Magnetic Field Generation Research Articles

Mechanical behavior of HTS tapes in highly flexible REBCO cable under torsional and tensile loads

Abstract Different cables composed of high-temperature superconducting (HTS) tapes (REBCO) have been developed for the generation of high magnetic fields and the transmission of large currents. Among the different HTS cables, the conductor on round core (CORC®) cable has become a promising candidate structure. In order to improve the flexibility of CORC® cable, a new kind of cable called HFRC (highly flexible REBCO cable) has been proposed, which has a similar configuration to CORC® cable. During the production of HFRC, REBCO tapes are wound on the surface of a spiral tube layer by layer. Compared to the solid core of traditional CORC® cable, the spiral tube is more prone to complex deformation under external loads, which results in special characteristics of REBCO tapes. In this paper, we analyze the deformation processes of spiral tubes under tension or torsion. Based on the geometrical relationship between the tapes and the cable core, the strain in REBCO tapes is predicted. Finite element models of HFRC/traditional CORC-like cable are built and verified by experiments. Through simulations, the variation of the strain and local creases of the tapes with the design parameters of the core is investigated. Relevant findings provide a reference for the structural optimization of HFRC.

Influence of oxygen on electronic correlation and transport in iron in the Earth’s outer core

Knowing the transport properties of iron at the Earth’s core conditions is essential for the geophysical modeling of Earth’s magnetic field generation. Besides by extreme pressures and temperatures (which cause scattering by thermal disorder to dominate), transport may be also influenced by the presence of light elements and electron-electron scattering. We used a combination of molecular dynamics, density functional theory, and dynamical mean-field theory methods to examine the impact of oxygen impurities on the electronic correlations and transport in the Earth’s liquid outer core. We find electronic correlations to be moderately enhanced by oxygen admixture. At realistic 10 atomic% of oxygen, the thermal conductivity suppression by electronic correlations (about 20%) is of the same magnitude as that due to oxygen inclusion. Hence, both play an equally important role in reducing the conductivity and stabilizing the geodynamo. We also explain the reduction of Lorenz ratio in core matter.

Research on Magnetic Field Generator and Vibration Measurement Errors in the Development of Eco-friendly Vehicle Noise and Vibration

Research on Magnetic Field Generator and Vibration Measurement Errors in the Development of Eco-friendly Vehicle Noise and Vibration

Diamagnetic levitation of water realized with a simple device consisting of ordinary permanent magnets

Diamagnetic levitation is an appealing technique for levitating objects at room temperature without subjecting the sample to potentially damaging control fields, such as high-intensity laser light or sound pressure. However, owing to the extremely low magnetic susceptibility of diamagnetic materials, except for bismuth and graphite, diamagnetic levitation generally necessitates the use of exceptionally strong magnets, such as those found in world-class high-field facilities. This study simulated the magnetic field distribution in a narrow valley formed between two adjacent rectangular cuboid magnets with antiparallel magnetizations, at a spatial resolution of 5 μm. The simulations indicated the generation of a strong magnetic force field, B∂B/∂z(>40 000 T2/m), which could lift not only light organic compounds but also dense metallic compounds. Moreover, the addition of another pair of smaller sized magnets provided a local potential minimum that satisfied the conditions for non-contact levitation. Based on these results, a compact magnetic levitation system was developed by combining four small commercially available magnets. Experimental results showed that a water droplet of approximately 0.3 mm diameter was levitated. The experimental space was nearly sealed and highly resistant to external disturbances, such as vibrations, allowing the water to remain in a non-contact levitated state unless the operator intentionally shook the experimental table or directed airflow to displace the water away. The device is expected to facilitate various applications in materials science and fluid dynamics as well as promote preliminary ground-based research on space-related experiments designed to be conducted in microgravity environments.

FEATURES OF GENERATION OF SPONTANEOUS MAGNETIC FIELDS IN FULLY IONIZED PLASMA

In this paper, magnetic field generation in a fully ionized plasma is discussed both in the presence and absence of an external constant magnetic field. Considering the dependence of the transfer coefficients on the magnetic field, Braginsky's equations are applied to describe collective processes in plasma. Criteria for the formation of instabilities and, consequently, the generation of magnetic fields are obtained, taking into account convective heat transfer and thermomagnetic phenomena. We derive expressions for the growth rate of perturbations in the magnetic field and the temperature in the short-wave range.

