Component Of Magnetic Field Research Articles

Classification and Distribution of the Dayside Ion Upflows Associated with Auroral Particle Precipitation

Two important phenomena of the solar wind–magnetosphere–ionosphere coupling are auroral particle precipitation and the formation of ions flowing upward from the ionosphere. They have opposite transport directions of energy and substance. Based on the observations of particle precipitation and ion drift from the DMSP F13 satellite in January and July 2005, the ionospheric ion upflows in dayside auroral oval (0600–1800 MLT) can be divided into five types according to the velocity of ion upflows and the spectrum characteristics of auroral particle precipitation, and the distribution for different types of ion upflows is studied. The results show that the ion upflows mainly occur in the geomagnetic latitude (MLAT) range of 70–80°.The main magnetospheric source region of ion upflows (type A and D) caused by the accelerated electron (mainly the soft electron) corresponds to Low Latitude Boundary Layer (LLBL) and Cusp, and ion upflows of type B and C (related to the process of ambipolar diffusion caused by electron acceleration) mainly occur in LLBL and Boundary Plasma Sheet (BPS), while ion upflows of type E without electron acceleration mainly occur in the central plasma sheet (CPS).The dawn–dusk asymmetry is obvious in the winter season, with the ion upflows mainly occurring on the dawn/dusk side ionosphere. However, the ion upflows in summer mainly occur at the magnetic noon, with a symmetric distribution centered at the magnetic noon. The occurrence of ion upflow in winter is significantly higher than that in summer, and it is significantly enhanced during the period of moderate geomagnetic activity. The upward region expands to the lower latitude when the geomagnetic activity is enhanced. The effect of interplanetary magnetic field (IMF) components has also been studied in this paper. When IMF Bx is negative, the upflow occurrence increases in the region of 1500–1800 MLT and 0600–0900 MLT, with the MLAT range below 70°. The direction of IMF By may lead to the high-incidence area reverse at the prenoon or postnoon region. The occurrence of ion upflows with the MLAT range below 75° increases significantly when IMF is southward. Type A ion upflow has the highest velocity of ion upflows, followed by type E, and type D has the lowest. The average velocity of ion upflows in winter is significantly higher than that in summer.

Scattering characteristics of electrically large arbitrarily shaped targets illuminated by an off-axis vortex electromagnetic beam

For the application of vortex electromagnetic (EM) beams in practical detection scenes, the scattering characteristics of electrically large arbitrarily shaped targets illuminated by an off-axis Laguerre–Gaussian (LG) vortex beam are investigated and compared to the on-axis incidence case. The vector potential method is used to extract the electric and magnetic field components of the LG beam in different polarization states. The physical optics algorithm is adopted to calculate the scattering fields of four typical targets with the shape of a sphere, NASA almond, blunt cone, and blade model. The results revealed that as the beam center offset and the topological charge of the incident vortex beam increase, the scattering field distorts, and the obvious orbital angular momentum (OAM) spectrum mixing occurs. In addition, OAM spectrum aliasing occurs for asymmetric targets, even at on-axis incidence. These results elucidate the mechanism of vortex EM scattering and provide a reference for applying vortex beams for target detection and recognition.

Angle-dependent Magnetoresistance of an Ordered Bose Glass of Vortices in YBa2Cu3O7-δ Thin Films with a Periodic Pinning Lattice

The competition between intrinsic disorder in superconducting YBa2Cu3O7−δ (YBCO) thin films and an ultradense triangular lattice of cylindrical pinning centers spaced at 30 nm intervals results in an ordered Bose glass phase of vortices. The samples were created by scanning the focused beam of a helium-ion microscope over the surface of the YBCO thin film to form columns of point defects where superconductivity was locally suppressed. The voltage–current isotherms reveal critical behavior and scale in the vicinity of the second-order glass transition. The latter exhibits a distinct peak in melting temperature (Tg) vs. applied magnetic field (Ba) at the magnetic commensurability field, along with a sharp rise in the lifetimes of glassy fluctuations. Angle-dependent magnetoresistance measurements in constant-Lorentz-force geometry unveil a strong increase in anisotropy compared to a pristine reference film where the density of vortices matches that of the columnar defects. The pinning is therefore, dominated by the magnetic-field component parallel to the columnar defects, exposing its one-dimensional character. These results support the idea of an ordered Bose glass phase.

