The Influence of Window Parameters on the Transmission Characteristics of Millimeter Waves

This work reports about the influence of some window parameters, such as the mechanical tolerance of disk thickness, the variation of distance between two disks, and the frequency drift during gyrotron operation on the transmission characteristics of millimeter waves. Detailed calculations of the transmission characteristics for a single-disk gyrotron window and frequency tunable double-disk plasma fusion torus windows have been performed. The geometry of the window units has been optimized in order to obtain a suitable transmission characteristic, i.e. power reflection less than –20 dB within a frequency bandwidth of about 1 GHz around the chosen frequencies.     

A CVD-Diamond Disk Brewster Window for a Frequency Step-Tunable 1 MW Gyrotron

Output window design is one of the key issues for realizing broadband output of a multi-frequency gyrotron. Corresponding to the recent development of a frequency step-tunable 1 MW gyrotron at FZK, this paper reports about a newly designed ultra-broadband CVD-diamond disk Brewster window. The detailed calculations of mm-wave transmission characteristics are given, and measurement results of the disk loss tangent and its distribution across the disk are also presented. The geometry of the window unit has been optimized to keep the window reflections low over a wide angular range around the Brewster angle.     

提高稳频He－Ne激光器输出功率的研究

稳频Ｈｅ－Ｎｅ激光器的输出功率与谐振腔的损耗密切相关。本文对其中的布儒斯特角窗口带来的附加损耗进行了定量的分析，指出布儒斯特窗片封接引起的各向异性损耗是主要的腔内损耗来源。在实践上采用具有独特优点的锢封接技术，大大提高了布儒斯特窗片的封接质量，从而减小了腔的损耗，提高了稳频Ｈｅ－Ｎｅ激光器的输出功率。比如，腔长为１１０ｍｍ的６３３ｎｍ稳频Ｈｅ－Ｎｅ激光器的输出功率达到２．５～３．０ｍＷ。     

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.     

HL-2A装置ECRH系统传输效率的测量研究

介绍了HL-2A装置ECRH系统传输效率的测量方法。通过对MOU、回旋管输出窗口及真空密封窗口吸收功率的测量,得到HL-2A电子回旋系统的传输效率为90％左右。提出了除由MOU处测量微波功率外,可以由传输线的其他部位确定功率的方法。     

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介绍了HL-2A装置ECRH系统传输效率的测量方法。通过对MOU、回旋管输出窗口及真空密封窗口吸收功率的测量,得到HL-2A电子回旋系统的传输效率为90％左右。提出了除由MOU处测量微波功率外,可以由传输线的其他部位确定功率的方法。     

A forced gas-cooled single-disk window using silicon nitride composite for high power CW millimeter waves

Silicon nitride composite as a candidate of a window material for high power CW (Continuous Wave) millimeter-waves was high power tested especially with a surface cooling by impinging gas nitrogen jets on the single-disk surface. Gas-cooling dramatically suppressed the temperature of the window disk even with gas flow rate of around 100 l/min. With gas cooling of 465l/min., 130kW CW power of HE₁₁ mode could be transmitted through the silicon nitride window with a diameter of 88.9mm. The peak window temperature was completely saturated on 123.6 °C. Without gas-cooling it did not saturate and reached 323 °C during 30 seconds pulse. A possibility of 1MW CW single disk Brewster windows with a forced gas-cooling is discussed, resulting in convinced prospects of the windows with realistic size and thickness.     

Recent results of the 1-MW, 140-GHz, TE22,6-modegyrotron

The TE_22,6-mode gyrotron operated at Forschungszentrum Karlsruhe at a frequency of 140 GHz has been investigated with respect to the behavior of different emitter materials, step tunability and reflections of the output beam. Two different materials of an emitter ring, LaB₆ and a coated dispenser cathode, were used to test the features of the gyrotron. The output power was found to be independent from the cathode material, as long as a new emitter ring was used. Aging of the emitter led to a slightly decreased output power. The gyrotron also was operated with a Brewster window. The broad-band characteristics of this window made it possible to measure the neighboring frequencies in a frequency range extending from 114 to 166 GHz. Only a slight dependence of the output power has been found over the whole frequency range. The Brewster window also allows us to investigate the influence of reflections on the output power. A strong decrease of the output power was found even for very small reflections. Tilting the power calorimeter (the reflections were measured to be less than 1%) increased the output power by about 20% to 1.6 MW at an efficiency of 36.2%. With a collector depression voltage of 35 kV for energy recovery, efficiencies of 60% at the above-mentioned output power were obtained     

