Calculation Of Field Distribution Research Articles

Design, fabrication and test of high temperature superconducting magnet for heat flux and radio blackout mitigation experiments in plasma wind tunnels

High heat flux and radio blackout are well-known challenges space vehicles have been facing during re-entry into a planet’s atmosphere since the early days of space-flight. Thermal protection systems have been developed to protect spacecraft and astronauts, however, they are often heavy and some have to be replaced after each mission. High temperatures in the compressed gas in the shock wave lead to partial ionization. The dense plasma can cause radio blackout, i.e. attenuation or reflection of radio waves thus blocking data-telemetry and communication with ground stations or satellites. One approach to solve both problems is to influence the plasma with magnetohydrodynamic effects using a strong magnet. In the framework of the European project MEESST (Magnetohydrodynamic Enhanced Entry System for Space Transportation) heat flux mitigation and radio blackout mitigation is investigated by means of modelling and ground experiments in plasma wind tunnels at the Institute of Space Systems (Stuttgart, Germany) and at the Von Karman Institute for Fluid Dynamics (Brussels, Belgium) using an HTS magnet. After a short introduction to the scientific background of the MEESST project, the boundary conditions for the design of the magnet and calculations of field distributions are presented. The pancake coils of the magnet were wound with a robotic winding system. Results from a preliminary test of the conduction-cooled magnet are presented.

Numerical simulation of magnetization induction coupled discharge plasma discharge process

Abstract First, this paper analyzes the plasma discharge and fluid model, and constructs the plasma discharge model by drift-diffusion approximation control equation, heavy particle component control equation, electric field distribution and volume force calculation, and plasma chemical kinetic model. Next, the coupling mechanism of inductively coupled RF plasma and its discharge characteristics are analyzed. Finally, the magnetized inductively coupled plasma discharge is simulated numerically. The results demonstrate that the current flowing on an inductor coil develops quicker at 0.045T and then calms down with an increase in the supplied constant dynamic magnetic field power, but the coil voltage exhibits the reverse effect.

Магнитное поле многовитковой цилиндрической катушки с ферромагнитным сердечником в непосредственной близости от металлических конструкций в задаче поиска людей под завалами в шахтах

Some aspects of the low-frequency magnetic field propagation in heterogeneous medium in mines are discussed in the paper. The theoretical model for calculation of magnetic field distribution in case of the parallel axis of transmitting antenna and bulk metal is developed. Metal structures are rail tracks, magnetic antenna is multiturn cylindrical coil with ferromagnetic core. Magnetic field according to proposed models principle in several stages using the method of integral equations was numerical calculated. This method of calculation of magnetic field in considered inhomogeneous space is based. The calculations of magnetic field strength of the multiturn cylindrical coil with ferromagnetic core in nearby proximity and at various distances from bulk metal were carried out. The possibility of use of low-frequency magnetic field attenuation for people search under avalanches was proved.

Polarization-selective narrow band dual-toroidal-dipole resonances in a symmetry-broken dielectric tetramer metamaterial.

Here we propose a metasurface consisting of symmetry-broken dielectric tetramer arrays, which can generate polarization-selective dual-band toroidal dipole resonances (TDR) with ultra-narrow linewidth in the near-infrared region. We found, by breaking the C4v symmetry of the tetramer arrays, two narrow-band TDRs can be created with the linewidth reaching ∼ 1.5 nm. Multipolar decomposition of scattering power and electromagnetic field distribution calculations confirm the nature of TDRs. A 100% modulation depth in light absorption and selective field confinement has been demonstrated theoretically by simply changing the polarization orientation of the exciting light. Intriguingly, it is also found that absorption responses of TDRs on polarization angle follow the equation of Malus' law in this metasurface. Furthermore, the dual-band toroidal resonances are proposed to sense the birefringence of an anisotropic medium. Such polarization-tunable dual toroidal dipole resonances with ultra-narrow bandwidth offered by this structure may find potential applications in optical switching, storage, polarization detection, and light emitting devices.

