Electromagnetic Analysis and Cold Test of a Distributed Window for a High Power Gyrotron

A novel distributed window for output radiation from a high power 110 GHz gyrotron is made of thin slats of sapphire interleaved and brazed to hollow metal vanes. We report the results of electromagnetic theory and cold test of this distributed window. We calculate the frequency dependence of the reflectivity of a Gaussian beam from the window. The theory indicates a significant frequency shift of the minimum reflectivity with temperature rise of the sapphire slab. This effect is of great importance for high power operation. In cold test, the distributed window reflectivity was measured while the window was heated. The cold test results are in good agreement with the theory.     

A reduced-scale experimental investigation of facade flame behavior ejected from a top-hung window of fire compartment

In case of a room fire, facade flame ejected from a window could lead to catastrophic consequence. Top-hung window is a common feature in modern buildings. This paper investigates, for the first time, the ejected facade flame behavior from a top-hung window. Experiments are performed by a cubic scale model compartment with a top-hung window of four opening angles and four dimensions under various heat release rates (HRR). A total of 119 test conditions are involved to quantify generally the ejected facade flame behavior and morphological characteristics, characterized by its vertical height and horizontal depth (normal to facade). It is found that the position of neutral plane between the inflow and outflow at the top-hung window increases with opening angle, while being smaller as the window width is larger or the window height is smaller. The critical HRR for flame ejection is higher as the top-hung window opening angle is larger. The facade flame depth increases, while the flame height decreases, with increasing of opening angle of the top-hung window. A new characteristic length taking into account both the top-hung window dimensions and window opening angle is deduced by the mass balance analysis of the inflow and outflow as well as ventilation factor through the top-hung window. New dimensionless models are established to describe the critical HRR for flame ejection, the height of the facade flame and flame depth as a function of the newly derived top-hung window ventilation factor as well as characteristic length, showing good fitting of experimental results. The present study provides the basic data, understanding and model of facade flame characteristics from a top-hung window of a fire compartment, which is essential in estimation of its risk and adverse impact to urban environment as a new supplementary over previous knowledge limited for freely opened windows.     

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.     

Two-dimensional phase retrieval using a window function

Two-dimensional phase retrieval by use of a window function is considered. First the uniqueness and the reconstruction of a two-dimensional signal from the Fourier intensities of the three signals, an original signal, the signal windowed by a window w(m, n) , and the signal windowed by its complementary window w(c)(m, n) = 1 - w(m, n) , are addressed. Then phase retrieval without a complementary window is considered. Conditions under which a signal can be uniquely specified from the Fourier intensities of the original signal and the windowed signal by w(m, n) are developed, and a reconstruction algorithm is presented.     

The design and construction of a VUV Ar-arc source and a VUV monochromator

The design and construction of a VUV source and a VUV monochromator is reported. The reliability of the VUV source suggests that it can be used as a VUV high radiance transfer secondary standard. A VUV window is used to isolate the high pressure argon-arc source from the VUV monochromator. The spectrum is therefore limited by the transmission cut-off of the window. Alternatively, a differential pump could be used to extend the wavelength range to the extreme UV and eliminate the uncertainties associated with the aging effects of the VUV window. The apparatus is to be used to measure the VUV spectra of certain glass samples.We wish to acknowledge the financial support by SERC under research grant number GR/E 01973.     

Mechanical research and development of a monocrystalline silicon neutron beam window for CSNS

The monocrystalline silicon neutron beam window is one of the key components of a neutron spectrometer. Monocrystalline silicon is brittle and its strength is generally described by a Weibull distribution due to the material inhomogeneity. The window is designed not simply according to the mean strength but also according to the survival rate. The total stress of the window is stress-linearized into a combination of membrane stress and bending stress by finite element analysis. The window is a thin circular plate, so bending deformation is the main cause of failure and tensile deformation is secondary and negligible. Based on the Weibull distribution of bending strength of monocrystalline silicon, the optimized neutron beam window is designed to be 1.5 mm thick. Its survival rate is0.9994 and its transmittance is 0.98447, which meets both physical and mechanical requirements.     