Mass Transfer and MHD Free Convection Flow Across a Stretching Sheet with a Heat Source and Chemical Reaction

This work examines mass transfer and MHD free convective flow across a stretching sheet in the presence of a heat source and a chemical reaction. The sheet's stretching action propels the flow, while a magnetic field applied perpendicular to the flow direction influences it. The effects of gradients in temperature and concentration on buoyant forces are also taken into account. The continuity, momentum, energy, and concentration equations are among the coupled nonlinear partial differential equations that regulate the system. Similarity transformations are used to convert these equations into a system of ordinary differential equations, which are then numerically solved using bvp4c techniques. In this investigation, magnetic, buoyancy, chemical reaction rate, and heat source factors are the main parameters of interest. The outcomes show the influence of these parameters on the boundary layer's temperature, concentration, and velocity profiles. To quantify the mass transfer rate, heat transfer rate, and shear stress at the sheet surface, the skin friction coefficient, Nusselt number, and Sherwood number are calculated. By manipulating the magnetic field, chemical reactions, and heat generation, the work offers important new insights into how to best utilise MHD flows in industrial processes, such as polymer manufacturing, chemical reactors, and cooling systems.

Magnetic seed generation by plasma heat flux in accretion disks

Magnetic batteries are potential sources that may drive the generation of a seed magnetic field, even if this field is initially zero. These batteries can be the result of nonaligned thermodynamic gradients in plasmas, as well as of special and general-relativistic effects. So far, magnetic batteries have only been studied in ideal magnetized fluids. We studied the nonideal fluid effects introduced by the energy flux in the vortical dynamics of a magnetized plasma in curved space-time. We propose a novel mechanism for generating a heat-flux-driven magnetic seed within a simple accretion disk model around a Schwarzschild black hole. We used the 3+1 formalism for the splitting of the space-time metric into space-like and time-like components. We studied the vortical dynamics of a magnetized fluid with a heat flux in the Schwarzschild geometry in which thermodynamic and hydrodynamic quantities are only dependent on the radial coordinate. Assuming that the magnetic field is initially zero, we estimated the linear time evolution of the magnetic field due to the inclusion of nonideal fluid effects. When the thermodynamic and hydrodynamic quantities vary only radially, the effect of the coupling between the heat flux, the space-time curvature, and the fluid velocity acts as the primary driver for an initial linearly time-growing magnetic field. The plasma heat flux completely dominates the magnetic field generation at a specific distance from the black hole, where the fluid vorticity vanishes. This distance depends on the thermodynamical properties of the Keplerian plasma accretion disk. These properties control the strength of the nonideal effects in the generation of seed magnetic fields. We find that heat flux is the main driver of a seed magnetic field in black hole accretion disks if the geometry, plasma dynamics, and thermodynamics share the same axial symmetry. This suggests that nonideal fluid effects may play a major role in the magnetization of astrophysical plasmas.

On the onset of thermal convection in a rotating spherical shell with spatially heterogeneous heat source distribution

Thermal convection in rotating spherical shells effectively model the fluid motions occurring in molten cores of planetary interiors. In the Earth's outer core, such convective motions when subjected to spatial varying thermal buoyancy undergo characteristic modifications that fundamentally affect the consequent magnetic field generation. In addition to the extensively explored mechanism of boundary heat flux (BH) variations, the present study majorly focuses on a novel mechanism of heat source heterogeneity (SH)-driven buoyancy forcing, mimicking non-uniform secular cooling in the outer core. The direct effect of heat sources on the temporal evolution of temperature contrasts the heat flux control exerted by BH forcing. The most prominent difference is the capability of SH forcing to modulate the thermo-fluidic state in the entire shell while the BH-driven anomalies are limited to regions close to the outer boundary only. Dynamically, SH forcing is relatively more effective, with weaker heterogeneity causing transformations in the thermo-fluidic patterns analogous to stronger BH cases. Compared to the homogeneous case, SH leads to a reduction in onset threshold, localization of the convective instabilities, concentrated steady thermal winds, the dominance of anti-cyclonic axial helicity, and overall homogenization with smaller scaled spherical harmonic heterogeneity patterns. Moreover, a novel phenomenon of dual onset is observed for the SH configuration only, marking distinctive transitions in the convective instability features with larger variations. Finally, the effect of SH on the thermal state at the boundaries indicate the plausibility of strong core–mantle and outer–inner core interactions with significant geophysical implications.

