烧结钕铁硼磁体磁通不可逆损失的检测

磁通不可逆损失是永磁电机用烧结钕铁硼磁体的一个重要性能指标,其测量结果的准确性直接影响着电机的设计和磁体性能的选择.对比研究了不同测试条件下磁体的磁通不可逆损失.结果表明:磁通不可逆损失的测量结果主要受托盘性质(材质/规格)、磁体摆放间距和烘烤温度等因素的影响,为了获得准确的磁通不可逆损失测量结果,测量过程中应对这些因...     

Wiggler improvement based on single axis magnetic measurement, synthesized 3-D field simulation of trajectories and sorting of lateral focusing magnets

A method is presented for correcting magnetic field imperfections in an assembled wiggler of the Halbach configuration. The method is employed in a configuration in which lateral focusing is needed along the wiggler (at low beam energies and large length) and is provided by external magnet bars alongside the wiggler. Field deviations in both vertical and lateral dimensions due to wiggler imperfections are repaired by sorting and reassembly of the focusing magnets. A single Hall probe measurement along the wiggler axis and individual measurements of the focusing magnet bars provide sufficient data for sorting and optimal choice of the positions of the focusing magnets. Moreover, this data enables 3D simulation of the e-beam transport trajectories in the virtually synthesized field of the wiggler with the contemplated repair configuration of the focusing magnet bars before actually assembling them. It thus provides in advance a realistic prediction of the quality of the repair.     

A PC-based real-time Hall probe automatic measurement system formagnetic fields [of SRRC magnets]

A real-time, Hall-probe automatic measurement system was developed at the Synchrotron Radiation Research Center (SRRC) for the magnetic field measurement of the “C”-type rectangular combined function bending magnet, multipole magnets, and the insertion device magnets. The sampling rate on the x-y-z table with dynamic moving speed of 15 cm/s can be up to 200 samples/s, and the precision is within ±0.01%. A PC is used as a system controller which connects instrument function cards with instruments via the PC bus and an IEEE-488 interface card. An inexpensive, stable within ±15 ppm current source is produced to supply a high-stability constant current for the Hall probe; a temperature controller maintains the Hall probe temperature within ±0.2°C. The system's software has been divided into different modules that can be connected into a network global data base. System testing has shown that the magnetic field measurement accuracy of this system is better than ±25 ppm in the static measurement     

Application of the finite element method to the design of permanent magnets

A new method of determining the lengths of magnets in a magnetic circuit by using the finite element method has been developed. This method has the advantage that the lengths of magnets which produce the prescribed flux distribution can be directly calculated. In this paper, the error of this method is discussed at first, and then an example of application determining the shape of a magnet is shown. This method is effective for the design of magnetic circuits consisting of several permanent magnets and the determination of the shapes of magnets.     

Measurement of magnetization curves and losses in superconducting magnets at pulse durations of ≈ 1s

Wilson's method, which is commonly used for magnetization and loss measurement of superconducting magnets, has been thoroughly analysed with regard to its use with current pulses lasting ≈ 1 s. The factors substantially affecting the error of loss measurement have been revealed and ways of depressing their influence have been found theoretically and demonstrated experimentally. The errors, introduced by digital recording and processing have also been analysed. According to the results of this investigation, the total error in loss measurement can be lowered to a few per cent.     

Effect of Magnetic Field on Stability of Jet Motion in Electrospinning

Electrospinning uses an electrical charge to draw fine polymer fibers from a liquid. Stable jet stage and whipping instability stage exist in the electrospinning process. It is difficult to control stability of jet motion. Electrospinning with NbFeB permanent magnets is proposed to enhance the stability of jet motion in this paper. This method is very simple and effective. The electrospinning process assisted by magnets was observed by a high-speed camera, and the magnetic field was numerically analyzed by finite element method. The experimental results showed that the stability of jet motion increased obviously. We have explained that the magnets restricted and focused the motion of charges as a magnetic lens and created a uniform electric field distribution as an auxiliary electrode at the end of spinneret. The stable jet length, whipping instability cone angle, and fiber diameter were measured by experiments. The stable jet length increased significantly, the whipping instability cone angle decreased, and the average diameter of fibers increased slightly and distributed more evenly as the magnets were fixed at the end of spinneret.     

