Toroidal Magnet Research Articles

Single-Molecule Toroic Design through Magnetic Exchange Coupling

Summary Toroidal molecular magnets represent promising candidates for next-generation ultra-dense information storage. These wheel-like molecules are able to store one bit per molecule because of their insensitivity to homogeneous magnetic fields—one of the main sources of magnetic perturbations. However, synthesis of molecules possessing a well-defined and stable vortex arrangement of the on-site magnetic moments in the ground state represents a challenge. Here, we show that 16 magnetic metal ions can be alternately arranged into a macrocycle named {Fe8Dy8}. The net toroidal moment can be experimentally determined at 0.23 Tesla. Moreover, ab initio calculations were performed to reveal that ferromagnetic exchange interactions between the FeIII and DyIII metal centers are the key to generate this toroidal moment. This feature is significantly distinguished from the previously described dipole-dipole interaction-based single-molecule toroics (SMTs), showing the importance of exchange-coupling interactions in the design of next-generation SMTs.

Electro-Magnetic Design of a 3MJ YBCO Magnet

The electro-magnetic design of two 3 MJ superconducting magnetic energy storage (SMES) magnets with YBCO conductor are presented. One magnet is with solenoidal geometry composed of double pancake coils, and the other one is with toroidal geometry. According to the magnetic field simulation results, the perpendicular componet of the magnetic field of the toroidal magnet could be extremely reduced compared with the solenoidal geometry. Therefore, a lower YBCO conductor requirement could be expected due to the dependence of Jc vs B performance of the YBCO conductor. Besides, the lower leakage magnetic field is important for application. A SMES system of 3 MJ is considered, and the coil is made of multiple identical D-type pancake coils. The critical current of the used YBCO conductor at 30K is 270A under 1 T perpendicular magnetic field. The inner radius of the D-type curve is 500 mm, and the outer radius is 1000 mm. The SMES magnet is made of 96 pancake coils, where the rated operating current is 975 A and the maximum perpendicular and parallel magnetic flux density are 0.5 T and 4.0 T, respectively. Further more, the maximum hoop stress and radial stress are 283 MPa and 78 MPa.

Design updates and analysis of the Korean fusion demonstration reactor superconducting toroidal field magnet system

Abstract After a conceptual design study for a steady-state Korean fusion demonstration reactor (K-DEMO) was initiated in 2012, the preliminary design of superconducting magnet system which is one of the key components of the K-DEMO has been done in 2015. The superconducting magnet system of K-DEMO has 16 Toroidal Field (TF) coils, 8 Central Solenoids (CS) modules and 12 Poloidal Field (PF) coils which use Cable-In-Conduit Conductors (CICC). For a high 7.4 T magnetic field generation at plasma center, high performance Nb3Sn based superconductor will be developed and used for TF magnet. Starting from the preliminary conceptual design, design updates of K-DEMO TF magnet is being conducted for checking engineering issues. For a validation of the magnet design, thermo-hydraulic stability and mechanical stability are being considered. In this work, the conceptual design studies for updates of K-DEMO TF magnet system is described.

Conceptual design of a high temperature superconducting magnet for a particle physics experiment in space

In the frame of a collaboration between CERN, ASI, University of Trento, and TIFPA, the HTS demonstrator magnet for space project has started to define methods and procedures for manufacturing high temperature superconducting magnets for space applications. To this purpose, we developed a conceptual design of a superconducting magnetic spectrometer for a physics experiment in space. The configuration is a toroid with twelve superconducting coils based on ReBCO tape. By using ReBCO tape with an engineering critical current density, Je, exceeding 1000 A mm−2 at and , as reached in the H2020-ARIES program, the magnet system provides an average bending strength of . This is sufficient to measure charged particles with rigidities up to , more than two orders of magnitude higher than the present state-of-the-art space spectrometer. The magnet system requires about of ReBCO tape and produces a peak magnetic field of at an operating temperature of . A small scale single coil, which is about one third in size of a coil from the toroidal magnet system, will be manufactured and tested as demonstrator of the magnet technology. The mechanical structure and performance of the toroidal magnet system and demonstrator coil are described.