Stable Stratification of the Helium Rain Layer Yields Vastly Different Interiors and Magnetic Fields for Jupiter and Saturn

At sufficiently high pressures (∼Mbar) and low temperatures (∼103–104 K), hydrogen and helium become partly immiscible. Interpretations of Jupiter’s and Saturn’s magnetic fields favor the existence of a statically stable layer near the Mbar pressure level. From experimental and computational data for the hydrogen–helium phase diagram, we find that moist convection and diffusive convection are inhibited, implying a stable helium rain layer in both Jupiter and Saturn. However, we find a significant difference in terms of structure and evolution: in Jupiter, helium settling leads to a stable yet superadiabatic temperature gradient that is limited by conductive heat transport. The phase separation region should extend only a few tens of kilometers, instead of thousands in current-day models, and be characterized by a sharp increase of the temperature of about 500 K for standard phase separation diagrams. In Saturn, helium rains occur much deeper, implying a larger helium flux relative to planetary mass. We find that the significant latent heat associated with helium condensation implies that a large fraction, perhaps close to 100%, of the planet’s intrinsic heat flux may be locally transported by the sinking helium droplets. This implies that Saturn may possess a much more extended helium rain region. This also accounts, at least qualitatively, for the differences in strength and characteristics of the magnetic fields of the two planets. Dedicated models of magnetic field generation in both planets may offer observational constraints to further refine these findings.

Unravelling sub-stellar magnetospheres

At the sub-stellar boundary, signatures of magnetic fields begin to manifest at radio wavelengths, analogous to the auroral emission of the magnetised solar system planets. This emission provides a singular avenue for measuring magnetic fields at planetary scales in extrasolar systems. So far, exoplanets have eluded detection at radio wavelengths. However, ultracool dwarfs (UCDs), their higher mass counterparts, have been detected for over two decades in the radio. Given their similar characteristics to massive exoplanets, UCDs are ideal targets to bridge our understanding of magnetic field generation from stars to planets. In this work, we develop a new tomographic technique for inverting both the viewing angle and large-scale magnetic field structure of UCDs from observations of coherent radio bursts. We apply our methodology to the nearby T8 dwarf WISE J062309.94-045624.6 (J0623) which was recently detected at radio wavelengths, and show that it is likely viewed pole-on. We also find that J0623’s rotation and magnetic axes are misaligned significantly, reminiscent of Uranus and Neptune, and show that it may be undergoing a magnetic cycle with a period exceeding 6 months in duration. These findings demonstrate that our method is a robust new tool for studying magnetic fields on planetary-mass objects. With the advent of next-generation low-frequency radio facilities, the methods presented here could facilitate the characterisation of exoplanetary magnetospheres for the first time.

Magnetized wastewater treatment using Williamson’s triple hybrid nanofluid with variable viscosity and internal heat generation on a permeable surface

PurposeTry to find a way to treat wastewater and achieve its purification from suspended waste, which was removed by examining the magneto-Williamson fluid on a horizontal cylindrical tube while taking advantage of solar radiation and nanotechnology.Design/methodology/approachThe effect of Cattaneo–Christoph law of heat transfer, solar radiation, oblique magnetic field, porosity and internal heat generation on the flow was studied. The control system was solved by the numerical technique of Chebyshev pseudospectrum (CPS) with the help of the program MATHEMATICA 12. The tables comparing the published data results with the existing numerical calculation match exactly.FindingsThe tables comparing the published data results with the existing numerical calculation match exactly. The current simulation results indicate that when using variable viscosity, the Nusselt number and surface friction decrease significantly compared to their value in the case of constant viscosity, and variable viscosity has a significant effect on flow, which reduces speed. Curves and increasing temperature profiles.Originality/valueDeveloping a theoretical framework for the problem of sewage turbidity in a healthier and less costly way, by studying the flow of Williamson fluid with variable viscosity (to describe the intensity of sewage turbidity) on a horizontal cylindrical tube, and taking advantage of nanotechnology, solar radiation, Christoph’s thermal law and internal heat generation to reach water free of impurities. Inclined magnetic force and porous force were used, both of which played an effective role in the purification process.