Analytical Calculation of Air-Gap Magnetic Field Distribution in IPMSMs with Mixed Eccentricity Accounting for Bridge Saturation

This paper presents an analytical model for calculating the detailed air-gap magnetic field distribution in interior permanent magnet synchronous motors (IPMSMs) with mixed eccentricity. In order to improve the efficiency of model solving, a modeling strategy combining the equivalent magnetic circuit network method and the subdomain method was adopted. Specifically, the magnetic field distribution of the rotor was modeled by using the magnetic circuit analysis method, and the magnetic field distributions of the air-gap, slot opening and stator slot along the radial direction were modeled in different regions according to their structure ruler. Then, the influence of bridge saturation was considered. Moreover, based on the analysis of the air-gap geometric structure with mixed eccentricity, a detailed spatiotemporal analytical model of the air-gap magnetic field was established, which provides a more accurate description of the mixed eccentricity composed of static and dynamic rotor eccentricities of different severity. The analytical models were compared with the corresponding models established by the finite element method, which proved the accuracy and validity of the models established in this paper. Finally, some key features related to radial and tangential air-gap flux density were extracted, which can significantly reflect the characteristics of eccentricities. The main findings reported in this paper will be of benefit for developing methods for early identification and diagnosis of eccentricity faults in IPMSMs.

Particle orbit optimization in the beam extraction region of a cold cathode PIG negative ion source for electrostatic tandem accelerators

When using a PIG (Penning Ion Gauge) type ion source for production of negative ions, these ions must be extracted from a hole on the side of the anode cylinder, perpendicularly to the magnetic field for plasma confinement. As a result, unnecessary deflection force works on the extracted beam. This study aims to improve the ion extraction efficiency of a cold-cathode PIG negative-ion source. The idea is to reduce the beam loss by cancelling the stray magnetic field from the source by placing small dipole magnets in the extraction electrode. Through the measurement of the magnetic field distribution and beam trajectory calculation, it was numerically confirmed that the beam trajectory can be corrected by this small dipole magnet with a peak magnetic field of about 50 mT under the present experimental condition.

Achieving Low Threshold and High Optical Gain Amplified Spontaneous Emission in MAPbI3 Perovskite Films via Symmetric Waveguide Effect

AbstractLead halide perovskites are attractive light source candidates for new amplifiers and lasers in the growing field of short‐distance data communication. However, the presence of plenty of defects and poor stability are the major obstacle to the production and application of perovskite optoelectronic devices. Three strategies are proposed to prepare MAPbI3 perovskite films with high stability and enhanced light amplification in this study: 1) MAPbI3 films are prepared with ionic liquid methylammonium acetate (MAAc) to improve the quality of the films; 2) a poly(methyl methacrylate) (PMMA) passivation layer is used to improve the optical and thermal stability of the MAPbI3 film; 3) a symmetric waveguide (SWG) structure is designed to enhance the amplified spontaneous emission (ASE) properties of the MAPbI3 film. The formed SWG exhibits increased mode confinement and reduced propagation loss, thus enabling a lower ASE threshold, a higher optical gain and improved photostability, thermal and humidity stability compared with the pristine MAPbI3 film. Femtosecond transient absorption spectroscopy and electric field distribution calculation are utilized to elucidate the carrier dynamics and carrier‐phonon effect and the microscopic origin of the observed effects of functionalization. This study indicates the possibility of simple and effective approaches for realizing efficient ASE and lasing.

A Feasibility Study of an Optimization-Based Active Field Uniformity Compensation Method for Superconducting Magnets

In order to enhance the quality of measurement results of various scientific instruments, such as magnetic property measurement systems, magnetic resonance imaging (MRI), nuclear magnetic resonance (NMR) and others, a spatially uniform magnetic field is required at the magnetic center. However, the measured field uniformity is usually worse than that in the design result due to the manufacturing errors of a superconducting magnet system. Therefore, spatial field uniformity compensation is needed to reduce the effects of manufacturing errors on field uniformity. Conventional field compensation methods require recursive routines of field mapping and compensation coil current adjustments, which lead to a less effective time-consuming process. In this study, a recently developed active field compensation algorithm employing pattern search, an optimization theory, will be introduced. A MATLAB code for active compensation coil current calculations with pattern search was developed, and six compensation coil designs and field distribution calculations with and without the proposed method were also carried out to compare the results. The test results demonstrate the feasibility of the proposed field compensation method for superconducting magnets.

