国际热核聚变反应堆馈线系统线圈终端盒冷屏热性能分析及实验研究

线圈终端盒是保证国际热核聚变实验堆装置可靠运行的关键部件之一,为磁体系统与低温车间、电源大厅、数据采集系统和低温控制元件提供4.5K的超低温工作环境。线圈终端盒内设有80K冷屏,以吸收室温环境对其内部工作空间带来的辐射热负荷。本文首先根据传热学原理对线圈终端盒冷屏热性能进行理论分析,确定了冷屏的结构型式,然后再对线圈终端盒冷屏结构建模,利用有限元流固体耦合分析软件FLUENT进行了数值模拟仿真分析,最后以设计分析结果为依据制作1∶1线圈终端盒整体实验系统进行实验验证,并对实验数据和数值模拟结果进行了分析比较,结果非常吻合,为下一轮冷屏结构的设计及大规模生产提供了可靠的依据。     

Shielding Effectiveness Measurements for Ferromagnetic Shields

This paper proposes a new way to measure the shielding effectiveness of ferromagnetic shields. The procedure combines an experimental characterization of the shielding material and numerical simulations. In a first case, magnetic hysteresis is reduced to a series of equivalent $B$ –$H$ linear relations through an optimization procedure that is applied to a measured set of symmetric minor loops, and an equivalent multilayer linear medium is defined through a subsequent iterative procedure. In a second case, magnetic hysteresis is reduced to a simple $B$–$H$ nonlinear relation, obtaining an equivalent nonlinear shield. In both cases, the obtained results are compared with the direct measurements of the shielding effectiveness at different operating frequencies, showing good agreement and the validity of the proposed method. A comparison and a discussion on the harmonic content of the attenuated field for the investigated shield geometry are reported. The same analysis is carried out for a basic diffusion problem, comparing the results with those obtained by the use of a Preisach model.      

Shielding design of the ITER NBI duct for nuclear and bremsstrahlung radiation

Three-dimensional Monte Carlo shielding analyses are conducted on the ITER Neutral Beam Injection (NBI) duct for the nuclear and bremsstrahlung radiation. The detailed distribution is evaluated about the nuclear heating rate and surface heat load of the NBI duct wall by the neutron and photon transport calculation. The analytical representations of these nuclear responses are established as a function of the distance from the blanket surface. It is clarified that these representations are different between the duct wall facing the plasma and that hidden from the plasma, and also between the duct wall in the blanket region and that in the vacuum vessel region. These results are very useful for the shielding design of the NBI duct wall in the nuclear fusion reactor.     

导电导磁屏蔽复合材料的研究进展

在查阅大量有关电磁屏蔽材料文献的基础上给出了导电导磁屏蔽材料的概念和内涵,分析了军民内外对该电磁屏蔽材料的需求原因,指出了当前屏蔽材料存在的问题并结合导电型屏蔽材料、导磁型屏蔽材料和导电导磁型屏蔽材料分析了当前电磁屏蔽材料的研究现状,最后结合作者自身研究提出了基于网络状导电导磁屏蔽复合材料的微结构设计方案并分析了其可行性.     

磁屏蔽效能的有限元分析

提出了磁屏蔽效能问题的三维有限元模型的建立方法,应用ANSYS软件得到磁屏蔽效能为28.78,并将结果绘制成曲线,使结果更加一目了然。为了检验计算结果是否符合实际情况,通过一种间接的方法对磁屏蔽效能进行测试。对比分析以上的计算结果和测试结果,可以得出结论:利用有限元法进行磁屏蔽效能计算,对直流传感器的磁屏蔽效能估算具有一定的指导意义。     

气隙对电流比较仪磁屏蔽屏蔽效能影响的研究

电流比较仪的磁屏蔽是减小磁性误差,提高测量精度的重要组成部分,但实际中磁屏蔽往往存在气隙导致屏蔽效能下降,影响比较仪的测量精度。通过建立有限元模型,研究磁屏蔽上引线穿出气隙对屏蔽效能的影响,得到了屏蔽效能随气隙高度变化的规律。对于该模型,气隙高度小于10 mm时,屏蔽效能下降不大;当气隙高度大于10 mm后,屏蔽效能下降明显。最后,搭建实验平台验证气隙对屏蔽效能的影响,实验结果与有限元计算结果相吻合,小气隙对屏蔽效能的影响不大,当气隙超过一定高度后对屏蔽效能影响很大,实际设计中应予以避免。     

电磁屏蔽材料的研究进展

简单介绍了电磁辐射的危害性及发展电磁屏蔽材料的意义,阐述了电磁屏蔽材料的屏蔽原理,较为详细地介绍了表层导电型、填充复合型、导电纤维、导电织物等电磁屏蔽材料及各种材料在工艺上的优缺点;同时阐述了各种电磁屏蔽材料的研究进展和发展前景,预测了电磁屏蔽材料的发展方向.     

