In situ calibration of rotating sensor coils for magnet testing

An in situ procedure for calibrating equivalent magnetic area and rotation radius of rotating coils is proposed for testing accelerator magnets shorter than the measuring coil. The procedure exploits measurements of magnetic field and mechanical displacement inside a reference quadrupole magnet. In a quadrupole field, an offset between the magnet and coil rotation axes gives rise to a dipole component in the field series expansion. The measurements of the focusing strength, the displacement, and the resulting dipole term allow the equivalent area and radius of the coil to be determined analytically. The procedure improves the accuracy of coils with large geometrical irregularities in the winding. This is essential for short magnets where the coil dimensions constrain the measurement accuracy. Experimental results on different coils measuring small-aperture permanent magnets are shown.     

Optimum spacing for a pair of thick circular coils of square section

Curves are given for the magnetic field along the axis between two circular coils of square section traversed by the same current. These curves relate the field variations, the length in which the field is within a certain allowed variation, the coil thicknesses, and their separation.     

Optimization of dimensions of a device for circular magnetization of cylindrical components. III. Investigation of circular field component generated by a one-layer toroidal coil

The effect of dimensions of a toroidal coil and the number of turns in the coil on the circular magnetic field component within the region limited by the inside axial sections of the turns has been studied. The configuration of this field has been determined. Optimal dimensions of the coil have been calculated. In order to obtain a higher amplitude of the circular field, one should use coils with smaller numbers of turns. In the inner region of a one-layer toroidal coil close to the turns, the peaks of the circular field diminish with the number of turns, but the number of points where the field intensity is maximal becomes larger, i.e., the field becomes more uniform. Methods of further increase in the circular component of the magnetic field have been suggested.     

Modeling and Configuration Design of Electromagnetic Actuation Coil for a Magnetically Controlled Microrobot

Non-contact actuated microbeads have attracted a lot of attention in recent years because of its enormous potential in medical, biological, and industrial applications. Researchers have proposed a multitude of electromagnetic actuation(EMA) systems consisting of a variety of coil pairs. However, a unified method to design and optimize a coil pair according to technical specifications still does not exist. Initially, this paper presented the modeling of an untethered ferromagnetic particle actuated by externally applied magnetic field. Based on the models, a simple method of designing and optimizing the EMA coil pair according to technical specifications, was proposed. A loop-shaped coil pair generating uniform magnetic and gradient fields was chosen to demonstrate this method clearly and practically. The results of the optimization showed that the best distance to radius ratio of a loop-shaped coil pair is 1.02 for a uniform magnetic field and 1.75 for a uniform gradient field. The applicability of the method to other shapes of coil configuration was also illustrated. The best width to distance ratio for a square-shaped coil pair is 0.558 and 0.958 for uniform magnetic and gradient fields, respectively. The best height to width ratio and distance to width ratio for a rectangle-shaped coil pair is h/w = [0.9,1.1], d/w = [0.5,0.6] for uniform magnetic field and h/w = [1.0,1.2], d/w = [0.9,1.1] for uniform gradient field. Furthermore, simulations of a microparticle tracking the targeted trajectory were conducted to analyze the performance of the newly designed coils. The simulations suggested the ability of manipulating microparticles via the coils designed by our proposed method. The research mainly proposed a unified design and optimization method for a coil pair, which can support researchers while designing a specific coil pair according to the technical requirements. This study is aimed at researchers who are interested in EMA system and microrobots.     

Note: design of a novel rotating magnetic field device

A novel device to produce a rotating magnetic field was designed, constructed, and tested. The system consists of a Helmholtz coil pair which is mechanically coupled to a dc electric motor whose angular velocity is controlled. The coil pair generates a uniform magnetic field; the whole system is rotated maintaining the coils energized using brushes. The magnetic field strength is uniform (≈5.8 mT) for a workspace of about 100 mm along the rotation axis. The system remains free of undesirable high amplitude mechanical vibrations for rotation frequencies below 10 Hz. We verified the performance of the apparatus by conducting experiments with magnetic swimmers.     