Fast Calculation of Acoustic Field Distribution for Ultrasonic Transducers Using Look-Up Table Method

The point source superposition method based on the Rayleigh integral model is time-consuming for calculating the three-dimensional spatial sound field. In this paper, the look-up table method is introduced into the calculation of the acoustic field to reduce the computational effort. Based on the region of synchronous vibration on the transducer, a sub-regional look-up table method is proposed. Simulations demonstrate that both the acoustic field look-up table (ALUT) method and the acoustic field sub-regional look-up table (ASLUT) method have the same acoustic field calculation results as the point source method. Regarding the cost of time, the acoustic field look-up table method takes only one third of the time of the point source method, and the acoustic field sub-region look-up table method takes only one eighteenth of the time of the point source method, with the possibility of further reduction. Both the ALUT and ASLUT methods significantly reduce the calculation time for different types of transducers, which is beneficial for the study of planar sound source devices.

Coupled Electromagnetic-Thermal Model Applicable for Distribution Transformers

Distribution transformers, with their specific passive cooling mechanism, are investigated in this research. FEM based approach was used for electromagnetic field distribution and losses calculation, following with the methodology for thermal modelling. Detailed temperature measurements using thermocouples and thermal camera were done on 1600 kVA unit, the results of which are compared against calculated values. The aim of this research is to present a viable approach for adequate thermal modelling of distribution transformers applicable for research and design purposes.

Highly sensitive biosensor based on an all-dielectric asymmetric ring metasurface.

We propose an all-dielectric asymmetric ring-cylindrical metasurface. Based on the analysis of transmission characteristics and the calculation of electromagnetic field distribution of the metasurface with this element structure, it is found that the high Q resonance of the ultra-narrowband can be realized when the symmetry of the ring-cylindrical structure is broken. Meanwhile, it is found that the degree of asymmetry of the ring, the refractive index of the material, the radius of the ring, and the substrate have great influence on the Q value and resonant frequency of the metasurface. Our proposed metasurface structure is applied to the detection of biological molecules based on the change in refractive index of biomolecular solutions. The designed metasurface with high sensitivity to detect biomolecules with different refractive indices, the Q value can reach 365.03, and the sensitivity is increased by 90.36 GHz/RIU compared to that without substrate, while the figure of merit value is as high as 100.56, providing label-free detection of biomolecules.

Transmission efficiency and beam reception of the SESRI 300 MeV synchrotron injection line