A Broadband Multicomponent Magnetic Probe With Improved Electric-Field Suppression Performance

This article presents a broadband multicomponent magnetic probe with improved electric-field suppression performance. First, two orthogonal sensing loops were introduced into a magnetic probe to capture simultaneously two orthogonal magnetic-field components. Then, a via array and fence were used to adjust impedance matching and restrain unwanted electromagnetic modes, respectively. In addition, shielding vias were arranged on the upper part of these loops to improve electric-field suppression performance. As a result, high electric-field suppression was obtained in the composite probe using shielding vias. Finally, the proposed magnetic probe was simulated, fabricated, and tested to verify the design’s rationality.

Detecting Weak Physical Signal from Noise: A Machine-Learning Approach with Applications to Magnetic-Anomaly-Guided Navigation

Detecting a weak physical signal immersed in overwhelming noises entails separating the two, a task for which machine learning is naturally suited. In principle, such a signal is generated by a nonlinear dynamical system of intrinsically high dimension for which a mathematical model is not available, rendering unsuitable traditional linear or nonlinear state-estimation methods that require an accurate system model (e.g., extended Kalman filters). We exploit the architectures of reservoir computing and feed-forward neural networks (FNNs) with time-delayed inputs to solve the weak-signal-detection problem. As a prototypical example, we apply the machine-learning schemes to Earth's magnetic anomaly field-based navigation. In particular, the time series are collected from the interior of the cockpit of a flying aircraft during different maneuvering phases, where the overwhelmingly strong noise background is the result of other components of Earth's magnetic field and the fields generated by the electronic devices in the cockpit. We demonstrate that, when combined with the traditional Tolles-Lawson model for Earth's magnetic field, the articulated machine-learning schemes are effective for accurately detecting the weak anomaly field from the noisy time series. The schemes can be applied to detecting weak signals in other domains of science and engineering.

Double Superposed Epoch Analysis of Geomagnetic Storms and Corresponding Solar Wind and IMF in Solar Cycles 23 and 24

AbstractThe weakest solar cycle 24 (SC24, 2010–2019) in 100 years was 1/3rd less active compared to the previous solar cycle 23 (SC23, 1996–2009). We identify 135 and 61 ICME (interplanetary coronal mass ejection) driven clear geomagnetic storms (DstMin ≤ −50 nT) in SC23 and SC24, respectively, giving a reduction of 55% storms in SC24, and present the double superposed epoch analysis (DSEA) of the storms/activities in SC23 and SC24 using the Dst, symmetric H (SymH), Kp and AE indices. The DSEA method for the corresponding solar wind velocity V, north‐south component of the interplanetary magnetic field (IMF Bz) and the product VBz are also presented. Compared to SC23, the maximum storm/activity intensity in SC24 reduces by 52%, 12%, and 45% at low, mid and high latitudes and the corresponding maxima in ‐VBz, V, and ‐Bz reduce by 39%, 17%, and 38%, respectively. The epoch average storm/activity intensity reduces by 27%, 11%, and 4% at low, mid and high latitudes and average maxima in ‐VBz, V, and ‐Bz reduce by 24%, 14%, and 13%, respectively. The results seem to reveal that the average reduction in the main driver ‐VBz (∼24%) might have caused nearly the same and equal average storm/activity intensity reductions in all latitudes (∼25%), though the irregular nature of the AE index makes the reduction very small (4%) at high latitudes, and small (∼11%) at mid latitudes mainly due to the small (0–9) quasi logarithmic scale of the Kp index.

