Effect of Mirror Magnetic Field on Abnormal Glow Discharge of Four-Anode Device

Abstract In the four-anode device, the mirror magnetic field affects the characteristics of charged particles motion, so that the current-voltage relations of glow discharge are changed. Firstly, the discharge device is introduced, and the distribution of mirror magnetic field generated by the loops surrounding the discharge chamber is presented. Both the discharge current-voltage characteristics and the radial distributions of electron density are measured, respectively, with/without the magnetic field. When the discharge occurs in a 99.99% helium with a pressure ranging from 100 Pa to 800 Pa without magnetic field, the voltage, sustaining a certain abnormal glow discharge current, decreases with the increase in gas pressure. With a mirror magnetic field of certain intensity, the discharge voltage increases with the current in a rate slower than that without the magnetic field. Moreover, when the magnetic field intensity increases, the discharge voltage first decreases then increases. Simultaneously, the mirror magnetic field affects the moving characteristics of charged particles, and causes a more inhomogeneous electron density.

Unconventional room-temperature negative magnetoresistance effect in Au/n-Ge:Sb/Au devices

Non-magnetic semiconductor materials and their devices have attracted wide attention since they are usually prone to exhibit large positive magnetoresistance(MR)effect in a low static magnetic field environment at room temperature.However,how to obtain a large room-temperature negative MR effect in them remains to be studied.In this paper,by designing an Au/n-Ge:Sb/Au device with metal electrodes located on identical side,we observe an obvious room-temperature negative MR effect in a specific 50 T pulsed high magnetic field direction environment,but not in a static low magnetic field environment.Through the analysis of the experimental measurement of the Hall effect results and bipolar transport theory,we propose that this unconventional negative MR effect is mainly related to the charge accumulation on the surface of the device under the modulation of the stronger Lorentz force provided by the pulsed high magnetic field.This theoretical analytical model is further confirmed by regulating the geometry size of the device.Our work sheds light on the development of novel magnetic sensing,magnetic logic and other devices based on non-magnetic semiconductors operating in pulsed high magnetic field environment.

THE OPTIMAL MAGNETIZING FIELD DISTRIBUTION FOR FERRITE DUAL-MODE DEVICES

The optimal magnetizing fields of the variable polarization effects of ferrite are studied by using thecoupling-wave(cw)theory,vaiational principle and optimization techniques.Several kinds of shapes of themagnetic line of force and some valuable results of the optimal magnetizing field are given.The theoretical cal-culations are in good agreement with the experimental results.

Magnetoelectric Multiferroic Composites： Phenomena and Devices

Detailed mathematical modelling approaches that are used to describe the dynamic behaviour of magnetoelectric coupling in magnetostrictive-piezoelectric multiferroics at low-frequencies, in electromechanical resonance region and at microwave range are discussed. The ME （magnetoelectric） voltage coefficients were estimated from the known material parameters. The feasibility for creating new class of functional devices based on magnetoelectric interactions is addressed.

Performance study of aluminum shielded room for ultra-low-field magnetic resonance imaging based on SQUID： Simulations and experiments

The aluminum shielded room has been an important part of ultra-low-field magnetic resonance imaging （ULF MRI） based on the superconducting quantum interference device （SQUID）. The shielded room is effective to attenuate the external radio-frequency field and keep the extremely sensitive detector, SQUID, working properly. A high-performance shielded room can increase the signal-to-noise ratio （SNR） and improve image quality. In this study, a circular coil with a diameter of 50 cm and a square coil with a side length of 2.0 m was used to simulate the magnetic fields from the nearby electric apparatuses and the distant environmental noise sources. The shielding effectivenesses （SE） of the shielded room with different thicknesses of aluminum sheets were calculated and simulated. A room using 6-mm-thick aluminum plates with a dimension of 1.5 m x 1.5 m x 2.0 m was then constructed. The SE was experimentally measured by using three-axis SQUID magnetometers, with tranisent magnetic field induced in the aluminum plates by the strong pre-polarization pulses. The results of the measured SE agreed with that from the simulation. In addition, the introduction of a 0.5-mm gap caused the obvious reduction of SE indicating the importance of door design. The nuclear magnetic resonance （NMR） signals of water at 5.9 kHz were measured in free space and in a shielded room, and the SNR was improved from 3 to 15. The simulation and experimental results will help us design an aluminum shielded room which satisfies the requirements for future ULF human brain imaging. Finally, the cancellation technique of the transient eddy current was tried, the simulation of the cancellation technique will lead us to finding an appropriate way to suppress the eddy current fields.

