次级结构参数对高温超导直线感应电机电磁特性的影响

次级结构参数对高温超导直线感应电机电磁特性具有重要的影响。分别对次级导电板的材料和厚度对高温超导直线感应电机电磁特性的影响进行研究分析。首先复合次级结构包括导电板和导磁板,分别选择铝板和铜板作为导电板,背铁材料作为导磁板,分别对两种材料在电磁推力、垂向力以及高温超导绕组所受最大垂直场方面做了分析,最终选择了铝铁复合次级结构。然后针对铝铁复合次级特性,通过改变铝板的厚度,来研究铝板的厚度对电磁推力、垂向力、超导绕组所受最大垂直场以及最大通电电流等参数的影响。分析结果表明合适的次级板材料和结构有利于改善高温超导直线感应电机的综合性能。     

HTS磁悬浮电磁发射系统中直线电机起动性能研究

在高温超导(HTS)磁悬浮电磁发射系统中,采用长初级双边直线感应电机进行驱动.同单边直线电机相比,双边直线感应电机由于对称的初级结构,次级结构所受的垂直力为零,这大大提高了直线电机的驱动性能和稳定性.利用旋转电机的经典分析方法,分析了长初级双边直线感应电机不同绕组分布时的绕组因数.结果表明,当采用分布式短距绕组时,可以有效的抑制合成气隙磁场中的谐波分量,改善气隙磁动势波形,进而提高电机的性能和效率.通过Ansoft Maxwell软件仿真求解了6种不同绕组分布时的电机气隙磁场分布,分别求解了整距和分布式短距绕组的电机起动推力,验证了理论分析的正确性.最后,设计制作了分布短距实验样机,并对起动推力进行了测试.结果表明电机起动推力平稳,为复合HTS磁悬浮电磁发射系统设计提供参考.     

HTS磁悬浮电磁发射系统中直线电机起动性能研究

在高温超导(HTS)磁悬浮电磁发射系统中,采用长初级双边直线感应电机进行驱动.同单边直线电机相比,双边直线感应电机由于对称的初级结构,次级结构所受的垂直力为零,这大大提高了直线电机的驱动性能和稳定性.利用旋转电机的经典分析方法,分析了长初级双边直线感应电机不同绕组分布时的绕组因数.结果表明,当采用分布式短距绕组时,可以有效的抑制合成气隙磁场中的谐波分量,改善气隙磁动势波形,进而提高电机的性能和效率.通过Ansoft Maxwell软件仿真求解了6种不同绕组分布时的电机气隙磁场分布,分别求解了整距和分布式短距绕组的电机起动推力,验证了理论分析的正确性.最后,设计制作了分布短距实验样机,并对起动推力进行了测试.结果表明电机起动推力平稳,为复合HTS磁悬浮电磁发射系统设计提供参考.     

真空管道HTS磁浮实验系统中直线电机复合次级研究

在真空管道HTS磁浮实验系统中,利用高温超导体为列车提供悬浮力,闭合圆环形长初级直线感应电机进行驱动,列车加速性能取决于直线电机产生的最大推力.本文结合真空管道的特性,建立了复合次级直线电机模型,利用分层理论模型分析了复合次级参数对电机启动推力及法向力的影响,并通过有限元仿真分析验证直线电机驱动特性与复合次级参数之间的关系.结果表明,采用1.3 mm厚的次级铝板和1 m~2 mm厚的背铁组成的复合次级,列车可以获得较高的启动推力,在运行过程中获得较大加速度,并有效削弱了法向吸力,提高了列车运行时的稳定性,最后通过实验测试,验证了仿真研究的正确性,为高速真空管道HTS磁悬浮列车应用提供设计参考.     

轨道交通用高温超导直线感应电机电磁分析

设计研究了一种用于轨道交通的新型高温超导直线感应电机模型。并结合轨道交通用直线感应电机的实际运行状况,利用ANSYS软件对超导直线感应电机模型进行电磁分析。获得电机内部的磁场分布规律;并研究了电磁气隙、次级材料及次级感应板厚度对电机电磁推力的影响。最后在相同运行条件下,将传统铜绕组电机与高温超导电机做了比较,超导直线感应电机在电磁推力上有优势。     

基于ANSYS的供电频率对高温超导直线感应电机性能影响的分析

通过对高温超导直线电机的理论分析,从内部电磁场的角度出发,研究供电频率的变化对高温超导直线电机的各项电磁性能影响。利用ANSYS有限元分析软件对电机的电磁场、电磁推力以及热损耗进行仿真,并对仿真结果进行简要说明。文中的研究结果对高温超导直线感应电机的运行参数设计提供了理论依据和分析基础。     