Effects of Winding Angle on Losses of CORC Cable—A Numerical Study

The conductor-on-round-core (CORC) cable made of high-temperature superconductors coated conductors possess advantages in current carrying capability, mechanical strength, and flexibility. Its relatively complicated structure raises interests in the losses during operation and the related stability. In this article, we investigated the effects of winding angle on CORC losses under various excitation conditions. The results show that the ac loss is positively related to the winding angle owning to the increased magnetic field component perpendicular to the tape which will reduce its critical current density ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$J_{c}$</tex-math></inline-formula> ). CORC cables with an even number of layers wound in reverse show a significant reduction of stray fields and hence diminish the ac loss. The magnetization loss depends on the magnitude of the external field. It is positively correlated with the winding angle under low fields and approaches a constant under high fields. The conclusions indicate that from the perspective of losses, a small winding angle is suggested which can be used as a reference for the commercialization and practical manufacturing of CORC cables.

Auroral, Ionospheric and Ground Magnetic Signatures of Magnetopause Surface Modes

AbstractSurface waves on Earth's magnetopause have a controlling effect upon global magnetospheric dynamics. Since spacecraft provide sparse in situ observation points, remote sensing these modes using ground‐based instruments in the polar regions is desirable. However, many open conceptual questions on the expected signatures remain. Therefore, we provide predictions of key qualitative features expected in auroral, ionospheric, and ground magnetic observations through both magnetohydrodynamic theory and a global coupled magnetosphere‐ionosphere simulation of a magnetopause surface eigenmode. These show monochromatic oscillatory field‐aligned currents (FACs), due to both the surface mode and its non‐resonant Alfvén coupling, are present throughout the magnetosphere. The currents peak in amplitude at the equatorward edge of the magnetopause boundary layer, not the open‐closed boundary as previously thought. They also exhibit slow poleward phase motion rather than being purely evanescent. We suggest the upward FAC perturbations may result in periodic auroral brightenings. In the ionosphere, convection vortices circulate the poleward moving FAC structures. Finally, surface mode signals are predicted in the ground magnetic field, with ionospheric Hall currents rotating perturbations by approximately (but not exactly) 90° compared to the magnetosphere. Thus typical dayside magnetopause surface modes should be strongest in the East‐West ground magnetic field component. Overall, all ground‐based signatures of the magnetopause surface mode are predicted to have the same frequency across L‐shells, amplitudes that maximize near the magnetopause's equatorward edge, and larger latitudinal scales than for field line resonance. Implications in terms of ionospheric Joule heating and geomagnetically induced currents are discussed.

The Ionospheric Dynamics of the African Sector Responding to a Severe Geomagnetic Storm; the Storm of 3–5 November 2021

AbstractThe sudden storm commencement (SSC) of 3 November 2021, a severe storm was detected through disturbances in magnetospheric and ring current systems at around 1942 UT. We used a daily variation of total electron content (TEC) from ground‐based GNSS stations, ionosonde parameters and modeled zonal and meridional wind velocities to study the ionospheric response over the African region by comparing storm and quiet time variations. The equatorial GNSS station of NKLG recorded initial positive storm effects around the time of SSC, of which these effects spread over the whole African region during the main phase with positive and negative storm effects during the main and recovery phases respectively. The two disturbances at the SSC and the main phase were caused by the penetrating electric field and traveling atmospheric disturbances respectively. The analysis of TIMED Global UltraViolet Imager images revealed storm time‐induced changes in thermospheric composition during the main phase which resulted in a differential ionospheric response with intense, moderate, and weak positive storm effects in northern, equatorial, and southern regions respectively. The horizontal magnetic field components show two signatures of prompt penetration electric field that suppressed the formation of the equatorial anomaly at SSC and enhanced positive storm effects in the equatorial region at the main phase, Therefore, the ionospheric response was due to the relative contributions of prompt penetration electric field effects and equatorward traveling disturbances which depended on storm onset time, past ionospheric state, and storm phase.