Magnetic field distribution simulation and performance experiment of a magnetic seed-metering device based on the combined magnetic system

The magnetic seed-metering method is one of the universal approaches for plug tray seeding.Conventional electromagnetic and permanent-magnetic seed-metering devices either cannot supply a desirable magnitude of magnetic force or need a seed-clearing mechanism.Thus the objective of this research was to develop a combined magnetic system(CMS)seed-metering device for generating higher magnetic forces than the electromagnetic ones without using any auxiliary seed-clearing mechanisms.Firstly,the CMS component was designed and its magnetic field distributions in both attractive and clearing states were obtained by finite element method simulations.Secondly,based on the CMS components,a magnetic seed-metering device was developed and validated by a prototype experiment.The simulation results displayed that along the axial direction of the magnetic head,the maximum magnetic flux density in the clearing state was 21.03%of that in the attractive state.In addition,along the radial direction,the proportion was 24.16%.Concerning the spatial magnetic flux density distribution,the magnetic flux density on the seeding planes of CMS components(approximately 60 mT)was higher than that of transitional space between two CMS components(nearly 0 mT).As for the seeding performance experiment,when the rotational speed of the roller was 21 r/min and the exciting current was 0.15 A,the highest single rate was acquired(90.20%).In the same condition,the reseeding rate was 5.88%and the miss-seeding rate was 3.92%.The results suggest that the magnetic field distribution and seeding performance of the developed magnetic seed-metering device are acceptable.Therefore,the developed magnetic seed-metering device can be used in practical plug tray seeding processes.

Magnetoresistance retraction behaviour of Ag/p-Ge:Ga/Ag device under pulsed high magnetic field

In non-magnetic semiconductor materials,unsaturated magnetoresistance(MR)effect has attracted lots of attention due to its physical interests and potential applications in electronic devices.Under the ex-tremely high magnetic field,the stability and reliability of MR effects based on the non-ohmic transport has been rarely researched.In this paper,the transport properties of non-magnetic Ag/p-Ge:Ga/Ag devices under 45 T pulsed high magnetic field at 300 K are investigated.It is found that in ohmic conduction re-gion(I<5 mA)where the single dominant carrier is hole,the MR values increase with increasing the applied magnetic field,presenting a conventional unsaturated behavior.In the two non-ohmic regions(5 mA≤I≤100 mA)where the transport is dominated by bipolar(electrons and holes),a MR retraction has been obviously observed under pulsed high magnetic field.Combining the Hall measurement results and calculation of Hall effect with bipolar-driven transport model,the mechanism of the MR retraction is analysed,in which the MR retraction may be related to the strong regulation of electron-to-hole den-sity ratio by pulsed high magnetic field.This work provides a reference for evaluating the stability and reliability of the properties of non-magnetic semiconductor based MR devices under the interference of strong magnetic pulses.

双磁场控制的磁流变减震结构振动台试验研究

传统磁流变减隔振器通常由线圈持续供电,不仅增大耗能,也会减少器件的使用寿命。基于磁流变凝胶(MRG)的剪切工作原理,运用剪切型结构设计一种新型磁流变凝胶减震装置,采用永磁体和线圈共同控制磁场大小和方向,通过改变磁流变凝胶的磁化程度实现阻尼力大小的控制。将该装置安装在一2层钢框架结构模型的底层,采用恒定电流控制法开展磁流变减震结构振动台试验研究,分析不同电流下减震结构系统对不同地震波的振动控制效果。试验结果表明:该磁流变凝胶减震装置能够显著降低结构的动力响应,对于不同的地震波其减震效果有所差异,随着峰值加速度的增加其减震效果有所下降。

50mT静磁场试验装置的研制和性能验证

为了满足有源植入式医疗器械标准中静磁场试验要求,研制了一款静磁场抗扰度试验装置。在输入电流约4.75 A条件下,该装置的磁通密度可以达到50 mT,且试验均匀域的磁通密度均匀性偏差达到2.8%。在0.055~50mT范围内,磁通密度的线性度达到了0.6%。该装置还可以实现对电压、电流、时间、温度以及电磁场曝露等参数进行有效地监控。该研究为有源植入式医疗器械的静磁场抗扰度试验提供了理论和技术支撑。

回旋加速器主磁铁镶条再加工工艺研究

回旋加速器主磁场测量与垫补是回旋加速器技术研究的一个重要方向。为实现回旋加速器主磁场垫补理论要求,其垫补方式可采用边缘垫补方式。该方式要求加工的镶条边缘曲线的精度优于0.02 mm。然而,镶条初次加工方式为配做形式,本身镶条材料硬度低、形状薄且长,在强磁场条件下,细微扰动就会引起磁场剧烈变化,实际需要进行垫补加工量非常小。故保证镶条边缘曲线再加工精度是实现回旋加速器功能非常重要的工作。文章从边缘理论曲线获得方式出发,提出加工精度具体要求和边缘曲线加工的实现方式,并考虑其坐标系关系,设计了一种保证镶条边缘曲线再加工精度的工装。该工装可同时固定两根镶条,提供合适的参考点,实现镶条在加速器上的位置复现。该工装应用于16 Mev加速器镶条垫补加工,每次垫补结果机械测量误差在0.02 mm,磁场复测后实际加工磁场与理论垫补磁场精度好于10-3。