Design and fabrication of a superconducting magnet for an 18 GHz electron cyclotron resonance ion∕photon source NFRI-ECRIPS

A superconducting magnet was designed and fabricated for an 18 GHz ECR ion∕photon source, which will be installed at National Fusion Research Institute (NFRI) in South Korea. The magnetic system consists of a set of four superconducting coils for axial mirror field and 36 pieces of permanent magnets for hexapolar field. The superconducting coils with a cryocooler (1.5 W @ 4.2 K) allow one to reach peak mirror fields of 2.2 T in the injection and those of 1.5 T in the extraction regions on the source axis, and the resultant hexapolar field gives 1.35 T on the plasma chamber wall. The unbalanced magnetic force between the coils and surrounding yoke has been minimized to 16 ton by a coil arrangement and their electrical connection, and then was successfully suspended by 12 strong thermal insulating supports made of large numbers of carbon fibers. In order to block radiative thermal losses, multilayer thermal insulations are covered on the coil windings as well as 40-K aluminum thermal shield. Also new schemes of quench detection and safety system (coil divisions, quench detection coils, and heaters) were employed. For impregnation of the windings a special epoxy has been selected and treated to have a higher breaking strength and a higher thermal conductivity, which enables the superconductors to be uniformly and rapidly cooled down or heated during a quench.     

Coil design optimization for an induction evaporation process: Simulation and experiment

For the purpose of utilizing induction heating in the evaporation process, the effects of induction coil design and droplet size on induction heating efficiency are investigated. Electro-magnetic simulations with various induction coil designs were conducted to predict the electro-magnetic field distribution. The induction coils were fabricated in order to verify the simulation results under atmospheric evaporation test conditions. The electro-magnetic simulation results indicated that the magnetic field became widened around the Zn droplet when the size of the Zn droplet increased. This in turn attributed to the increase in induction heating energy efficiency. The energy efficiency of the induction coil with 4-windings was the highest among the 3-, 4-, and 5-windings induction coils. Energy efficiency tendencies derived by the atmospheric evaporation tests corresponded well to the simulation results, and maximum energy efficiency was measured to be 42% under the atmospheric evaporation tests.     

Magnetic pulser and sample holder for time- and spin-resolved photoemission spectroscopy on magnetic materials

A compact coil setup, in conjunction with a high power current pulser, is presented; developed especially for time- and spin-resolved photoemission spectroscopy measuring the sample in magnetic remanence at room temperature. A novel approach is presented where the sample is switched in the stray field of a coil pair. This enables the electrical biasing of the sample without altering the electron trajectories due to field gradients introduced by the coils. The pulser driving the coils reaches a peak power of 1 MW at 1 kA with a switching frequency up to 10 kHz suitable for experiments, for example, with state of the art repetition rates of femtosecond laser systems.     

A linear superconducting suspension for a gravity-inertial instrument

A noncontact stable linear suspension is proposed for a ring-shaped superconducting coil in the magnetic field of two other stationary ring-shaped superconducting coaxial coils. The suspended coil is located between the stationary coils. To measure the displacement of the suspended coil, the stationary coils are connected in parallel and a low-inductance measuring coil is placed in the circuit between the connection points. The current in the measuring coil varies according to a linear law as the suspended coil is displaced along the common axis of the stationary coils. The characteristics of the instrument based on such a suspension are numerically evaluated. Due to the absence of a displacement meter as a separate unit, it is possible to simplify the design of the instrument to the maximum extent and exclude the reverse effect of the displacement meter on the suspended coil.     

Mathematical model of a double-coil inductive transducer for measuring electrical conductivity

A technique for the contactless measurement of the electrical conductivity of conducting materials using a double-coil inductive transducer is presented. A mathematical model of the transducer has been created and it consists of two cylindrical coils and a tested sample in the form of a cylinder coaxial with the coils. A processing function of the transducer is defined as the ratio of voltages between terminals of the measurement coil with and without the test sample. This processing function depends on the conductivity of the test sample, the dimensions of the sample and of both coils of the transducer (the measurement coil and the excitation coil), and the frequency of the current supplied to the excitation coil. An analytical formula for the processing function is derived; analysis of graphs of this function in different formats enables us to evaluate the influence of all the essential parameters of the transducer. This is a necessary step for both transducer optimization and carrying out of the conductivity measurement of the investigated materials. In order to verify the theoretical predictions, experimental investigations have been performed using a computerized data acquisition system. First, an experimental validation of the obtained analytical formula has been completed using an aluminum sample of known conductivity. Then, the conductivity measurements of a sample made of brass have been carried out. The obtained experimental results confirm the high accuracy of the theoretical analysis.     

