE_0n gyrotron mode compositions by the two multi-step mode conversion processes: (1) ΣTE_0n to TE₀₁ to TE₁₁ to HE₁₁ or (2) ΣTE_0n to TE₀₁ to TM₁₁ to HE₁₁. The first scheme has the advantage that the converters can all be made without bends, allowing an arbitrary choice and fast change of the polarization plane. The second scheme does not exhibit this advantage, but it is more suitable at very high frequencies (e.g. 140GHz) because efficient TE₀₁-to-TM₁₁ transducers can be made considerably shorter than serpentine TE₀₁-to-TE₁₁ mode converters. This paper presents computations on mode converter systems of the first type at 70GHz and of both types at 140GHz (ID = 27 · 8 mm for 200kW transmission lines). The structure of wall perturbations (phase-matched superposition of 2 or 3 different geometrical periods) in the rippled wall mode converters and the curvature distribution in the bent, smooth-walled TE₀₁-to-TM₁₁ mode transducer were optimized by numerically solving the corresponding coupled-mode differential equations. Computer-aided optimization of circumferentially corrugated mode converters has been achieved with a scattering matrix code employing the modal field expansion technique (modular analysis concept (MAC)). In all cases the predicted overall efficiency of the complete mode converter system from ΣTE_0n (predominantly TE₀₂ at 70GHz or TE₀₃ at 140GHz) to HE₁₁ in the desired polarization is approximately 95% at 70GHz and 92% at 140GHz (ohmic attenuation is included). Low-power measurements on the conversion efficiency of the various mode transducers are in excellent agreement with the predicted values. High-power operation has been successfully demonstrated using a pulsed 70GHz gyrotron (200kW, 100ms).     

Thermo-Mechanical Analysis of Single-Disc Edge-Cooled Silicon Nitride Millimeter Wave Window for 200 kW CW Gyrotrons

This paper investigates the possibility of using Silicon Nitride Composite (Kyocera SN-287) as single-disc, edge-cooled window for gyrotrons operating below 200 kW CW in the frequency range 28-42 GHz. Rotationally symmetric TE_0n, and TEM₀₀ Gaussian modes of rf transmission through the window have been considered. Analysis performed using a one dimensional (1D) finite difference (FD) code reveals that thermal stresses developed due to non-uniform temperature distribution on the disc surface are well within manageable limits for a 200 kW 42 GHz gyrotron proposed for some ECRH applications. For industrial gyrotrons, for microwave material processing and operating at a maximum power level of 100 kW CW, Si₃N₄ windows may be a cost effective replacement for sapphire windows. It is found that a TE₀₂ profile results in lower peak temperature at the window disc in comparison to a Gaussian beam profile and allows the use of smaller discs.     

Detailed Consideration of Experimental Results of Gyrotron FU CW II Developed as a Radiation Source for DNP-NMR Spectroscopy

A CW gyrotron for the sensitivity enhancement of NMR spectroscopy through dynamic nuclear polarization has been designed. The gyrotron operates at the second harmonic and frequency of 394.6 GHz with the main operating mode TE_0,6. Operating conditions of other neighboring cavity modes such as TE_2,6 at frequency of 392.6 GHz and TE_2,3 at frequency of 200.7 GHz were also considered. The experimental conditions of the gyrotron at low and high voltages are simulated. The output power of 56 watts corresponds to the efficiency of 2 percent at low voltage operation and frequency of 394.6 GHz is expected.     

Rippled wall mode converters for circular waveguide

We present the general theory of rippled wall mode converters. Coupling coefficients for TE and TM waves, of both fixed and rotating polarizations, are calculated. The waveguide ripples considered may be axisymmetric, fluted or helical. We describe in detail a 97% efficient TE₀₄/TE₀₁ converter designed for use with a 35 GHz gyrotron. Cold test results confirm its performance.     

High-power millimetre-wave mode converters in overmoded circular waveguides using periodic wall perturbations

This work reports on measurements and calculations (coupled mode equations) on the conversion of circular electric TE_0n gyrotron mode compositions (TE₀₁ to TE₀₄) at 28 and 70 GHz to the linearly polarized TE₁₁ mode by means of mode converter systems using periodic waveguide wall perturbations. Mode transducers with axisymmetric radius perturbations transform the TE_0n gyrotron mode mixture to the more convenient TE₀₁ mode for long-distance transmission through overmoded waveguides. Proper matching of the phase differences between the TE_0n modes and of lengths and perturbation amplitudes of the several converter sections is required. A mode converter with constant diameter and periodically perturbed curvature transfers the unpolarized TE₀₁ mode into the TE₁₁ mode which produces an almost linearly polarized millimetre-wave beam needed for efficient electron cyclotron resonance heating (ECRH) of plasmas in thermonuclear fusion devices. The experimentally determined TE_0n -to-TE₀₁ conversion efficiency is (98 ± 1)% at 28 and 70 GHz (99% predicted) while the TE₀₁-to-TE,, converter has a (96 ± 2)% conversion efficiency at 28 GHz (95% predicted) and (94 ± 2)% at 70 GHz (93% predicted) with ohmic losses included in each case. This paper also presents theoretical and experimental results on the two-step TE₁₆-to-TE₁₂-to-TE₁₁ mode conversion at 28 GHz by means of two periodically rippled-wall mode converters. The conversion efficiencies achieved are almost 92% and 95%, respectively. Similar converters might be used for transformation of the output modes of future high-frequency TE_1n gyromonotrons or 10 GHz gyro-klystron amplifiers into the TE₁₁ mode, which in turn can then be transformed by circumferentially corrugated or dielectrically coated mode transducers into the perfectly linearly polarized quasi-optical HE₁₁ hybrid mode. The efficiency of periodically modulated wall mode-converters can be considerably improved by proper re-matching of the phase difference between the two converted modes within the converter.