激光等离子体实验中脉冲强磁场设备产生的电磁干扰和屏蔽方法

脉冲强磁场在高功率激光与物质相互作用领域有着重要的作用。报导了用于激光等离子体实验的脉冲强磁场设备产生的电磁干扰的空间和频谱分布特征以及屏蔽方法的实验结果。发现电磁干扰来自于脉冲强磁场设备的放电主回路、充电和接地的次级回路。这些电磁干扰主要通过电容性耦合进入真空靶室、进而通过传导型耦合途径从靶室进入电子设备,或通过充电线和接地线进入电网或弱电电缆、最终进入电子设备,部分电磁辐射通过自由空间传输方式耦合进电缆和电子设备。通过断开传导型耦合路径和屏蔽自由空间电磁辐射等途径来消弱电磁干扰,对比实验发现这些措施对抑制电磁干扰有明显的效果。这些结果可以应用于强磁场调控激光等离子体的实验研究。

Magnetostrictive composite material-based polarimetric heterodyning fiber-grating laser miniature magnetic field sensor

A novel fiber-optic magnetic field sensor is demonstrated based on a dual-polarization fiber-grating laser, which is embedded in an epoxy resin-bonded magnetostrictive composite material with doped Terfenol-D particles. A simple structure is designed to convert the magnetic field-induced strain to transversal stress, which is applied to the fiber laser to produce beat note frequency changes for measurement purposes. The response of the proposed sensor is measured, and shows quite a good directivity and linearity with a sensitivity of 10.5 Hz/μT to the magnetic field. It also shows a large measurable range up to about 0.3 T.

永磁交变磁场磁粒研磨装置及试验研究

为改善平面磁粒研磨加工的效果,增强磁场的变化,使磨料进行翻滚更新。本文设计一种永磁交变磁场磁粒研磨装置,此装置采用了永磁交变磁极产生的交变磁场进行磁粒研磨加工。利用软件对永磁交变磁场进行模拟仿真,并观察研磨区域磁感应强度的变化。在研磨试验中,用SUS304不锈钢板件作为试验件,研磨时间为30 min,磁性磨料粒径为80目,主轴转速分别为150 r/min、200 r/min、250 r/min。使用超景深显微镜与触针式粗糙度测量仪对工件加工前后的表面形貌与粗糙度进行检测。通过对比可得,SUS304不锈钢板的表面形貌逐渐改善,纹理和凹坑基本去除;表面粗糙度由原始的0.329μm降至0.069μm,达到了光整加工的效果。采用永磁交变磁场磁粒研磨装置可以加快磁性磨粒的更新,使研磨轨迹更加复杂化,从而提升研磨效果,提高研磨效率。

磁流变惯容器设计与性能分析

为了提高传统磁流变阻尼器在低频域的减振性能,提出了一种新型磁流变惯容器,包括变阻尼单元和惯容单元两部分,由磁流变阀、液压马达与飞轮等组成。利用活塞杆与缸筒的相对运动,实现变阻尼单元内的磁流变液在磁流变阀内往复流动,通过调控线圈上电流大小改变输出阻尼的大小;同时,实现油液推动液压马达输出轴及飞轮转动,输出器件的惯容特性。为提高磁流变阀内置通道的磁场利用率,提出了磁路设计优化方法,采用有限元方法对磁流变阀内部磁场强度进行仿真。结合磁场仿真与理论分析,设计并试制了样机,搭建了器件性能平台进行测试。结果表明,所设计器件能够表现出惯容特性,具有良好的阻尼可控性。

核聚变堆极向场线圈氦冷却管结构设计与优化

【目的】氦冷却管是聚变超导磁体系统的核心部件,承担着超导磁体冷却通道与低温系统的连接,直接关系着超导磁体系统的运行稳定。由于氦冷却管需在装置现场进行焊接,因此氦管结构设计需从功能实现和现场工艺可操作性等多角度综合考虑,提出合理解决方案。【方法】通过综合分析聚变堆极向场结构,开展了低温氦冷却管结构优化及压损评估研究,并从结构力学角度对氦孔尺寸和焊缝倒角优化设计方面进行了全面的对比分析,提出聚变堆磁体氦冷却管设计准则一般要求。结合氦冷却管结构力学分析、压损分析,并综合考虑现场可操作性,提出氦冷却管设计方案,以满足聚变堆磁体氦冷却管要求。【结果】短跑道氦冷却管虽然会导致局部压损增大,局部压损相当于2.7 m长的导体,但与线圈总长相比,其所带来的压损基本可忽略。【结论】采用短跑道型氦管设计方案不仅可以满足功能需求,还可极大提高现场工艺可操作性,可满足聚变堆超导磁体氦冷却管要求。