空芯大气隙高温超导直线电机电磁力实验研究

直线电机是一种无需中间传动装置而直接将电磁力转换为线性运动的特种电机,在交通运输领域具有广泛的应用前景.将高温超导技术与电机理论相结合,能够有效利用超导材料的强载流能力与高场特性提高直线电机的输出能力.本文提出了一种应用于超导磁悬浮列车牵引的空芯高温超导直线电机,首先建立空芯高温超导直线电机的二维有限元模型对电机结构参数进行初步探索,并完成了超导直线电机样机的设计与制作.通过搭建实验测试平台完成了空芯高温超导直线电机定子磁场和电磁力的实验测试.有限元计算结果与实验数据有较好的一致性,验证了模型的有效性,并利用该模型研究了定子电流,超导线圈电流以及电机气隙对电机推进力输出的影响.本文的相关成果将促进超高速磁浮交通领域关键驱动技术的研究与发展.     

两种减少高温超导风机交流损耗的结构优化方法

超导线圈的制冷问题是高温超导(HTS)风力发电机研究中的一个重点,尤其是在使用接触式制冷的超导电机中,现有制冷机的制冷功率普遍较低,这就要求超导线圈的交流损耗不能太大。在超导风力发电机中,为了减少交流损耗,通常将超导线圈放置在转子中作为励磁线圈使用。在定子齿部材料为铁磁材料的旋转电机中,气隙磁场会发生畸变,转子旋转时超导线圈处会出现交变磁场,产生交流损耗。通过有限元软件仿真,以使用接触式制冷系统的2.5MW高温超导风力发电机为研究对象,证明使用铁磁材料的定子齿部结构是造成超导线圈处交变磁场和交流损耗的主要原因。采用均一化模型计算交流损耗,提出两种减小交变磁场和交流损耗的结构优化方法,即定子齿部采用非磁性材料和在气隙处增加磁屏蔽层。     

两种减少高温超导风机交流损耗的结构优化方法北大核心

超导线圈的制冷问题是高温超导(HTS)风力发电机研究中的一个重点,尤其是在使用接触式制冷的超导电机中,现有制冷机的制冷功率普遍较低,这就要求超导线圈的交流损耗不能太大。在超导风力发电机中,为了减少交流损耗,通常将超导线圈放置在转子中作为励磁线圈使用。在定子齿部材料为铁磁材料的旋转电机中,气隙磁场会发生畸变,转子旋转时超导线圈处会出现交变磁场,产生交流损耗。通过有限元软件仿真,以使用接触式制冷系统的2.5MW高温超导风力发电机为研究对象,证明使用铁磁材料的定子齿部结构是造成超导线圈处交变磁场和交流损耗的主要原因。采用均一化模型计算交流损耗,提出两种减小交变磁场和交流损耗的结构优化方法,即定子齿部采用非磁性材料和在气隙处增加磁屏蔽层。     

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在现场完成发电机定子铁心叠片及紧压工作后,必须进行发电机定子铁心磁化试验以便检查铁心叠片是否有短路及螺栓是否压紧等。通过给缠绕在定子铁心上的励磁绕组通入交流电流,从而在铁心内部产生铁心损耗,使铁心发热,通过测量铁心各部温升根据试验标准判断铁心是否合格。由于300MVA脉冲发电机的工作频率是变化的而非常规的50Hz工频,因此通过计算获得了变频67Hz和99.6Hz下定子铁心的单位铁损耗。脉冲发电机的定子铁心磁化试验结果表明定子铁心装压质量及绝缘是合格的。试验结果为变频率工作的发电机的铁心磁化试验提供参考。     

Guided-Wave Two-Dimensional Acousto-Optic Scanner Using Proton-Exchanged Lithium Niobate Waveguide

Two-dimensional scanning of a 0.6328 mum guided-light beam has been realized using noncolinear acousto-optic (AO) coplanar Bragg diffraction together with colinear AO guided-mode to substrate radiation-mode conversion in a Z-cut Xpropagation LiNbO3 proton-exchanged (PE) waveguide. The two surface acoustic (SAW) waves utilized are at the center frequencies of 500 and 200 MHz, propagating in the Y and X axes, respectively. Two-dimensional scanning of approximately 720 resolvable light beam spots, namely, 18 40 (horizontal vertical) scanning, has been demonstrated using a light beam of 1.0 mm aperture. The total number of resolvable beam spots can be greatly increased from 720 by simply utilizing SAW transducers of larger bandwidth and a light beam of greater aperture. It should also be possible to significantly increase the diffraction efficiency from 3 % by optimizing the parameters of the PE waveguide and the SAWs.     