Optimization of dimensions of a device for circular magnetization of cylindrical components. IV. Investigation of circular magnetizing field generated by a multilayered toroidal coil

The effect of dimensions of a toroidal coil, the number of turns and layers in its winding on the circular field component generated in its inside volume defined by the inside axial sections of the turns has been investigated. The configuration of the field in this region has been calculated, and the principles of the design of magnetizing coils have been formulated. In order to obtain a higher circular field intensity in the region close to the turns, it is advisable to use multilayered windings. A fairly uniform circular field is generated in a local region if the winding is divided into equal sectors containing zones with turns of wire and gaps between them. In order to obtain a circular field component of a relatively high intensity and a constant sign over a wide sector of the inside volume, one should build a coil of several sections uniformly distributed over the frame perimeter.     

Improvement of the Uniformity of the RF Field Generated by the Helical Surface Coil of a Nuclear-Quadrupole-Resonance Spectrometer

A simple and rather efficient method is proposed for improving the uniformity of the RF field generated by a surface helical coil with nonlinearly distributed turns. An optimal law of the distribution of the turns of a helical coil is suggested. The results of a computer simulation of the field produced by this coil are presented and compared with the data for a conventionally used coil in the form of a linear spiral. The coils were tested during detection of nuclear quadrupole resonance signals on ¹⁴N nuclei in a (CH₂)₆N₄polycrystal and demonstrated the efficiency of the technique proposed for improving the field uniformity.     

利用热管技术提高土壤源热泵水平埋管换热效能

提出了把热管应用到土壤源热泵的水平埋管换热器中，用以提高换热器周围土壤的温度和稳定土壤的温度场，以减少埋管换热器的占地面积。     

线性测微电感的精化

为提高测微电感传感器的测量精度,提出了基于赫姆霍兹线圈理论设计螺线管线圈的方法,改善了螺线管线圈内轴向上磁场的分布均匀性。首先,分析了螺线管线圈模型,建立了螺线管线圈参数与轴向磁场强度分布相互关系的广义函数模型。然后,通过线圈与磁芯的尺寸确定了系统轴向磁场强度分布函数模型,结合磁芯移动区间范围设置磁场均匀度最小误差目标函数,通过对目标函数寻优得到各螺线管线圈的各项参数。最后,搭建了测微电感传感器的测试系统,测试了传感器性能。实验结果表明:与传统线圈相比,改进型螺线管线圈在100μm测量范围内的线性度由0.46%提高到0.30%。实验显示通过对不同规格的螺线管线圈进行组合,可使得螺线管内轴向上磁场强度分布均匀,从而提高了测量精度。     

Design and testing of a 1.5 Tesla double-tuned (H/P) RF surface coil with intrinsic geometric isolation

We analyse the isolation characteristics of axial and transverse field surface radio frequency coils, used to design a double-tuned surface coil composed by two coils, that combine proton (¹H) detection and localized spectra of phosphorous (³¹P). Several geometrical configurations were analysed, including circular loop and figure-of-eight coils, with the aim to optimize the isolation between the two channels. Our analysis shows that by using at least one transverse coil for the design of the double-tuned probe, it is possible to achieve a good intrinsic geometrical decoupling, without the need of additional decoupling circuits. On the basis of the experimental results, we have designed and built a 1.5 T double-tuned probe composed by a circular loop coil and a transverse field coil, with the external coil tuned at the ¹H frequency and the internal coil tuned at the ³¹P frequency, that shows a good intrinsic decoupling and signal-to-noise ratio.     

一种任意正交折线线圈阻抗的解析建模新方法

提出了一种位于导体上方正交折线线圈的阻抗解析建模方法。首先,在前人研究的基础上,定义了外形位置因子,得出了单矩形线圈的入射场感应电压及散射场电压简化计算方法;其次,将多个矩形线圈自感电压及两两之间的互感电压叠加,建立了串联等效电感模型;再次,根据任意正交折线线圈的几何原理,将该线圈拆解为有限个相同截面的矩形线圈并进行重构,得出入射场阻抗及散射场阻抗的广义二重积分表达式。最后,利用Mathematica对回折线圈实例进行了计算与实验比较,并根据影响阻抗的各个变量绘制阻抗平面图。拆解重构方法可用于不同形状、不同激励频率、不同提离高度的正交折线线圈平行置于任意电导率导体上方的阻抗解析计算。     