SESRI 300 MeV synchrotron in Harbin Institute of Technology is now under construction and the whole equipment has been installed and tested. Before commissioning beam, the beam transport through the injection line is simulated by using a full-scall model through the Tracewin code. The field distribution of RFQ cavity is calculated with CST, and the results are substituted into the Tracewin code to generate the accurate results. The envelop mode and multi-particles mode are used in the beam simulation with two typical beams (H<inline-formula><tex-math id="Z-20220529151953">\begin{document}${}_2^+ $\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="11-20212112_Z-20220529151953.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="11-20212112_Z-20220529151953.png"/></alternatives></inline-formula> and <sup>209</sup>Bi<sup>32+</sup>, the lightest beam and the heaviest beam). Both beams are accelerated from 4 keV/u to 2 MeV/u by an RFQ cavity and two IH-DTL cavities. Then the H<inline-formula><tex-math id="Z-20220529152018">\begin{document}${}_2^+ $\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="11-20212112_Z-20220529152018.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="11-20212112_Z-20220529152018.png"/></alternatives></inline-formula> beam is stripped into a proton beam by a carbon foil and accelerated to 5.6 MeV with the third IH-DTL cavity. Simulation results show that the strength of the magnetic field and the acceleration field are proportional to the mass charge ratio. The beam transmission efficiency and the injection line reception are inversely proportional to the beam transverse emittance. The <sup>209</sup>Bi<sup>32+</sup> beam transmission efficiency and beam reception (momentum spread less than ±0.2%) are 72.16% and 46.72% with transverse emittance <i>ε</i> = 0.12π mm·mrad (ECR source output) and <i>ε</i> = 0.4π mm·mrad (RFQ output). H<inline-formula><tex-math id="Z-20220529152204">\begin{document}${}_2^+ $\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="11-20212112_Z-20220529152204.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="11-20212112_Z-20220529152204.png"/></alternatives></inline-formula> beam transmission ratio and beam reception are 24.19% and 17.89% with <i>ε</i> = 0.2π mm·mrad (ECR source output) and <i>ε</i> = 0.5π mm·mrad (RFQ output). In order to obtain high transmission efficiency and beam reception, the transverse emittance should be limited to 0.1π mm·mrad after the RFQ. With this limitation, the <sup>209</sup>Bi<sup>32+</sup> beam transmission efficiency and the reception are increased to 96.68% and 92.63%, respectively, and the H<inline-formula><tex-math id="Z-20220529152129">\begin{document}${}_2^+ $\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="11-20212112_Z-20220529152129.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="11-20212112_Z-20220529152129.png"/></alternatives></inline-formula> beam transmission efficiency and the rception rise to 74.40% and 68.18%, respectively. If two additional quadrupole magnets are added, the H<inline-formula><tex-math id="Z-20220529152030">\begin{document}${}_2^+ $\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="11-20212112_Z-20220529152030.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="11-20212112_Z-20220529152030.png"/></alternatives></inline-formula> beam transmission efficiency and beam reception can be increased to 90.73% and 83.61%, respectively, which will fulfill the requirement for long-time operation. The phase space change process shows that loss of <sup>209</sup>Bi<sup>32+</sup> beam is caused mainly by longitudinal defocusing (energy spread and phase width spread), the loss of proton beam is caused both by the longitudinal defocusing and by the transverse defocusing (beam envelop spreading), that is why two additional focusing magnets should be added in proton beam acceleration. Results also show that by using field distribution calculation in the simulation process the greater influence of the cavity design details can be confirmed such as beam off-axis caused by dipole field in the IH-DTL cavity and beam loss caused by unperfect field in the RFQ. Tracking with field distribution is shown to be a useful method to link the cavity design process, beam line design process, and beam commission process.

Magnetic field and electromagnetic performance analysis of permanent magnet machines with segmented Halbach array

PurposeThis study aims to accurately calculate the magnetic field distribution, which is a prerequisite for pre-design and optimization of electromagnetic performance. Accurate calculation of magnetic field distribution is a prerequisite for pre-design and optimization.Design/methodology/approachThis paper proposes an analytical model of permanent magnet machines with segmented Halbach array (SHA-PMMs) to predict the magnetic field distribution and electromagnetic performance. The field problem is divided into four subdomains, i.e. permanent magnet, air-gap, stator slot and slot opening. The Poisson’s equation or Laplace’s equation of magnetic vector potential for each subdomain is solved. The field’s solution is obtained by applying the boundary conditions. The electromagnetic performances, such as magnetic flux density, unbalanced magnetic force, cogging torque and electromagnetic torque, are analytically predicted. Then, the influence of design parameters on the torque is explored by using the analytical model.FindingsThe finite element analysis and prototype experiments verify the analytical model’s accuracy. Adjusting the design parameters, e.g. segments per pole and air-gap length, can effectively increase the electromagnetic torque and simultaneously reduce the torque ripple.Originality/valueThe main contribution of this paper is to develop an accurate magnetic field analytical model of the SHA-PMMs. It can precisely describe complex topology, e.g. arbitrary segmented Halbach array and semi-closed slots, etc., and can quickly predict the magnetic field distribution and electromagnetic performance simultaneously.