Femtosecond Transform-Limited Pulse Generation by Compensating for the Linear Chirp of SPM Spectra in Dispersion Shifted Fibers

A simple technique of pulse compression, based on the linear chirp compensation of self-phase modulation (SPM) spectra in dispersion shifted fibers, is demonstrated. The optimization procedure is carried out, for a short span of a single-mode fiber, using a parabolic law, which describes the behavior of the squared output pulse width versus the pump peak power in the case of Gaussian pulses. The experimental results give a minimum pulse duration of 233 fs, which is in good agreement with the model. Shorter and coherent pulses, down to 90 fs, have been obtained by inserting an interference filter at the optical output.     

Effect ofγ-radiation on the spectral luminescence characteristics of impure cadmium tungstate crystals

Results of a study of the effect of γ-radiation on the spectral luminescence properties of cadmium tungstate crystals doped with silver, bismuth, and molybdenum cations are presented. Spectral characteristics of the nondnnnoped crystals are briefly described. Absorption and photo and X-ray luminescence spectra of the crystals taken before and after exposure to γ-radiation (5.5·10⁴ Gy) are compared. It is found that the spectral characteristics of the crystals doped with silver, bismuth, and molybdenum cations do not change markedly after the exposure. The relation between the type of impurity-induced defects, individual characteristics of the impurity cations, and the character of the effect of γ-radiation on the spectral luminescence properties of impure crystals is analyzed (preliminarily). Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 64, No. 1, pp. 55–60, January–February, 1997.     

Theoretical analysis and simulation of conjugate heights for dual-conjugate AO system in lidar

A multi-conjugate adaptive optics （MCAO） can offer a possibility of widening field of view （FOV） characterized by the isoplanatic angle, and the choose of conjugate height becomes a basic problem for MCAO, which influences the size of iosplanatic angle. Considering the application of lidar, the isoplanatic angle＇s expressions of two deformable mirrors （DMs） MCAO for uplink and downlink are deduced. The effects of conjugate heights for dual-conjugate AO are thoughtfully discussed, and the isoplanatic angles are further analyzed. The results show that the isopanatic angle varies with the conjugate height and reaches the maximum as the conjugate height is at the optimal altitude. Moreover, the optimal conjugate height changes with the propagation distance.     

Quick single-photon detector with many avalanche photo diodes working on the time division

Due to the limit of response speed of the present single-photon detector, the code rate is still too low to come into practical use for the present quantum key distribution (QKD) system.A new idea is put up to design a quick single-photon detector.This quick single-photon detector is composed of a multi-port optic-fiber splitter and many avalanche photo diodes (APDs).Au of the ports with APDs work on the time division and cooperate with a logic discriminating and deciding unit driven by the clock signal.The operation frequency lies on the number N of ports, and can reach N times of the conventional single-photon detector.The single-photon prompt detection can come true for high repetition-rate pulses.The applying of this detector will largely raise the code rate of the QKD, and boost the commercial use.     

Sorting of bending magnets for the SSRF booster

The Shanghai Synchrotron Radiation Facility(SSRF)booster ring,a full energy injector for the storage ring,is deigned to accelerate the electron beam energy from 150MeV to 3.5GeV that demands high extraction efficiency at the extraction energy with low beam loss rate when electrons are ramping.Closed orbit distortion(COD)caused by bending magnet field uniformity errors which affects the machine performance harmfully could be effectively reduced by bending magnet location sorting.Considering the affections of random errors in measurement,both ideal sorting and realistic sorting are studied based on measured bending magnet field uniformity errors and one reasonable combination of bending magnets which can reduce the horizontal COD by a factor of 5is given as the final installation sequence of the booster bending magnets in this paper.     

Improvement of four-wave mixing-based wavelength conversion efficiency in dispersion shifted fiber by 40-GHz clock pumping

40-GHz clock modulated signal as a pump to improve the efficiency of four-wave mixing (FWM)-based wavelength conversion in a 26.5-km dispersion shifted fiber (DSF) is investigated. The experimental results demonstrate that the conjugated FWM component has higher intensity with the clock pumping than that with the continuous-wave (CW) light pumping. The improvement of FWM-based wavelength conversion efficiency is negligible when the pump power is less than Brillouin threshold. But when the pump power is greater than Brillouin threshold, the improvement becomes significant and increases with the increment of pump power. The improvement can increase up to 9 dB if pump power reaches 17 dBm.     

Characterization of PolyA and PolyC mismatches by Raman spectroscopy

A.C mismatches are studied by Raman spectral characterization of PolyA, PolyC, and their equimolar complex in solution of 0.14 mol/L Na ,pH7.0.Experimental results show that A·C mismatches occur to be A/B (mainly A) conformers, and unlike Watson-Crick base pairing, this kind of mismatches is stabilized by only one hydrogen bond involving cytosine N4H2 and adenine N7.The formation of A·C complex makes the base stacking interactions much stronger, and conformation of the backbone more ordered, which leads to obvious Raman hypochromic effect with some shifts in corresponding bands.