A Detailed Model of Magnetic Field Sources of the Earth’s Core Obtained by Solving the Inverse Problem of Magnetometry

Abstract —Magnetic field sources are sometimes approximated by magnetic dipoles or current loops. The usefulness of such approximations is not obvious at the initial stage of the study of objects. Investigating them in detail requires volumetric magnetic field sources. In this paper, they are represented by magnetized prisms. Such a model is valid due to the equivalence of current and magnetized objects. As there should be no real magnetization in the core, this property of a virtual prism to generate a magnetic field strength is referred to as virtual or effective magnetization (EM), which is determined for each prism by solving the inverse problem via the adaptive method. Initial data for solving the inverse problem are the Z vector components of the main magnetic field of the IGRF-2005 model in the geocentric coordinate system. Based on the effective magnetization and known formulas, the bulk current distribution, the bulk current density, and the magnetic moments of prisms of a two-layer core model are obtained. Their sum coincides with the magnetic moment of the virtual central dipole of the core, but, as many scientists assumed, the central dipole is not actually distinguished. At the same time, four significant inhomogeneities are identified in the core, which create the Canadian, Siberian-Asian, Australian, and negative South Atlantic global anomalies on the Earth’s surface. Based on the analysis of the results obtained, assumptions are made that the current generating the magnetic field is the motion of a positively weakly charged liquid of the core. Liquid motion is created by the rotation of the Earth and the decelerating gravitational forces of the Moon and the Sun. Arguments are given to support these assumptions. The results are illustrated in figures.

Dynamic resistance and total loss in small REBCO pancake and racetrack coils carrying DC currents under an AC magnetic field

In many high-temperature superconducting applications, REBCO (Rare-earth barium copper oxide) coils carry DC currents under AC magnetic fields, such as the field winding of rotating machines, linear synchronous motors and the electro-dynamic suspension system of maglev. In such operating conditions, REBCO coils generate AC loss—total loss which includes the magnetization loss due to the shielding currents, and the dynamic loss arising from dynamic resistance caused by the interaction of DC currents and AC magnetic fields. In this work, dynamic resistance and total loss in a small double pancake coil (DPC) and a small double racetrack coil (DRC) are investigated via experiments in the temperature range between 77 K and 65 K. The DC currents are varied from zero to 70% of the self-field critical currents of the REBCO coils, with AC magnetic fields up to 100 mT. The experimental results in the DPC are well supported by the finite element simulation results using 3D T-A formulation. Our results show that the critical current of the DRC is approximately 2%–5% higher than that of the DPC in the temperature range. For given experimental conditions, the magnetization loss in both coils is much greater than the dynamic loss. The dynamic loss and magnetization loss in the DRC are greater than those in the DPC, which we attribute to the large perpendicular magnetic field component in the straight sections of the DRC.

Linking the interiors and surfaces of magnetic stars

ABSTRACTStrong magnetic fields are observed in a substantial fraction of upper main sequence stars and white dwarfs. Many such stars are observed to exhibit photometric modulations as the magnetic poles rotate in and out of view, which could be a consequence of magnetic perturbations to the star’s thermal structure. The magnetic pressure is typically larger than the gas pressure at the star’s photosphere, but much smaller than the gas pressure in the star’s interior, so the expected surface flux perturbations are not clear. We compute magnetically perturbed stellar structures of young $3 \, \mathrm{M}_\odot$ stars that are in both hydrostatic and thermal equilibrium, and which contain both poloidal and toroidal components of a dipolar magnetic field as expected for stable fossil fields. This provides semi-analytical models of such fields in baroclinic stably stratified regions. The star’s internal pressure, temperature, and flux perturbations can have a range of magnitudes, though we argue the most likely configurations exhibit flux perturbations much smaller than the ratio of surface magnetic pressure to surface gas pressure, but much larger than the ratio of surface magnetic pressure to central gas pressure. The magnetic pole is hotter than the equator in our models, but a cooler magnetic pole is possible depending on the magnetic field configuration. The expected flux variations for observed field strengths are δL/L ≲ 10−6, much smaller than those observed in magnetic stars, suggesting that observed perturbations stem from changes to the emergent spectrum rather than changes to the bolometric flux.