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HL-2A装置电子回旋共振加热系统的主要指标是2MW/1s/68GHz,系统由4个单元组成,每个单元包括一只回旋管,微波传输系统,控制保护测量和冷却等子系统。通过对ECRH系统和回旋管的调试,每只管子微波输出功率500kW,脉冲宽度1s,四管并联运行时总输出功率达到1.63MW,系统使用效率高于80%。     

A Multilayer Waveguide Window for Wide-Bandwidth Millimeter Wave Tubes

A multilayer waveguide window is demonstrated to exhibit wide bandwidth and high transmission for applications in high-frequency microwave tubes. A transfer matrix approach is employed to discretize the dielectric function profile of the multilayer heterostructure in a rectangular waveguide. The closed form has been obtained and the corresponding reflection and transmission characteristics have been carried out. The analytical calculation is also compared with the result of numerical simulation via the finite-element code HFSS. The exact calculation agrees with the numerical simulation very well. By comparison, the approach not only enhances the accuracy and efficiency, but also gives a good criterion for the design. The results show that the bandwidth for a transmission of 99%, i.e., S ₁₁ below –20 dB, can be optimized to be about 8.75 GHz at a central frequency of 35 GHz or about 25%. A wide-bandwidth waveguide window can be easily designed for Ka-band and W-band tubes, and even for higher frequency ones.     

D-band frequency step-tuning of A 1 MW gyrotron using a brewster output window

In order to demonstrate the usability of gyrotron oscillators as frequency step tunable high power millimeter-wave sources, experiments on a 1 MW, 140 GHz TE_22,6 gyrotron with a built-in quasi-optical (q. o.) mode converter have been performed. By varying the operating parameters of the tube, a series of oscillations in the frequency range from 114 GHz to 166 GHz were excited. To avoid reflections, caused by the required vacuum barrier window, the gyrotron was equipped with a Brewster window. The achieved output power levels between 0.85 and 1.05 MW are compared to measurements carried out with the same tube using a conventional single-disk window. These experiments showed that even by using a q. o. mode converter, the influence of window reflections on the gyrotron oscillatory behavior cannot be removed completely.     

High power 170 GHz test of CVD diamond for ECH window

In order to check the usability of large-size CVD (Chemical Vapor Deposition) diamond disks for high power millimeter wave vacuum barrier windows at room temperature (T = 293 K) a first series of experiments, using a 170 GHz, 0.4 MW, 0.2 s JAERI/Toshiba gyrotron¹⁾, have been performed. The dielectric loss tangent at a frequency of 170 GHz has been determined to be tan δ = 1.3·10⁻⁴. By comparing the experimental results to numerical simulations the thermal conductivity was estimated to be about k ≈ 1800 W/mK. This preliminary results indicate that a single-disk CVD diamond window assembly using a water-edge cooling could fulfill the requirements for a continuous wave (CW) transmission of millimeter wave power in the megawatt range. This is needed for the Electron Cyclotron Heating (ECH) on the International Thermonuclear Experimental Reactor (ITER).     

低温辐射计的结构优化方案设计

传统低温辐射计的布儒斯特窗口会对传递探测器的绝对光谱响应率定标产生较大的影响。文中阐述了低温辐射计对传递探测器的传统定标过程;分析定标过程中因布儒斯特窗口及窗口复现导致定标精度降低的原因;提出一种新的定标结构。该结构中低温辐射计和传递探测器安置于同心弧形轨道上,二者通过精密电机的控制可以分时切入定标光路,实现传递探测器相对于低温辐射计的绝对定标。新的定标结构能够完全消除布儒斯特窗口在传递探测器定标过程中的影响,降低测量激光功率约50%的不确定度,可以进一步降低辐射定标溯源基准的不确定度,提高定标的精度。     

Travelling Wave Window with Matching Gratings

At millimeter waves, travelling wave dielectric windows are advantageous over commonly used resonant ones due to the higher power capability. An attractive method to compensate the wave reflections from vacuum-dielectric and dielectric-vacuum boundaries is using anti-mirror reflection gratings (Fig. 1) [1]. In this paper, the power loss due to the finite cross-section of the wave beam and the frequency mismatch relative to the resonant value are calulated for the latter type of window.     