Shielding of proton accelerators

This paper discusses some of the methods that can be employed for calculating shielding of proton accelerators, showing that a simple analytical model is often useful for a first estimate before going into complex Monte Carlo simulations. In particular what we call the Monte Carlo 'hybrid' approach, which employs source terms and attenuation length data calculated by Monte Carlo simulations under generic geometrical conditions, with a point-source line-of-sight model is discussed. Examples are given of the application of this method to the shielding calculations of two versions of the CERN SPL (2- and 3.5-GeV energy), comparing its results with Monte Carlo simulations of the full geometry.     

Experimental Investigation of the Magnetic Shielding Effect of Mineral Powders in a Drilling Fluid

Magnetic contamination of the drilling fluid shields the Earth's magnetic field measured by the magnetic sensors, and may contribute significantly to errors in directional surveying of a wellbore. A series of laboratory measurements were performed to investigate such magnetic shielding effects. In the measurement, a single axis fluxgate magnetometer was immersed in model drilling fluids prepared by mixing powders of known magnetic properties (magnetite and pure iron) into a solution of xanthan gum in fresh water, whereafter the vertical component of the Earth's field inside the fluid was measured. It was found that the strong shielding effect of dry iron powder essentially vanished when was suspended in the drilling fluid. The magnetic shielding caused by magnetite, however, remained significant also in solution, showing a complex dynamical behaviour. Initially the magnetic field was significantly damped, and this shielding was found to increase further for the next hour or so, reaching a fairly sharp maximum. The shielding then started to decay slowly and irregularly again over the next few days.     

电磁屏蔽复合材料的屏蔽性能预测

建立了填充椭球颗粒电磁屏蔽复合材料等效电磁参数的物理模型,基于变分原理和电磁波传输理论推导出其电磁屏蔽性能的预测公式,计算了不同填充条件下复合材料的屏蔽效能及反射率,分析了填料显微结构特征(浓度、形状、尺寸、分布方式)对复合材料屏蔽性能的影响规律.结果表明,复合材料屏蔽效能和反射率随填料填充浓度、长径比的增加而增大;针形和片形填料优于球形填料且定向分布好于随机分布;材料的反射率在特定的填充浓度及填料尺寸下存在峰值。屏蔽效能的计算结果与实验上填充球形银包羰基铁和镀镍短碳纤维的屏蔽复合材料的测试数据拟合较好。     

烘烤工况下的ITER中子屏蔽块整体结构分析

中子屏蔽块分布于国际热核聚变实验堆(ITER)超导托卡马克真空室双层壳体内部,由多个组件装配而成,用于屏蔽核聚变产生的中子。在烘烤工况下,承受螺栓预紧力作用的中子屏蔽块受200℃烘烤温度的影响,产生热应力。为校核在烘烤温度下中子屏蔽块的应力强度,本文采用ANSYS软件对其整个装配体进行整体结构分析。分析中将螺栓预紧力导致的模型位移作为边界条件,分预紧力载荷、温度载荷、重力载荷等载荷步进行热-结构耦合分析,分析结果按照ASME评定标准可以表明,中子屏蔽块各组件的最大应力强度在许用应力之内,满足结构强度要求。该分析的类型是典型的多接触高度非线性分析,对模型网格化和接触对设置的质量要求较高,处理不当会导致分析计算不收敛,同时该分析能正确地反映各结构件之间的实际连接关系,避免零件单独分析时用刚性连接代替弹性连接的状况。该分析方法为承受预紧力的复杂模型进行接触和耦合分析提供参考。     

基于超导磁场环境真空测量电离规磁屏蔽结构仿真研究

聚变装置超导磁场环境下真空测量电离规因灯丝变形、带电粒子轨迹变化等物理机制导致真空测量精度不高,不能满足工程精确测量的需求.基于磁屏蔽的理论,构建了半封闭式和开放式的两种多层磁屏蔽结构模型,利用Maxwell有限元软件,仿真研究了结构材料层不同厚度和不同磁场方向等条件下磁屏蔽效能的变化规律.结果 表明,屏蔽效能随铁层材...     

Optimization of Geomagnetic Shielding for MKIDs Mounted on a Rotating Cryostat

Superconducting detectors, such as microwave kinetic inductance detectors (MKIDs), are sensitive to the effects of ambient magnetic fields. There are two effects magnetic fields have on the response of MKIDs; the trapping of magnetic fields inside the superconducting materials degrades the resonator quality, and the time variation of the magnetic fields results in a baseline fluctuation. In the case of radio astronomy, this means the detector must be protected from the geomagnetic field. Here, we construct a test system to evaluate the effects described. We also evaluate the impact of the magnetic shield. We find that a shielding power of 47 dB is necessary in the case of application with a noise equivalent power of \(2.4 \times 10^{-16}\,\text {W}/\sqrt{\text {Hz}}\). We also confirm that the measured shielding power obtained using permalloy films is consistent with simulations based on the finite element method to an accuracy of 1 dB. We have designed magnetic shields for the GroundBIRD CMB telescope using these results. We achieve a sufficient shielding power of 55 dB.     