Fast time-varying current triggering flux jumps of multi-filamentary Nb3Sn wire exposed to oblique magnetic field

Due to the oblique magnetic field and rapid time-varying current, the electromagnetic response and thermomagnetic instabilities of high-field superconducting dipole magnets are quite different from the solenoid coils. In this work, we theoretically investigate the flux jump of composite multi-filamentary Nb3Sn wire with high critical current density exposed to an oblique magnetic field and fast transport current. The thermomagnetic stability/instability regions are obtained with respect to flux creep factor and oblique ratios of magnetic field. It is found that the parallel component of the oblique magnetic field can suppress the flux jump. Unlike slow current, it is interesting to find that the fast variations of self-field by high ramp current can trigger flux jumps in Nb3Sn wire. The fast current triggering flux jumps can be tuned by the static oblique magnetic field. Furthermore, we demonstrate that current-like distribution is more likely to trigger quenches, while the magnetic field-like distribution is more likely to trigger flux jumps. The findings of this work are helpful for the optimization of the superconducting coils exposed to oblique magnetic field and fast time-varying current.

Vectorization of magneto-optical images of a in plane component of inhomogeneous magnetic fields

A method based on the magneto-optical Kerr effect is demonstrated, which makes it possible to quantitatively determine spatial dependences of the directions of an in-plane component of inhomogeneous magnetic field visualized by soft nanocrystalline films. The method consists in obtaining magneto-optical images of micromagnetic structures that are formed under the influence of an inhomogeneous field. Images in the longitudinal and transverse sensitivity of the Kerr effect are used to calculate the angular dependence of the directions of the unit vectors of this field under the assumption that the components of the field are proportional to the brightness of magneto-optical images. The field direction maps obtained in this way agree with model calculations for our magnets.

Solar Orbiter Data‐Model Comparison in Venus' Induced Magnetotail

AbstractWe investigate the structure of the Venusian magnetotail utilizing magnetic field and electron density measurements that cover a wide range of distances from the planet, from the first two Solar Orbiter Venus flybys. We examine the magnetic field components along the spacecraft trajectory up to 80 Venus radii down the tail. Even though the magnetic field behavior differs considerably between the two cases, we see extended electron density enhancements covering distances greater than ∼20 RV in both flybys. We compare the magnetic field measurements with a global hybrid model of the induced magnetosphere and magnetotail of Venus, to examine to what degree the observations can be understood with the simulation. The model upstream conditions are stationary and the solution encloses a large volume of 83 RV × 60 RV × 60 RV in which we look for spatial magnetic field and plasma variations. We rotate the simulation solution to describe different stationary upstream IMF clock angle cases with a 10° step and find the clock angle for which the agreement between observations and model is maximized along Solar Orbiter's trajectory in 1‐min steps. We find that in both flybys there is better agreement with the observations when we rotate the model for some intervals, while there are parts that cannot be well reproduced by the model irrespective of how we vary the IMF clock angle, suggesting the presence of non‐stationary features in the Venus‐solar wind interaction not accounted for in the hybrid model.

Comparison of the low-frequency characteristics of the model solar wind spiral magnetic cloud with observed disturbances

We presented the results of a comparison of the analytical study of the features of the radial distribution of MHD disturbances of the magnetic field components in the body of a model solar wind magnetic cloud with data on a real cloud recorded by a spacecraft. The analytical-numerical solution for perturbations is performed in a cylindrical coordinate system for a cloud represented by a force-free cylindrical tube with a helical magnetic field. The obtained general idea of the radial distribution of the magnetic field components in the MC body is consistent with the registered parameters of the magnetic field disturbances on the patrol spacecraft and is confirmed by an objective correlation analysis. Joint post-processing of the counting results and real data compared with them enhances the consistency, which indicates the adequacy of the applied MHD approach to the analysis of oscillations in the model body of the magnetic cloud.