The CLAS12 drift chamber system

The CEBAF Large Acceptance Spectrometer at 12 GeV (CLAS12) is located in Hall B, one of the experimental halls at Jefferson Lab. The forward part of CLAS12 is built around a superconducting toroidal magnet. The six coils of the toroid divide the detector azimuthally into six sectors. Each sector contains three multi-layer drift chambers for reconstructing the trajectories of charged particles originating from a fixed target.Each of the 18 planar chambers has two “superlayers” of six layers each, with the wires in the two adjacent superlayers oriented at ±6° stereo angles. Each layer has 112 hexagonal cells spanning a range from about 5° to 40° in polar angle. The six-layer structure provides redundancy in track segment finding and good tracking efficiency even in the presence of some individual wire inefficiency. The design, construction, operation, and calibration methods are described, and estimates of the efficiency and resolution are presented from in-beam measurements.

Safety analysis of the 100 kA HTS current lead for CFETR

Based on the Agreement of Institute of Plasma Physics Chinese Academy of Sciences (ASIPP) and Ministry of Science and Technology of China during the Thirteen Five-Years Plan (so called 13∙5 plan), a dedicated test facility of superconducting magnet for China Fusion Engineering Test Reactor (CFETR) will be constructed in Hefei, China. A pair of high temperature superconducting (HTS) current leads rated at 100 kA for the CFETR magnet test facility is being designed at ASIPP. Because magnetic energy stored in the toroidal field magnet is 134 Giga Joules which are 3 times higher than the ITER case, HTS current leads must work at nominal current without performance degradation during the HTS current lead quench. In order to verify the safety and reliability of HTS current lead, the analysis of static magnetic field is done by ANSYS iteration to predict the maximum current carrying capacity of HTS module. This paper also give the numerical calculation of loss of flow accident(LOFA) of HTS current lead and temperature margin analysis of HTS module. The analysis results indicate that the HTS module has a current carrying capacity of 165 kA without external field at 65 K and a current carrying capacity of 149 kA with external 30 mT vertical field at 65 K. The LOFA time is about 580 s and the burnout time is about 30 s, which is better than the requirement of the toroidal field coil fast discharge time of 24 s.

The CLAS12 Spectrometer at Jefferson Laboratory

The CEBAF Large Acceptance Spectrometer for operation at 12 GeV beam energy (CLAS12) in Hall B at Jefferson Laboratory is used to study electro-induced nuclear and hadronic reactions. This spectrometer provides efficient detection of charged and neutral particles over a large fraction of the full solid angle. CLAS12 has been part of the energy-doubling project of Jefferson Lab’s Continuous Electron Beam Accelerator Facility, funded by the United States Department of Energy. An international collaboration of 48 institutions contributed to the design and construction of detector hardware, developed the software packages for the simulation of complex event patterns, and commissioned the detector systems. CLAS12 is based on a dual-magnet system with a superconducting torus magnet that provides a largely azimuthal field distribution that covers the forward polar angle range up to 35∘, and a solenoid magnet and detector covering the polar angles from 35° to 125° with full azimuthal coverage. Trajectory reconstruction in the forward direction using drift chambers and in the central direction using a vertex tracker results in momentum resolutions of <1% and <3%, respectively. Cherenkov counters, time-of-flight scintillators, and electromagnetic calorimeters provide good particle identification. Fast triggering and high data-acquisition rates allow operation at a luminosity of 1035 cm−2s−1. These capabilities are being used in a broad program to study the structure and interactions of nucleons, nuclei, and mesons, using polarized and unpolarized electron beams and targets for beam energies up to 11 GeV. This paper gives a general description of the design, construction, and performance of CLAS12.

AC Loss Measurement of the DEMO TF React&amp;Wind Conductor Prototype No. 2

The EUROfusion DEMO is being designed as the fusion machine to be built after ITER. During the preconceptual phase, several design options are investigated by theoretical analyses as well as tests on newly developed conductor prototypes. One design option for the toroidal field magnet (TF) and central solenoid (CS) is based on flat Nb 3 Sn forced-flow conductors made with react&wind technique. The usage of these conductors simplifies some steps in the conductor and coil manufacturing, and together with graded layer-winding allows approx. 50% reduction of the required amount of Nb 3 Sn compared to ITER-like design based on wind-react-insulate pancake-winding. Two full-size prototype cables for DEMO TF coil were manufactured, jacketed and tested in several test campaigns in SULTAN test facility. The DC results for the second prototype, RW2, rated for 63 kA at 12.3 T, were presented and published in 2018. The AC loss data were collected over several test campaigns performed on various assemblies of RW2 at AC field parallel and perpendicular to the broad cable side. The measurements done at 4.5 K and 20 K allow us to decompose the AC loss contributions originating from the bundle of superconducting strands (hysteresis and coupling loss) and copper-matrix stabilizer located around the cable. The AC loss for sinusoidal and trapezoidal field variations are presented and discussed. The low AC loss of the flat cable makes the cable an attractive choice for the central solenoid operating in a pulse mode.