Analytical calculation and finite element evaluation of electromagnetic leakage field distribution in surface-mounted permanent magnet synchronous motors taking the rotor eccentricity effect into account

PurposeThe purpose of this paper is to present an analytical calculation for estimating the leakages field distribution in surface-mounted permanent magnet synchronous motors (SMPMSMs) according to a sub-domain field model for eccentricity fault detection.Design/methodology/approachThe magnetic field domain is classified into four sub-domains of PMs, air gap, stator core and outer region. In the proposed method, the governing equations taking the rotor eccentricity effect into account per region and the interface boundary conditions between sub-domains are formulated using the regular perturbation technique, Taylor series and Fourier series expansion. Maxwell's equations are solved in different regions in the polar coordinate system regarding the boundary conditions.FindingsThe radial and tangential components of electromagnetic field distribution in all sub-domains of one SMPMSM are obtained using the proposed method analytically. Finite element analysis is used to validate the results of the proposed method; the results indicated that the analytical model matches the finite-element prediction up to 30% eccentricity, except for some peak values that depend on the harmonic order value. The results of this paper demonstrated that in the event of eccentricity, an asymmetric magnetic field is generated in the outer region of the machine. Although its amplitude is small, it can be an indicator for detecting eccentricity faults from the outside environment of the machine.Originality/valueThe formulas presented in this paper can be applied as a new technique for detecting eccentricity faults in these motors from the outside environment.

Rapid Analytical Calculation of Magnetic Field and Critical Current Distributions in HTS Magnets

For the design of superconducting magnets, the magnetic field and critical current distributions are usually calculated based on finite element software such as COMSOL, ANSYS, etc. These software are necessary for accurate structure modeling and field calculation, but they occupy large memory space and comsume long simulation time. Furthermore, they are not easy to use. To achieve an easy-to-implement solution for rapid magnet field and critical current calculations, this paper investigates three types of analytical calculating methods, and builds an autonomously-operated calculating application program (APP) for the uses in various superconducting magnets.

Refined modeling calculation of electromagnetic fields when lightning strikes thermal power plant and optimized layouts of sensitive devices

Lightning strikes thermal power plant will affect the normal operation of sensitive devices. However, due to the complex structure of thermal power plant, the calculation of electromagnetic field distribution is not accurate, and there is a lack of lightning protection specifications for low-voltage systems. Firstly, taking a thermal power plant in China as the object, an electromagnetic model of the low-voltage system including large irregular grounding grids, transformers, distribution lines, overhead cable trays, and external lightning protection systems is established, and a calculation method suitable for spatial electromagnetic fields of the complex model of thermal power plant is proposed. Secondly, the method is applied to the calculation of the maximum value of the magnetic fields at different layers, and the results show that the calculation accuracy is greatly improved. Finally, a method for optimizing the spatial layouts of sensitive devices in thermal power plant is proposed. This article provides data support for the design specifications and standards for lightning protection of low-voltage systems in thermal power plant. The spatial layouts of sensitive devices are optimized to achieve the purpose of rational use of building spatial and saving engineering costs.

Increasing the efficiency of multy-variant calculations of electromagnetic field distribution in matrix of a polygradient separator