Energy calculation of a permanent magnet system by surface and fluxintegrals (the flux-mmf method)

Formulas are derived for the total magnetic energy of a system with no currents, linear soft magnetic materials, and linear permanent magnets that satisfy a zero curl condition involving their magnetization vector (zero equivalent volume current density). This class of magnets includes common parallel and radially magnetized NdFeB and ferrite magnets above the knee in their demagnetization curves. The formulas express the energy as a constant plus either an integral over the magnet surface of the magnetic vector potential or an integral through the magnet of the magnetic flux. The formulas provide theoretical foundation for the flux-magnetomotive force (mmf) method for calculating cogging torque of permanent magnet motors     

Heat transfer performance of cryogenic oscillating heat pipes for effective cooling of superconducting magnets

The cryogenic oscillating heat pipe (OHP) for conduction cooling of superconducting magnets was developed and the function was demonstrated successfully. OHP is a highly-efficient heat transfer device using oscillating flow of two-phase mixture. The working fluids that are employed in the present research are Nitrogen, Neon and Hydrogen, and the operating temperatures are 67–91 K, 26–34 K and 17–27 K, respectively. The estimated effective thermal conductivities from the measurement data of the OHP were higher than one of the solids such as copper at low temperature. These results revealed that the cryogenic OHP can enhance the performance of cooling system for magnets.     

Minimum-volume coil arrangements for generation of uniform magnetic fields

This paper describes an optimization method for designing electromagnetic coil arrangements that generate uniform magnetic fields. The method can accurately and efficiently determine an arrangement that minimizes the volume of the coils. An important advantage of the method is that the solutions it generates are guaranteed to be global minimums. The method may be useful for designing large superconducting magnets, since their cost depends strongly on the amount of superconducting wire required. It is also shown that the method can be applied to minimize the power consumption of resistive magnets.     

Calculating the external magnetic field from permanent magnets in permanent-magnet motors-an alternative method

We present an alternative method for calculating the magnetic field from a set of permanent magnets in a permanent-magnet motor. The method uses a cylindrical coordinate system to model the geometry of the structure enclosing the magnets. A Fourier series expansion yields an alternative to the more familiar multipole expansion given in spherical coordinates. The expansion is developed by using Green's function in cylindrical coordinates. A technique called charge simulation allows computation of an equivalent point charge distribution. Finally, Coulomb's law is applied to express the magnetic scalar potential in a mathematically tractable form.     

粘结Ni52Mn24.4Ga23.6磁体研究

真空感应熔炼法制备了多晶Ni52Mn24.4Ga23.6合金,对多晶合金进行了DSC分析和显微组织观察;采用粉末压缩压制的方法制备了粘结Ni52Mn24.4Ga23.6磁体;通过X射线衍射分析,讨论了外应力场和磁场对粘结Ni52Mn24.4Ga23.6磁体马氏体相变的影响;测量了粘结Ni52Mn24.4Ga23.6磁体在磁场下的磁诱发应变.结果表明:室温时粘结磁体在1.2T的磁场下能产生150ppm的饱和伸长应变.     

Biaxial testing of high strength carbon fiber composite cylinders for pulsed magnet reinforcement

A methodology is introduced to test carbon-fiber-reinforced, hoop-wound composite cylinders for their biaxial mechanical properties under axial compression and hoop tension. The understanding of the behavior of these composites under biaxial loads is extremely important in the design of pulsed magnets. These composites are used as reinforcements for both the inner conducting layers and as an overall exterior reinforcement. Testing of actual pulsed magnets to ascertain design change effects of composite reinforcement schemes on the maximum attainable field can be expensive; hence, a standard biaxial testing method is desirable which is relevant to the design of pulsed magnets. In this investigation, an attempt was made to produce a standard testing procedure aimed at measuring the biaxial mechanical properties (elastic, plastic, and failure envelope) of composite materials. This methodology was applied to two different carbon/epoxy based composites. The results of these tests (elastic properties and failure points) are compared with theoretical predictions, specifically those due to Tsai-Wu.     