Relationship between drift kinetics, gyrokinetics and magnetohydrodynamics in the long-wavelength limit

Gyrokinetic theories, even ‘global’ models, typically rely on a separation in scale (in perpendicular wavelength) between the fluctuations and the system scale. In such models direct simulation of system-scale dynamics like magnetohydrodynamic (MHD) motion is formally not consistent. Drift-kinetic theory, on the other hand, may be directly applied to model system-scale MHD-ordered behaviour. I review the long-wavelength limit of standard gyrokinetics and drift kinetics to present the relationships between these theories in an elementary fashion. This provides a pathway to global gyrokinetic modelling, resulting in an approach that is structurally similar to kinetic MHD, and I present dynamical equations for solving global field evolution in this framework. Departures from certain earlier global gyrokinetic theories include the appearance of magnetosonic (fast) modes, and the cross-coupling of the parallel and perpendicular currents with perpendicular and parallel magnetic field components. A periodic two-dimensional testcase is outlined as a benchmarking and implementation target, to help clarify practical aspects of these theories, with minimal complexity in terms of boundary conditions, and a proof-of-principle implementation of a field-solver is exhibited. To motivate this work, I first illustrate certain limitations of existing global gyrokinetic frameworks and directly identify how scale separation approximations lead to certain ‘missing’ system-scale field terms in global gyrokinetics, largely as a result of simplifications associated with the field representation in terms of $A_{\|}$ and $B_{\|}$ . As a result, the currents in the gyrokinetic Ampère's law resulting from a gyrokinetic equilibrium distribution do not match the currents implied by Ampère's law in a force-balance MHD equilibrium. I present a simple choice of equilibrium distribution function whose drift-kinetic currents are consistent with MHD currents; a specific Grad–Shafranov equilibrium is used to illustrate the size of the components of the parallel currents.

A Composite Probe Capable of Simultaneously Measuring Two Orthogonal Magnetic-Fields

In this brief, a broadband composite probe capable of simultaneously measuring two orthogonal magnetic-fields is proposed. A pair of center orthogonal detection loops are utilized to capture two orthogonal magnetic-field components ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$H_{x}$ </tex-math></inline-formula> and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$H_{y}$ </tex-math></inline-formula> ). In order to suppress undesired electromagnetic wave modes, two rows of via fences is placed on both sides of the probe. A pair of 2.92mm vertical compression-mount precision test connectors are used to achieve the good impedance matching. In order to verify the rationality of design, the composite probe is simulated, measured and studied. Compared with the conventional single-component probe, the proposed antenna has a unique advantage in simultaneously measuring two orthogonal magnetic-fields.

An Ultrawideband Differential Magnetic-Field Probe for Near-Field Scanning

In this study, a differential magnetic-field probe capable of measuring two orthogonal magnetic-field components is developed. Different from conventional single-component magnetic-field probes with a detection loop, the proposed probe consists of two orthogonal detection loops and a short-circuit point. Two orthogonal induced loops are used to sense the orthogonal magnetic-field components ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${H} _{y}$ </tex-math></inline-formula> and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${H} _{x}$ </tex-math></inline-formula> ). In addition, many grounded vias are inserted into the probe to suppress unwanted electromagnetic modes. To prove the design accuracy, the presented probe is simulated, measured, and analyzed. It is observed that the working frequency of the probe is 1 MHz–20 GHz.

Modeling the Magnetic Field of the Inner Corona in a Radially Expanding Solar Wind

The magnetic field in the interplanetary medium is formed by the action of magnetic field sources on the photosphere of the Sun and currents in the expanding atmosphere of the Sun and the solar wind. In turn, the high-speed plasma flow changes the configuration of the magnetic field lines. The problem of determining the parameters of the magnetic field near the Sun is thus a three-dimensional problem of the interaction of the magnetic field and the plasma of the solar wind. We present analytical expressions for calculating the total magnetic field vector B→(r, θ, ϕ) (in spherical coordinates) for a radially expanding solar wind flow of finite conductivity. The parameters of the solar wind are given in the form of a dimensionless magnetic Reynolds number given as an arbitrary function of the radius, r: Rm = rσμv=ξ(r), where σ, μ, and v denote, respectively, the conductivity, magnetic permeability, and velocity of the solar wind. The solution for the magnetic field components is obtained in the form of a decomposition in spherical functions and a radial part depending on the distance from the Sun. Examples of calculations of the configuration of magnetic fields and structures of the solar corona for the solar eclipse of 21 August 2017 are given.