一种废束站束窗结构设计与优化

废束站束窗是废束站的重要部件。利用束流的束斑尺寸及功率确定束窗能量的高斯分布方式;通过蒙特卡罗方法计算束窗的沉积能量。利用ANSYS稳态分析确定束窗的材料、截面形状和厚度。通过计算比较束窗在不同材料、截面形状和厚度条件下的温度、应力和变形,得出合适的束窗材料、截面形状和厚度,从而确定束窗的最终结构。最后利用瞬态方法模拟束窗调束时的温度分布情况。     

Three-dimensional analysis of a vacuum window connected towaveguide

For an effective additional heating system in the experimental tokamak-type system the pillbox-type vacuum window is proposed to isolate each part. L.J.B. Bergeron's formulation (1941) of the pillbox-type vacuum window connected to cylindrical waveguides is described, and the fundamental characteristics of the electromagnetic field within this system are shown. Local heating at the surface of the dielectric disk may be decreased by reducing circumferential dependence by using cylindrical waveguides. A unified analysis involving the pillbox window and both the input-side waveguide and the output-side one has been performed using the presented method. The results obtained present the complex variations of the distribution of the field in the overall analyzed region as a function of the length of the pillbox window. These results illustrate the characteristics of the three-dimensional analysis. The analyzed model is described; in particular, the boundary conditions of the conductor are explained. The numerical results of the field distributions are shown by the longitudinal magnetic field variations and the electric field variations in the various cross sections in the pillbox window     

Numerical analysis and passive control of a car side window buffeting noise based on Scale-Adaptive Simulation

Flow over an open side window in a car exhibits similar characteristics as the flow over an open cavity. Computational Fluid Dynamics (CFD) simulation over a cavity was done as a benchmark. The unsteady flow simulation was carried out using Scale Adaptive Simulation (SAS) turbulence model. The benchmark results, frequency and sound pressure levels of feedback and resonance modes, all well matched with the experimental data. Then, with the right rear window, for example, the mechanism of the side window buffeting was investigated. The simulation results show that side window buffeting noise is generated by large scale vortices and in low frequency. Furthermore, buffeting noise characteristics under several patterns of side windows opening were also numerically investigated. As a result, rear window buffeting noise is more severe than that of front window when one window open, and combination pattern of side windows open can reduce buffeting noise. To decrease the interior noise and improve car ride comfort, four suppression measures through adding a side window weather deflector at the A-pillars, constructing a cavity at the B-pillars, combination of the front and rear windows and installing a row of square cylinder deflector at the B-pillars were also studied, respectively. In conclusion, certain noise reduction can be achieved through four passive control methods.     

Temporal window shape as a function of frequency and level

In an earlier article [Moore et al., J. Acoust. Soc. Am. 83, 1102-1116 (1988)], preliminary work on the temporal-window model of temporal resolution in the auditory system was described. The temporal window is conceived of as a temporal integrator that slides in time and that is implemented as an intensity-weighting function. The shape of the temporal window was estimated by measuring the threshold for a brief sinusoidal signal presented in a temporal gap between two bursts of noise as a function of the duration of the gap and the position of the signal within the gap. In this paper, a much more thorough examination of the effects of level and frequency on the shape of the window is presented, using the same basic technique. Temporal window shapes were measured at four different frequencies (300, 900, 2700, and 8100 Hz) and at three different masker levels covering a 20-dB range at each frequency. The shape of the temporal window was well described by modeling each side as the sum of two rounded-exponential (roex) functions. The equivalent rectangular duration (ERD) of the window decreased from about 13 to 9 ms as the center frequency increased from 300 to 900 Hz, but decreased only slightly, to 7 ms, as the center frequency increased to 8100. The greater ERD at 300 Hz does not seem to be explicable in terms of "ringing" in the auditory filter. The ERD decreased somewhat with increasing level, for example, having a value of about 10 ms at 2700 Hz with a 20-dB masker spectrum level and about 7 ms with a 40-dB masker spectrum level.     

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.     

Electronic Transport through a Waveguide in the Presence of a Magnetic Obstacle

By means of the transfer matrix technique, the electronic transport through a quantum waveguide in the presence of a magnetic obstacle is investigated theoretically. By comparing the calculated conductance spectra of the opposite spin electrons, we find that there exists a notable spin filtering window in the low energy region. Dependences of such a spin filtering window on the size, position and potential strength of the magnetic obstacle are studied in detail.     