Switching frequency response characteristics of a low cost wireless power driving and controlling system for electrically tunable liquid crystal microlenses

The essential switching frequency response characteristics of a low cost wireless power driving and controlling system for electrically tunable liquid crystal microlenses (ETLCMs) are obtained. The wireless power system is mainly composed of two coils with different radius and winding as well as a power metal-oxide-semiconductor field effect transistor switch. The voltage response in the small coil, which is connected directly with ETLCMs, is measured and analyzed under the condition of changing some key parameters of the coil system, such as the width of switching frequency region and the duty-cycle of the switching signal ranging from 20% to 80% in intervals of 20%. Through extending the switching frequency range to a few hundreds of kilohertz, an attractive property of only modulating switching frequency to tune precisely the rms voltage in the small coil for ETLCMs is presented. Some interesting phenomena in high frequency regions, for instance, the rms voltage being stable or slightly changed as the frequency, the voltage response cutoff or disappearance after the frequency surpassing a threshold value, and then regeneration after lowering the frequency to lower frequency point than that of generating voltage response cutoff during increasing frequency, are also discovered.     

Characterization of a linear device developed for research on advanced plasma imaging and dynamics

Within the scope of long term research on imaging diagnostics for steady-state plasmas and understanding of edge plasma physics through diagnostics with conventional spectroscopic methods, we have constructed a linear electron cyclotron resonance (ECR) plasma device named Research on Advanced Plasma Imaging and Dynamics (RAPID). It has a variety of axial magnetic field profiles provided by eight water-cooled magnetic coils and two dc power supplies. The positions of the magnetic coils are freely adjustable along the axial direction and the power supplies can be operated with many combinations of electrical wiring to the coils. Here, a 6 kW 2.45 GHz magnetron is used to produce steady-state hydrogen, helium, and argon plasmas with central magnetic fields of 875 and/or 437.5 G (second harmonic). In order to achieve the highest possible plasma performance within the limited input parameters, wall conditioning experiments were carried out. Chamber bake-out was achieved with heating coils that were wound covering the vessel, and long-pulse electron cyclotron heating discharge cleaning was also followed after 4 days of bake-out. A uniform bake-out temperature (150?°C) was achieved by wrapping the vessel in high temperature thermal insulation textile and by controlling the heating coil current using a digital control system. The partial pressure changes were observed using a residual gas analyzer, and a total system pressure of 5×10(-8)?Torr was finally reached. Diagnostic systems including a millimeter-wave interferometer, a high resolution survey spectrometer, a Langmuir probe, and an ultrasoft x-ray detector were used to provide the evidence that the plasma performance was improved as we desired. In this work, we present characterization of the RAPID device for various system conditions and configurations.     

用于磁电阻率探测的矢量线圈传感器设计与优化

磁电阻率(MMR)探测方法作为一种新型的堤坝渗漏探测方法,采集数据时主要依靠线圈传感器,针对MMR信号对要求灵敏度高,需要精准矢量采集的特点,本文设计了一款三分量MMR空心线圈传感器。通过对传感器灵敏度与线圈结构参数的分析,对线圈的结构、匝数进行了设计;通过对传感器噪声源分析,选定了适宜的放大器,进一步降低了系统的本底噪声;通过对三分量不正交角度的分析,对线圈的不正交角度进行了参数校正。最终研制了一款三分量MMR线圈传感器。其体积控制在0.027m3,X、Y、Z三分量本底噪声为5.030 435nV/(Hz)^1/2@380Hz,三通道的磁场探测灵敏度为0.189 95pT/(Hz)^1/2@380Hz,三通道一致性良好,三分量校正误差控制在0.2%以内。     

New printed circuit boards magnetic coils in the vacuum vessel of J-TEXT tokamak for position measurement

Four sets of magnetic diagnostic coils, which are printed on machinable ceramic printed circuit boards (PCB), are designed, fabricated, installed, and tested in the Joint Texas Experimental Tokamak (J-TEXT) vacuum vessel for detecting the plasma radial and vertical displacements relative to the geometric center of the vacuum vessel in Ohmic discharges. Each coordinate is determined by a pair of variable cross-section Rogowski and saddle coils, which measure the tangential and normal magnetic fields (relative to the coil surface). These coils are suitable for mass production and offer advantages in vacuum compatibility and temperature tolerance that are important for J-TEXT. Position measurements using PCB coils are compared with those from soft x-ray image system and match the position well.