Magnetic toroidal dipole response in individual all-dielectric nanodisk clusters.

Multipole electromagnetic resonances and their couplings are of crucial importance for both the fundamental understanding of light scattering by high-index all-dielectric nanostructures and lots of nanophotonic applications based on those nanostructures. Here, we show that magnetic dipole modes in a dielectric nanodisk cluster can easily form a magnetic toroidal dipole (MTD) mode. The cluster consists of five silicon nanodisks, where each nanodisk holds a magnetic dipole mode. These magnetic dipole modes can collectively couple with each other and form a MTD mode under suitable excitation. The MTD mode is confirmed by multipole expansion calculations and near field distributions, where two closed loops of magnetic field with opposite directions are seen. The response of the MTD is strong and comparable to that of a common electric dipole or magnetic dipole mode. It is also found that the MTD resonance is accompanied by an electric toroidal quadrupole mode in the cluster. The MTD mode is tunable by varying the geometries. We also fabricated silicon nanoparticle clusters and verified the MTD mode in the experiment. Our results illustrate the controllable excitation of strong high-order electromagnetic modes and these modes may open new opportunities for light manipulation at the nanoscale.

A Pseudodisk Threaded with a Toroidal and Pinched Poloidal Magnetic Field Morphology in the HH 211 Protostellar System

Abstract The HH 211 protostellar system is currently the youngest Class 0 system found with a rotating disk. We have mapped it at ∼50 au (0.″16) resolution, studying its magnetic field morphology with dust polarization in continuum at 232 and 358 GHz and its kinematics in C18O J = 2–1 line. A flattened envelope extending out to ∼400 au from the disk is detected in the continuum and C18O, slightly misaligned with the disk by ∼8°. It is spiraling inwards and expected to transform into a rotating disk at ∼20 au, consistent with the disk radius estimated before. It appears to have a constant specific angular momentum and it can result from an inside–out collapse of an extended envelope detected before in NH3. In the flattened envelope, the polarization is mainly due to the magnetically aligned dust grains, inferring a highly pinched poloidal field morphology there. Thus, both the kinematics and field morphology support that the flattened envelope is a pseudodisk formed as the infalling gas is guided by the field lines to the equatorial plane. Interestingly, a point-symmetric polarization distribution is also seen in the flattened envelope, implying that the pinched field lines also have a significant toroidal component generated by the rotation. No significant loss of angular momentum and thus no clear magnetic braking are detected in the flattened envelope around the disk probably because of the large misalignment between the axis of the rotation and the axis of the magnetic field in the cloud core.

Magnetic Vortex Induced by Nonmagnetic Impurity in Ferromagnets: Magnetic Multipole and Toroidal around the Vacancy

We report our theoretical study on nucleation of a magnetic vortex around a nonmagnetic impurity doped into ferromagnets. The mechanism lies in the asymmetric Dzyaloshinskii-Moriya interaction arising from the breaking of spatial inversion symmetry by the impurity. By using the spin-wave analysis and Monte Carlo simulations, we show that the asymmetric interaction induces a magnetic vortex with nonzero vorticity $l=+1$. The vortex is stabilized even for less frustration in exchange interactions and in the absence of an external magnetic field. We also find that the magnetic vortex is characterized by magnetic multipoles according to its vorticity and helicity. We demonstrate a potential realization of such a magnetic vortex by considering a monolayer ferromagnet on a nonmagnetic substrate, which results in the magnetic monopole and toroidal dipole.

Progress toward ITER’s First Plasma

ITER reached 50% completion of the work required to achieve First Plasma in November 2017. Progress has been made on ITER infrastructure since the 2016 Fusion Energy Conference, most visibly the construction of many key buildings. The key parts of the tokamak assembly building and the tokamak bioshield have been completed. The tokamak building itself will be ready for equipment in 2020. The cryogenic plant and the magnet power supply buildings are complete, and these systems begin commissioning in 2020. The power conversion and distribution area is complete and in operation, and construction has started on the component cooling water system building. Manufacturing of the basic components of the ITER tokamak is also proceeding well. The base and lower cylinder of the cryostat have been assembled on the ITER site. The first modules of the central solenoid and of the six poloidal field coils have been wound. The first winding packs of the toroidal field magnets are complete, as are the first casings, which have been verified to meet the high tolerances required. The first vacuum vessel sector is near completion and demonstrated to meet strict tolerances. The heating and current drive systems (neutral beams, electron cyclotron heating and ion cyclotron heating) are in the final design phase. The sequence of ITER operation from First Plasma to the achievement of the Q = 10 and Q = 5 project goals has been adapted to the Staged Approach to construction, a stepwise installation of all systems. The ITER Research Plan has been revised in 2017 to be consistent with the systems available in each phase. Physics studies focus on the disruption mitigation system, design of the ITER tungsten divertor, and modelling of ITER plasma scenarios. Modelling concentrates on the initial phases of the Research Plan and on the Q = 10 scenario, especially plasma termination.