Technique of Measuring the Relative Surface Figure of a Nontransparent Window Plate Using Visible Light

An interferometric technique to measure a nontransparent window plate using visible light is proposed. Using this technique, the relative surface figure of one surface with respect to another can be measured. The relative surface figure also includes the parallel of both surfaces of the window plate. The optical performance of a nontransparent window plate as an optical component can be evaluated accurately without using infrared light sources if the relative surface figure of the plate is measured.     

一种高重频废束桶束窗的设计及热结构分析

深圳中能高重频X射线自由电子激光（S3FEL）将建设成为全球唯一软X射线波段的高重频自由电子激光。废束桶是S3FEL装置的重要设备,在系统调束中发挥着重要作用。废束桶束窗是废束桶的重要组成部件,用于隔离和保护加速器超高真空环境。本文对几种常用的废束桶束窗材料进行了对比分析,最终选择铍作为束窗的材料,并依此设计了一种带有水冷结构的束窗。通过蒙特卡罗方法计算得到不同厚度束窗的沉积功率,采用有限元分析方法对不同厚度的束窗进行热结构计算与分析,得到厚度为1.6 mm的水冷铍窗效果最佳,其最大温度为121.6℃,低真空为1 Pa时的最大应力与中心变形分别为198.7 MPa和0.000 82 mm,低真空为101 325 Pa时的最大应力与中心变形分别为204.2 MPa和0.097 mm,结果均满足使用要求。此研究为S3FEL的废束桶束窗设计提供了重要的理论依据。     

The development of a diamond switch for RF pulse compressionsystems

The use of a diamond RF switch for super-highpower microwave/millimeter wave generation has been evaluated. An X-band chemical vapor deposition (CVD) diamond window package was theoretically analyzed, designed, and built. Thirty-eight percent of an injected microwave signal with a frequency of 11.424 GHz was reflected from a 100-μm thick, 22-mm-diameter CVD diamond window when activated by a 160-mJ, 266-nm Nd:YAG laser. The details of the CVD diamond window design and experimental results are presented. The results have high application potential for building super-high-power microwave systems     

Controlled acceleration of a modulated quantum bouncer

Cold atoms bouncing on a modulated atomic mirror exhibit dynamic localization and acceleration subject to modulated strength. We explain the characteristics of acceleration using accelerated mapping and define control parameters. We show that the effective Planck’s constant plays a vital role in limiting overall linear growth of accelerated atoms with time. For large values of the effective Planck’s constant, the atomic quantum accelerated is seized if the localization window overlaps the accelerated window.     

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结合陶瓷窗设计相关理论,采用电磁场仿真软件(CST)和有限元分析软件(Ansys),仿真计算了低杂波传输线系统新陶瓷窗的电磁和热力学性能。设计的陶瓷窗采用BeO陶瓷作为介质窗体,在中心频率点附近300MHz以上的带宽内,其驻波比小于1.1,窗片中心的最大温升为11.7°C。     

Analyzing the Switching Characteristics of a NOLM Demultiplexer with on Analytic and Numerical Methods

The switching characteristics of a NOLM demultiplexer are investigated by using an analytic and numerical methods. The results reveal that the switching characteristics of a NOLM demultiplexer depend on parameters such as the power coupling ratio of the coupler,the peak power of control pulses,the walk-off and the initial time delay between signal pulses and control pulses,etc. The efficiency of NOLM is dependent on the peak power of control pulses. However,the switching window profile begins to oscillate as the power exceeds a critical value and this will be detrimental to the demultiplexed signals. The signal-control pulse walk-off can broaden the switching window of NOLM,make the window profile deviate from its central position,and decrease its switching efficiency.     

Analyzing the Switching Characteristics of a NOLM Demultiplexer with on Analytic and Numrical Methods

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Multipactor discharge on a dielectric surface in the field of circularly polarized plane waves

The secondary-emission discharge (multipactor) on a dielectric surface irradiated by a plane TEM wave of circular polarization is analyzed theoretically. It is shown that interaction of electrons with the electromagnetic wave field can provide their return to the emission surface, which makes a multipactor possible even without any external static fields. Multipactor conditions for different reflection coefficients of the incident wave are found. The obtained results are used to estimate the throughput of the output window of a high-power vacuum microwave device. Specifically, it is established that decreasing the high-frequency field amplitude on the window surface when the mode of a partially standing wave is realized in the vicinity of the window does not always help raise its electric strength.