Generation of 10 kT axial magnetic fields using multiple conventional laser beams: A sensitivity study for kJ PW-class laser facilities

Strong multi-kilotesla magnetic fields have various applications in high-energy density science and laboratory astrophysics, but they are not readily available. In our previous work [Y. Shi et al., Phys. Rev. Lett. 130, 155101 (2023)], we developed a novel approach for generating such fields using multiple conventional laser beams with a twist in the pointing direction. This method is particularly well-suited for multi-kilojoule petawatt-class laser systems like SG-II UP, which are designed with multiple linearly polarized beamlets. Utilizing three-dimensional kinetic particle-in-cell simulations, we examine critical factors for a proof-of-principle experiment, such as laser polarization, relative pulse delay, phase offset, pointing stability, and target configuration, and their impact on magnetic field generation. Our general conclusion is that the approach is very robust and can be realized under a wide range of laser parameters and plasma conditions. We also provide an in-depth analysis of the axial magnetic field configuration, azimuthal electron current, and electron and ion orbital angular momentum densities. Supported by a simple model, our analysis shows that the axial magnetic field decays owing to the expansion of hot electrons.

Primordial magnetogenesis in a bouncing model with dark energy

We investigate primordial magnetogenesis within a quantum bouncing model driven by a scalar field, focusing on various non-minimal couplings between the electromagnetic field and the scalar field. We test three cases: no coupling, a Cauchy coupling with gradual decay, and a Gaussian coupling with rapid fall-off. By exploring these scenarios, we assess a wide range of coupling strengths across different scales. The scalar field, with an exponential potential, behaves as pressureless matter in the asymptotic past of the contracting phase, as stiff matter around the bounce, and as dark energy during the expanding phase. Our findings reveal that, among the tested cases, only the Gaussian coupling can explain the generation of primordial magnetic fields on cosmological scales.

A concise 40 T pulse magnet for condensed matter experiments

There is a growing interest in using pulsed high magnetic field as a controlling parameter of physical phenomena in various scientific disciplines, such as condensed matter physics, particle physics, plasma physics, chemistry, and biological studies. We devised a concise and portable pulsed magnetic field generator that produces a 40 T field with a pulse duration of 2 ms. It is assembled using only off-the-shelf components and a homemade coil that leverages small computers, Raspberry Pi, and Python codes. It allows for straightforward modification for general purposes. As working examples, we show representative applications in condensed matter experiments of magnetoresistance, magnetization, and magnetostriction measurements for graphite, NdNi2P2, and NdCo2P2, respectively, with the maximum magnetic field of 41 T and the lowest temperature of 4.2 K.

Planetary Interior Configuration Control on Thermal Evolution and Geological History

AbstractThe terrestrial planetary bodies display a wide variety of surface expressions and histories of volcanic and tectonic, and magnetic activity, even those planets with apparently similar dominant modes of heat transport (e.g., conductive on Mercury, the Moon, and Mars). Each body also experienced differentiation in its earliest evolution, which may have led to density‐stabilized layering in its mantle and a heterogenous distribution of heat‐producing elements (HPE). We explore the hypothesis that mantle structure exerts an important control on the occurrence and timing of geological processes such as volcanism and tectonism. We numerically investigate the behavior of an idealized model of a planetary body where HPE are assumed to be sequestered in a stabilized layer at the top or bottom of the mantle. We find that the mantle structure alters the patterns of heat flow at the boundaries of major heat reservoirs: The mantle and core. This modulates the way in which heat production influences geological processes. In the model, the mantle structure is a dominant control on the relative timing of fundamental processes such as volcanism, magnetic field generation, and expansion/contraction, the record of which may be observable on planetary body surfaces. We suggest that Mercury exhibits characteristics of shallow sequestration of HPE and that Mars exhibits characteristics of deep sequestration.

Solar internetwork magnetic fields: Statistical comparison between observations and MHD simulations

Context. Although the magnetic fields in the quiet Sun account for the majority of the magnetic energy in the solar photosphere, inferring their exact spatial distribution, origin, and evolution poses an important challenge because the signals lie at the limit of today’s instrumental precision. This severely hinders and biases our interpretations, which are mostly made through nonlinear model-fitting approaches. Aims. Our goal is to directly compare simulated and observed polarization signals in the Fe I 6301 Å and 6302 Å spectral lines in the very quiet Sun, the so-called solar internetwork (IN). This way, we aim to constrain the mechanism responsible for the generation of the quiet Sun magnetism while avoiding the biases that plague other diagnostic methods. Methods. We used three different three-dimensional radiative magneto-hydrodynamic simulations representing different scenarios of magnetic field generation in the internetwork: small-scale dynamo, decay of active regions, and horizontal flux emergence. We synthesized Stokes profiles at different viewing angles and degraded them according to the instrumental specifications of the spectro-polarimeter (SP) on board the Hinode satellite. Finally, we statistically compared the simulated spectra to the Hinode/SOT/SP observations at the appropriate viewing angles. Results. Of the three simulations, the small-scale dynamo best reproduced the statistical properties of the observed polarization signals. This is especially prominent for the disk center viewing geometry, where the agreement is excellent. Moving toward more inclined lines of sight, the agreement worsens slightly. Conclusions The agreement between the small-scale dynamo simulation and observations at the disk center suggests that small-scale dynamo action plays an important role in the generation of quiet Sun magnetism. However, the magnetic field around 50 km above the continuum layer in this simulation does not reproduce observations as well as at the very base of the photosphere.