An approach is proposed to carry out multivariate calculations of the magnetic field distribution in the working gaps of a plate polygradient matrix of an electromagnetic separator, based on a combination of the advantages of two- and three-dimensional computer modeling. Two-dimensional geometric models of computational domains are developed, which differ in the geometric dimensions of the plate matrix elements and working air gaps. To determine the vector magnetic potential at the boundaries of two-dimensional computational domains, a computational 3D experiment is carried out. For this, three variants of the electromagnetic separator are selected, which differ in the size of the working air gaps of the polygradient matrices. For them, three-dimensional computer models are built, the spatial distribution of the magnetic field in the working intervals of the electromagnetic separator matrix and the obtained numerical values of the vector magnetic potential at the boundaries of the computational domains are investigated. The determination of the values of the vector magnetic potential for all other models is carried out by interpolation. The obtained values of the vector magnetic potential are used to set the boundary conditions in a computational 2D experiment. An approach to the choice of a rational version of a lamellar matrix is substantiated, which provides a solution to the problem according to the criterion of the effective area of the working area. Using the method of simple enumeration, a variant of the structure of a polygradient matrix with rational geometric parameters is selected. The productivity of the electromagnetic separator with rational geometric parameters of the matrix increased by 3–5 % with the same efficiency of extraction of ferromagnetic inclusions in comparison with the basic version of the device

Calculation of Electric Fields in HVDC Cables: Comparison of Different Models

This paper presents a comparison of different models used for calculations of electric field distributions in HVDC cable insulation. Calculated electric field and space charge distributions for a loaded 320 kV HVDC cable are compared with the experimental characteristics reported in the literature. Additionally, for selected models, a sensitivity of the results to variations of the model parameters is analyzed. It is noticed that the calculations utilizing the empirical expressions for the field and temperature dependent electric conductivities (Le., macroscopic approach) allowed for predicting so-called field inversion phenomena under DC stresses. It is found, however, that such models are not capable of predicting the magnitudes of the maximum field stress and polarity of the accumulated space charges accurately. Models based on bipolar charge transport (i.e., microscopic approach) in addition to the effects described by the macroscopic models, predict the experimentally observed accumulation of homo- and hetero-charge in the insulation reasonably well. It is concluded that the microscopic approach has been used with proper descriptions of the rates and parameters of physical processes of the transport, generation and losses of charged species in the bulk of the insulation, as well as of its interfaces, provides convincing electric field estimations for HVDC cables. Because of the uncertainty in model parameters, the accuracy of DC field calculations is less than the high accuracy of AC calculations for HVAC cables that we are used to.

Double Narrow Notch Spectral Filter Design Using Waveguide Grating on Metal Substrate

A double narrow notch spectral filter design using planar dielectric grating diffraction coupled resonant thin dielectric waveguide on metal substrate is numerically studied in this article. Due to excitation and coupling of guided resonance mode in thin dielectric waveguide layer and surface plasmon mode on the interface between the waveguide and the metal substrate, double deep and narrow reflection spectrum dip can be obtained. This physical explanation is confirmed by the momentum matching conditions of resonance and the field distribution calculation. As an example, double notch filter design with full width half maximum less than 2 nm centered at 549 nm and 651 nm is presented.

Analytical Calculation of Magnetic Field in Fractional-Slot Windings Linear Phase-Shifting Transformer Based on Exact Subdomain Model

Fractional-slot windings linear phase-shifting transformers (FW-LPSTs) are a new type of transformer that can be used as an important component of multi-rectifier and multi-inverter systems. The FW-LPSTs are proposed for the first time, and few scholars have studied their magnetic field. However, accurate calculation of magnetic field distribution of the FW-LPSTs is the premise of the optimal design of the ontology, and the establishment of an accurate analytical model which remains a challenging task is the key to solving the magnetic field distribution. In view of the limitation of traditional analytical theory in solving the magnetic field, the FW-LPST model based on the exact subdomain method is proposed to obtain the exact magnetic field distribution. Considering the influences of the permeability and the structural parameters of the slot subdomain and the interaction of all slots on the distribution of the magnetic field, the governing equations of the air gap and slot subdomains are established using magnetic vector potential as the variable. According to the boundary conditions of each subdomain, all equations of the boundary condition are listed based on the Fourier series method. Finally, the vector magnetic potential and open-circuit magnetic flux density distribution of each subdomain are solved. The model accurately analyzes the influence of the cogging effect on the magnetic field distribution. The inductances of the primary side and the induced potentials of the secondary side are solved using the magnetic flux linkage method. The accuracy of the proposed analytical model is verified by comparison of the results obtained with those obtained by the finite element method.