Measurements of thermal conductivity of epoxy impregnated NbTi andNb3Sn windings

The effective thermal conductivity in the transverse direction is one of the less predictable coil parameters. In the framework of the construction of a high-field solenoid (18 T, 100 mm free bore at 4.2 K) at the LASA lab, an experimental apparatus was built for measurement of thermal conductivity of pure materials as well as of composites and coil blocks. The main aim of the experiment is the measurement of the thermal conductance of pieces of real NbTi and Nb₃Sn windings. The authors discuss how the thermal conductivity affects the quench properties of superconducting magnets. The main features of the experimental apparatus are described together with a calculation and a measurement of the thermal loss. Preliminary measurements on some pure materials as well as on a coil block are presented     

掺杂Dy_2O_3Nd－Fe－B磁体的氧含量对磁性能的影响

用穆斯堡尔效应和磁性测量等方法，研究了掺杂Ｄｙ_２Ｏ_３Ｎｄ－Ｆｅ－Ｂ磁体的氧含量对磁性能的影响以及氧含量与掺杂浓度和制粉球磨时间的关系，结果表明，掺杂Ｄｙ_２Ｏ_３可以有效地提高磁体的矫顽力，但其剩磁和最大磁能积会不同程度地降低，磁体中的氧含量由掺杂浓度和制备工艺所决定，并满足一定关系式。当掺杂浓度为１．０ｗｔ％时，磁性能在氧含量为１１０００ＰＰｍ附近发生突变。     

Force and Stiffness of Passive Magnetic Bearings Using Permanent Magnets. Part 2: Radial Magnetization

This paper deals with the calculation of the force and the stiffness between two ring permanent magnets whose polarization is radial. Such a configuration corresponds to a passive magnetic bearing. The magnetic force exerted between ring permanent magnets is determined by using the Coulombian model. The expressions obtained are semianalytical and we show that it is not possible to find an exact analytical expression of the force between two ring permanent magnets. Then, thanks to these semianalytical calculations, the ring dimensions are optimized in order to have a great force or a great stiffness. Moreover, we show that the relative position of the rings for which the force is the strongest depends on the air gap dimension. This result is new because the curvature effect is taken into account in this paper. We can say that such semianalytical expressions are more precise than the numerical evaluation of the magnetic forces obtained with the finite-element method. Moreover, semianalytical expressions have a low computational cost whereas the finite-element method has a high one. Thereby, as shown in this paper, such calculations allow an easy optimization of quadripolar lenses or devices using permanent magnets.      

A Novel Method of Arraying Permanent Magnets Circumferentially to Generate a Rotation Magnetic Field

An outer magnetic field is extensively applied to drive the movement of a clinic micro-robot. However, how to produce a suitable magnetic field is a complicated problem. Commonly, the drive magnetic field is generated by a combination of power coils. This paper presents a novel method that circumferentially arrays identical permanent magnets to generate a rotational magnetic field in the center area of the array circle. First, we distribute permanent magnets uniformly in a circle, and adjust each of them at a corresponding initial angle. All of the magnets rotate in the same direction synchronously, generating a constant strength and reverse rotation magnetic field in the center area of the circle. The rotation speed of the generated magnetic field equals that of the permanent magnets. We used two models to analyze the magnetic field, and did some numerical analyses. We set up a test-bed and carried out some experiments to prove the feasibility of the novel method. The method seems to have wide applicability in designing magnets to drive micro-robots for diagnosis and treatment.      

大型氦低温系统中的杂质净化

EAST是一个全超导的托卡马克核聚变实验装置,磁体采用超临界氦迫流冷却.磁体在降温过程中对氦气的纯度有很高的要求,净化系统是整个低温系统的重要环节之一,以防各种杂质气体在低温下凝结固化威胁低温系统的稳定可靠运行.理论分析了氦气纯化的基本原理及固定床吸附器的吸附机理,对低温纯化器的运行进行了阐述,并介绍了杂质成分检测系统,以对净化效果进行评估,实验得知氦气净化系统能满足低温系统氦气高纯度的要求.     

Linear synchronous motor development for urban and rapid transit systems

The following paper presents and discusses technical variants in magnetic suspension-repelling permanent magnets, electrodynamic and electromagnetic suspension methods, controlled lift magnets. In addition, propulsion methods for magnetically suspended vehicles are also shown. The synchronous long stator linear motor has achieved particular importance since it makes possible an efficient energy conversion. The load-carrying capacity is not reduced by the weight of the drive and the layout enables a very good integration of the lift and thrust functions. A further reduction of the on-board power requirements can be achieved by using permanent magnets to generate the rated induction in the air gap. Several magnetic suspension systems constructed or under construction with the long stator method are also mentioned.     

退火处理对烧结Nd-Fe-B永磁体磁性能的影响

本文研究了Nd Fe B材料的低温退火处理,普通商品化生产的N35磁体在3Pa真空度、492℃条件下对普通钕铁硼退火处理1h,其矫顽力Hc和最大磁能积(BH)max值均有较大幅度的提高。