布儒斯特角附近的透射光栅传输特性

 减小光栅表面的反射率以得到更高的衍射效率是目前光栅设计与制造中需要解决的重要问题之一。提出利用偏振光沿布儒斯特角入射时具有的特性来实现降低光栅表面反射率的方案,介绍了这种方案的物理模型,并利用严格耦合波分析法进行了模拟计算。计算结果显示,对入射光为TM偏振,波长0.35 μm,当光栅周期较长为2.80 μm时,以布儒斯特角入射的光波,它的表面反射被大大抑制;当光栅周期较短为0.21 μm时也有类似的结论,并且透射光的一级衍射效率极大值出现在刻槽深度为3.50 μm处附近,衍射效率大于95%。     

S波段高功率径向线输出窗的设计

为进一步改进和优化高功率径向线阵列天线的拓扑结构,提高功率容量水平,并满足馈源的真空密封需求,提出并设计了一种适用于高功率径向线阵列天线的微波输出窗。该高功率径向线输出窗采用圆环形陶瓷,材料介电常数为9.4,窗片厚度为3 mm,内径为36 mm,可实现径向线阵列天线馈电系统的输入同轴波导与输出同轴波导间的真空密封。设计结果表明:在中心频率为2.856 GHz下,该径向线输出窗驻波比为1.03,插入损耗为0.17 dB,设计功率容量约150 MW。     

高功率过模圆波导到两路矩形波导功分器

基于模式匹配法分析了高功率过模圆波导到两路矩形波导功分器在传输过程中高阶模式的传输和反射问题,分析得到了高传输效率对过模圆波导的要求,并以此仿真设计了中心频率为2.88GHz的功分器,设计结果表明:在中心频率下反射系数为0.05,对应的圆波导TM01模到矩形波导TE10模传输效率大于99%,真空中功率容量为2.83GW;在2.82~2.94GHz的频带范围内反射系数小于0.1,对应的传输效率大于98%。     

电子束注入简单磁镜中被电子迴旋共振加热捕获的实验研究

在简单磁镜MM-2中,在采用15GHz大功率迴旋管进行电子迴旋共振加热(ECRH)的同时,以不同的方式向磁镜中注入电子束,进行了ECRH捕获电子束的实验研究。结果表明:由于电子束的提前注入,等离子体的预电离时间被大大地缩短。由上ECRH对电子束的捕获,使得热电子环参数得到很大的改善,热电子环的反磁β值约增加62%,对应反磁增加的捕获效率约为(30—40)%。在迴旋管输出约30kW的条件下,适应建立热电环的气体压力窗为(4.67—21.3)×10^-4Pa。 关键词：     

Mixed Fano-SP resonant absorption of THz electromagnetic waves in a photonic resonator contacting with a metal film

In terahertz frequency region, we have investigated theoretically the correlation between spectra of a free photonic structure and that deposited on a metal for several models of metal. It was found that for quasi-normal incidence of p-polarized electromagnetic field the presence of metal generates narrow spectral wells in the middle of reflection windows existing in a free photonic crystal. Quite another manifestation of metal-resonator inter-influence takes place at incident angles exceeding the Brewster angle when reflection spikes coincide with modes of photonic crystal resonator and they are absent throughout the stopband areas. The effects are strongly depended on polarization, number of periods and angle of incidence.     

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68GHz ECRH系统由6套0.5MW/1s(1.5s)子系统构成,140GHz ECRH系统由2套1MW/3s子系统构成。每套子系统由独立的传输线与天线相连,再通过天线注入等离子体。68GHz ECRH子系统为非真空传输线,以内径为80mm的过模波纹圆波导为主要传输部件,包括隔直器、弹性波导、换向波导和一个槽纹深度为l/2的极化器;140GHz ECRH子系统为真空传输线,以内径为63.5mm的过模波纹圆波导为主要传输部件,包括隔直器、弹性波导、换向波导、转换开关、抽气波导和槽纹深度分别为l/4与l/8的极化器。经过不断地完善,68GHz ECRH系统传输线已成功运用于ECRH运行中,整条传输线的输送效率可以达到90%左右。对于140GHz ECRH系统,已完成了传输部件的整体设计,目前正在进行相关部件加工测试。