CAT-1超导磁悬浮系统的平衡分析与永磁实验装置设计

天环一号(CAT-1)是国内首个采用磁悬浮偶极场磁体设计的磁约束等离子体装置。本文根据CAT-1装置总体目标和参数设计要求,采用线电流简化模型,基于矢量磁场、力学平衡及动力学等方法,完成了超导磁悬浮系统的平衡稳定分析,给出了参数设计结果;初步设计出简化的永磁悬浮实验装置,用于检验超导磁悬浮系统稳定性及参数可靠性。结果表明:对于CAT-1装置的悬浮磁体1200 kg、电流5 MA、悬浮距离2.0 m设计目标,托举线圈半径最优值为1.7 m,相应的电流为3.49 kA,为实现对悬浮磁体偏移运动的有效阻减及控制,平衡点附近工作区域应限制在垂直位移Δz<0.1 m、水平位移Δer<0.05 m、倾斜角位移Δα<π/24;分析了TSR线圈对悬浮线圈的影响,计算显示TSR与悬浮线圈产生对向漂移,漂移幅度与径向位置有关,同时TSR线圈侧原本闭合磁力线被破坏,造成输运粒子损失;采用1.5 kg永磁完成了悬浮实验装置概念设计,分析表明永磁体与托举线圈间距0.1 m,铜导托举线圈电流895 A,满足控制对响应速度的要求。

基于多参数变量优化的户内空心电抗器电磁屏蔽方案研究

为解决户内空心电抗器漏磁导致其周围电磁污染严重、金属设备发热问题,采用ANSYS有限元仿真平台,对500 kV变电站的户内空心电抗器及其周围附属设施和房屋结构进行三维电磁建模,并在房屋顶部加设屏蔽板。通过对屏蔽体的材料、厚度及缝隙宽度等多参数变量进行优化分析,形成了一个改善户内电抗器周边电磁环境的方案。仿真结果表明:在钢梁上方增设由3 mm厚的铝板重叠搭接成的屏蔽板,可以有效降低房屋钢结构的磁感应强度,运行时电抗器温度变化符合空心电抗器要求的绝缘耐热等级,屏蔽装置边缘断面温度较高,最高点为53.26℃,周围建筑设施平均温度约增加5~10℃,满足安全运行要求。

强流相对论环形电子束在低磁场中传输分析

用理论和粒子模拟相结合的方法分析了强流薄环形相对论电子束在低磁场导引下,在均匀波导,无箔二极管,以及锥形波导和渐减磁场位形条件下的传输过程,研究了束包络的波动和如何减少波动的问题。分析表明:在无箔二极管中一个适当渐增的磁场位形可以有效地抑制束电子的径向运动,从而减少电子在波导中的波动幅度;电子束在锥形波导和渐减磁场位形中运动,不会增加束电子的波动。因此适当的磁场位形可以降低微波器件对导引磁场的要求,有利于实现永磁包装微波器件。

爬壁机器人永磁吸附装置的优化设计

为满足水轮机叶片修复对爬壁机器人负载能力和运动灵活性的要求,设计了一种具有强吸附能力的永磁吸附装置。吸附装置吸附于水轮机叶片表面时,吸附装置和叶片表面之间有一定的气隙(非接触的),以减小爬壁机器人的运行阻力。非接触吸附装置由多个吸附单元组成,吸附单元之间按照一定方式进行耦合,吸附单元由永磁体和轭铁组成。运用有限元方法,建立吸附装置磁场数值计算模型,对吸附单元关键结构参数及吸附单元间耦合方式进行了分析和优化设计。实验结果表明,该吸附装置在气隙为6.2mm的情况下能提供2400N的吸附力,吸附装置自重小,吸附能力强,适用于曲率半径在1.5m以上的导磁壁面。

三维磁敏传感器的设计及误差分析

采用三维磁敏传感器有助于降低磁场测量系统的复杂性和提高磁场测量速度。介绍了基于霍尔元件的三维磁敏传感器的设计方法,分析了霍尔元件的粘贴角度偏差、传感器的体积对测量精度的影响,并对传感器的总体误差进行了估算,其分析结果对三维集成磁敏传感器的设计具有指导意义。