Magnetic Field Mapping of the CLAS12 Torus—A Comparative Study Between the Engineering Model and Measurements at JLab

This paper provides an overview of the magnetic field measurement and subsequent electromagnetic re-modeling of the CLAS12 torus during the commissioning of the magnet in the fall of 2016. The CLAS12 detector in Hall B is part of the 12 GeV Accelerator Upgrade project at Jefferson Lab. The torus magnet allows precise determination of particle momenta within a cone ~ (5°-40°) in the forward direction. The ability to do this requires that we know the ∫B·dl of the torus to within an accuracy of 0.5% or better. To achieve this, an accurate model of the field along the particle path is required. The TOSCA code is used to generate a full three-dimensional (3-D) simulation of the magnetic envelope of the magnet as designed. Experimentally, the actual magnetic field within the magnet was surveyed to confirm the model design and to measure the deviation from the ideal case. The magnetic field deviations are attributed to manufacturing variability and assembly tolerances. A final model was created with allowances for these deviations guided by the survey data to create a more precise field integral model, which greatly improves the momentum resolution capability, allowing it to deliver the required specifications.

A Novel Open Drum Shaped Ultrasensitive Permittivity and Permeability Sensor Based on Electric–Magnetic Toroidal Dipole

A novel open drum shaped cavity (ODSC) is employed to estimate the variation of the dielectric and magnetic properties of materials. Compared with the conventional resonant mode excited by normal multipoles, it has the following remarkable property, i.e., concentrating energy. Almost all time-varying electric and magnetic fields are confined inside the ODSC and has high quality factor Q = 573.3. The resonant frequency is ultrasensitive to permittivity and permeability perturbations. The sensitivity is as high as 400 MHz, which is much higher than that in the published literatures. The properties of the target material are estimated by the amount of frequency shift of reflection coefficient S 11. The operation principle of the proposed sensor is initially illustrated by simulations, and then, measurements are performed to show the validity of the proposed procedure. This ultrasensitive sensor can be applied in accurate monitoring variations of permittivity or permeability of liquids, gases, and solids, such as avoiding overuse of cooking oil and qualified dried milk composition.

Identification of the Postulated Initiating Events of Accidents Occurring in a Toroidal Field Magnet of the EU DEMO

The design of the European Union (EU) DEMO reactor magnet system, currently ongoing within the EUROfusion consortium, will take advantage of the know-how developed during the design and manufacturing of ITER magnets; however, DEMO will suffer some new, more severe challenges, e.g., larger tritium inventory and higher neutron fluence, both having an impact on safety functions accomplished, among the other systems, also by the magnets. For these reasons, and in view of the need to demonstrate a high availability of the reactor (aimed at electricity production), a new, more systematic assessment of the system safety is required. As a contribution in this direction, the initiating events (IEs) of the most critical accident sequences in the EU DEMO magnet system (with special reference to the toroidal field magnets) are identified here, adopting first a functional analysis and then a failure mode, effects, and criticality analysis. In particular, the following are provided: (1) the EU DEMO magnet system is subdivided into functionally independent subsystems and components (e.g., the magnets, their cooling circuits, and their power supply system); (2) the relevant failure modes of each subsystem are systematically identified, together with the corresponding causes and consequences; (3) a list of IEs is compiled, leading to scenarios that may compromise the magnet safety and availability. Finally, the so-called postulated IEs are selected as the most challenging IEs for the safety of the magnet system. This analysis initializes a path leading to a risk-informed design, i.e., the identification of safety issues that could be addressed at the design level instead of introducing expensive mitigation measures after the design completion.