Chaotic signal generation in low-voltage vircator with electron source shielded from external magnetic field

The effect of shielding an electron source from a homogeneous external magnetic field of the drift chamber on the nonlinear dynamics of the electron beam with a virtual cathode (VC) and on the characteristics of output microwave radiation in a low-voltage vircator have been numerically simulated within the framework of a two-dimensional model. It is established that the increased degree of shielding of the electron source from the external magnetic field leads to the complication of the VC dynamics in the system and the corresponding chaotization of the output microwave radiation. Physical processes that account for the observed effect of shielding are analyzed.     

层压包装材料电磁屏蔽度模型研究

根据平面波屏蔽理论,从单层介质电磁屏蔽度模型出发,分析了多层层压包装材料的屏蔽特性,导出了其电磁屏蔽度模型。     

Improvement of YBCO Superconductor Magnetic Shielding by Using Multiple Bulks

HTS bulks present a high critical current density which can be used as magnetic shields. Previous works showed that BSCCO bulks can screen magnetic fields up to 0.1 T. For large scale applications like electrical machines, stronger magnetic field is usually needed. In so doing, (RE)BCO materials are more suitable since they can shield much higher magnetic fields. Another key issue concerns the size of the bulks. Nowadays, it is possible to manufacture 150-mm diameter class cylindrical YBCO bulk. In order to get larger magnetic shielding areas, multiple bulk superconductors should be arrayed and stacked in layers. This paper presents experimental results on screening performances of layered YBCO pellets. These results are compared with 2D simulations. The experiments are carried out at 77 K under external magnetic fields of 150 mT. Different topologies are considered: single-layer configuration with 9 square pellets and double-layer configuration with respectively 9 and 4 square pellets. Experimental and simulation results show that a checkerboard of one layer configuration does not fully shield the external magnetic field. Improved shielding properties are obtained when the double-layer configuration is used.     

Shielding design for the PANDA spectrometer at the Munich high-flux reactor FRM-II

The start-up of the Munich high-flux reactor FRM-II is in progress on. At the beam tube SR-2 the spectrometer PANDA has been installed. It is at three-axis neutron spectrometer looking onto a slightly under-moderated cold neutron source. For polarisation analysis, PANDA is equipped with a vertical cryomagnet producing fields up to 14.5 T for the sample. To get an appropriate shielding of the high-intensity instrument, one has to take into account the large cross section of the primary beam, several restrictions using magnetic materials, limitations in loading the site and finally, has to keep the lateral extent of the shielding small to allow for high-scattering angles. The shielding has been designed on the basis of the results, which were achieved by the combined use of both the Monte Carlo code MCNP-4B2 and an analytical method based on one-dimensional dose transmission functions.     

BEM calculation for magnetic shielding with steel sheets

The Boundary Element Method (BEM) is adapted to the solution of two-dimensional and axisymmetrical nonlinear shielding problems. The high vector-field accuracy attainable permits studies of extremely uniform nuclear magnetic resonance (NMR) fields to be made as well as less demanding shielding calculations. A technique is described in which nonlinearities are replaced by virtual sources in an explicit iteration scheme. All unknowns are on boundaries only and matrix size is not increased due to interior nonlinearities. An example is given. Suggestions for efficiency improvements are made.     

电磁搅拌法制备导电聚苯胺纳米线的电磁屏蔽性能研究

针对低频频段(<1.5GHz)的电磁屏蔽涂层,采用快速混合法制备出导电聚苯胺纳米线,使用透射电镜(TEM)对其形貌和尺度进行表征,研究了搅拌方式对聚苯胺/聚氨酯涂层的导电性能和电磁屏蔽性能的影响。研究表明,由于磁场的作用,采用电磁搅拌法可以缩短聚苯胺聚合反应时间,合成均一的导电聚苯胺纳米线,其渗滤阈值为33.3%,含量为33.3%的聚苯胺纳米线的聚苯胺/聚氨酯涂层的电磁屏蔽性能为32.2dB,优于含量为45%的机械搅拌法制备的聚苯胺粉体,这可能是由于线性结构的导电聚苯胺在基体中能够较容易形成三维导电网络结构所致。     

An accurate method of calculating multilayer, multimaterial cylindrical magnetic shields

The basic concepts of shielding theory have existed since the last century [1,2]. There have been many publications on the subject of magnetic shielding, treating the case of shielding apparatus from static fields by means of multiple concentric shields and deriving several principles of fundamental importance. Unfortunately, however, theory has been applied to only the most ideal shield configurations, for the case of constant permeability [3-5]. This paper covers the analysis of shielding effectiveness of variable Permeability cylindrical shielded enclosures for the DC magnetic field case. When the permeability is a function of magnetic induction, the simple boundary solution for spherical or cylindrical shields can no longer be applied since the induction, through the permeability, is caused to vary as much as two orders of magnitude, causing nonuniformity in the field in the cavity and inside the shield. Thus, the permeability of the shielding material is considered as a function of the induction, and a significantly improved method of estimating the induction and permeability of the shield is presented. The effects of a multiple-shell geometry are treated in the equations of this analysis. This method gives fast, accurate results and can be run on a small computer for shielding optimization. Results of these magnetic field calculations allowed the selection of optimization criteria and showed how system requirements could be met by choosing a suitable shell structure arrangement. Experimental measurements on real materials for various shell structures confirmed the accuracy of this method.