Charge Transfer Effect under Odd-Parity Crystalline Electric Field: Divergence of Magnetic Toroidal Fluctuation in β-YbAlB4

A novel property of the quantum critical heavy fermion superconductor $\beta$-YbAlB$_4$ is revealed theoretically. By analyzing the crystalline electronic field (CEF) on the basis of the hybridization picture, odd parity CEF is shown to exist because of sevenfold configuration of B atoms around Yb, which breaks the local inversion symmetry. This allows onsite admixture of 4f and 5d wavefunctions with a pure imaginary coefficient, giving rise to the magnetic toroidal (MT) degree of freedom. By constructing a realistic minimal model for $\beta$-YbAlB$_4$, we show that onsite 4f-5d Coulomb repulsion drives charge transfer between the 4f and 5d states at Yb, which makes the MT fluctuation as well as the electric dipole fluctuation diverge simultaneously with the critical Yb-valence fluctuation at the quantum critical point of the valence transition.

Atomic-Scale Magnetic Toroidal Dipole under Odd-Parity Hybridization

Magnetic toroidal dipole (MTD) is one of a fundamental constituent to induce magneto-electric effects in the absence of both spatial inversion and time-reversal symmetries. We report on a microscopic investigation of the atomic-scale MTD in solids by taking into account the orbital degree of freedom with a different parity. We construct an effective two-orbital $d$-$f$ tight-binding model on a polar tetragonal system for describing the atomic-scale MTD, which are obtained by incorporating the atomic spin-orbit coupling and odd-parity hybridization. The effective model exhibits two types of the MTDs: in-plane $x, y$ components activated through spontaneous ferromagnetic ordering or external magnetic field and an out-of-plane $z$ component by a spontaneous odd-parity hybridization without spin moments. We show that the intra-orbital (inter-orbital) Coulomb interaction in multi-orbital systems plays an important role in stabilizing the in-plane (out-of-plane) MTD orderings. We also examine the magneto-electric effect under each MTD ordering by calculating a linear response tensor. We show that the odd-parity hybridization enhances the magneto-electric effect for the in-plane MTDs, while it suppresses that for the out-of-plane MTD.

Compact steady-state tokamak performance dependence on magnet and core physics limits.

Compact tokamak fusion reactors using advanced high-temperature superconducting magnets for the toroidal field coils have received considerable recent attention due to the promise of more compact devices and more economical fusion energy development. Facilities with combined fusion nuclear science and Pilot Plant missions to provide both the nuclear environment needed to develop fusion materials and components while also potentially achieving sufficient fusion performance to generate modest net electrical power are considered. The performance of the tokamak fusion system is assessed using a range of core physics and toroidal field magnet performance constraints to better understand which parameters most strongly influence the achievable fusion performance.This article is part of a discussion meeting issue ‘Fusion energy using tokamaks: can development be accelerated?’.

Favourable and Unfavourable Effect of Homogeneous Static Magnetic Field on Germination of Zea mays L (Maize) Seeds

The effect of homogeneous static magnetic stimulation on Zea mays L. (maize) seeds and its potential utility as a tool in biotechnological development for the improvement of maize seeds was studied. The values of magnetic flux density that influenced the biological development of some plant species of the Poaceae family were determined from a literature review. ICA V-305 variety corn seeds were exposed to seven values of magnetic flux density between 50.0 mT and 250.0 mT, with homogeneity of 98.4% and at (1.0, 3.0, 5.0 and 7.0) min exposure times. The mean germination time (MGT), index of germination speed (VGer) and germination rate (Gmax) were evaluated as responses. The magnetic flux density of 50.0 mT with a one-minute exposure time recorded the largest reduction (12.4%) in the MGT while the germination rate for the same treatment increased by 17.4% with respect to the control. No significant effects of the magnetic treatment were recorded for the Gm&amp;aacute;x . The magnetic treatment of seeds with homogeneous static fields does not have as favourable a response as the treatments with fields with magnetic gradients, that is to say, using toroidal magnets.

Recent developments in single-molecule toroics.

Single-molecule toroics (SMTs) are defined as bi-stable molecules with a toroidal magnetic state, which have broad application prospects in quantum computing and information storage, and can also be used as multiferroic materials with a magneto-electric coupling effect. Since the first observation of the SMT behavior of typical Dy3 molecules, great progress has been made in the field of SMTs. In this Perspective, we provide an up-to-date overview of the emerging SMT architectures reported in recent years. Accordingly, thirteen representative examples with toroidal magnetization moments are discussed in order to elucidate the synthetic strategy to design SMT complexes and the factors dictating the arrangement of toroidal magnetic moments, and ultimately enlighten the study of SMTs with enhanced toroidal magnetization.