Design and Optimization of a Magnetic Field Generator for Magnetic Particle Imaging with Soft Magnetic Materials

Design and Optimization of a Magnetic Field Generator for Magnetic Particle Imaging with Soft Magnetic Materials

Mean field responses in disordered systems: an example from nonlinear MHD

Understanding the generation of large-scale magnetic fields and flows in magnetohydro-dynamical (MHD) turbulence remains one of the most challenging problems in astrophysical fluid dynamics. Although much work has been done on the kinematic generation of large-scale magnetic fields by turbulence, relatively little attention has been paid to the much more difficult problem in which fields and flows interact on an equal footing. The aim is to find conditions for long-wavelength instabilities of stationary MHD states. Here, we first revisit the formal exposition of the long-wavelength linear instability theory, showing how long-wavelength perturbations are governed by four mean field tensors; we then show how these tensors may be calculated explicitly under the ‘short-sudden’ approximation for the turbulence. For MHD states with relatively little disorder, the linear theory works well: average quantities can be readily calculated, and stability to long-wavelength perturbations determined. However, for disordered basic states, linear perturbations can grow without bound and the purely linear theory, as formulated, cannot be applied. We then address the question of whether there is a linear response for sufficiently weak mean fields and flows in a dynamical (nonlinear) evolution, where perturbations are guaranteed to be bounded. As a preliminary study, we first address the nature of the response in a series of one-dimensional maps. For the full MHD problem, we show that in certain circumstances, there is a clear linear response; however, in others, mean quantities – and hence the nature of the response – can be difficult to calculate.

Investigation on Melting Curves and Phase Diagrams for CaO3 Using Deep Learning Potentials.

Melting in the deep rocky parts of planets plays an important role in geological processes such as planet formation, seismicity, magnetic field generation, thermal convection, and crustal evolution. Such processes are the key way to understanding the dynamics of planetary interiors and the history as well as mechanisms of planetary evolution. We herein investigate the melting curves and pressure-temperature (P-T)-phase diagrams for CaO3, a candidate mineral for the lower mantle, by means of the deep learning potential model. Using first-principles, molecular dynamics, and quasi-harmonic approximation, the reliability of the deep learning potential model is verified by calculating the high-temperature and high-pressure equations of state and phase transition pressures for the orthorhombic and tetragonal structures of CaO3 described by space groups Aea2 and P4̅21m, respectively. The melting temperatures of 975, 850, and 755 K at zero pressure are obtained by the single-phase, void, and two-phase methods, respectively, and their melting temperatures are analyzed by the radial distribution function and mean-square displacement to analyze the melting process. Finally, the melting phase diagrams of CaO3 at 0-135 GPa were obtained by the two-phase method.

Strong magnetic actuation system with enhanced field articulation through stacks of individually addressed coils

Miniaturization of medical tools promises to revolutionize surgery by reducing tissue trauma and accelerating recovery. Magnetic untethered devices, with their ability to access hard-to-reach areas without physical connections, emerge as potential candidates for such miniaturization. Despite the benefits, these miniature devices face challenges regarding force and torque outputs, restricting their ability to perform tasks requiring mechanical interactions such as tissue penetration and manipulation. To overcome magnetic actuation system-based force and torque limitations, this study proposes Variable Outer Radius Individually Addressable Coil Stacks (VORIACS), a novel magnetic actuation system optimized for high force output generation to magnetic devices within its workspace. The VORIACS marks significant improvements and breakthroughs in magnetic actuation within decimeter-scale workspace. The VORIACS is comprised of 12 coils that are optimized for 2D magnetic field generation under maximized power consumption of up to 12 kW. We implement six two-channel motor controllers, powered by six separate power supplies. Each of the twelve coils in the system is operated on its own motor-controller channel. This arrangement allows the system to exceed the magnetic forces and torques possible for single-coil versions of the same geometry. This study elaborates on optimizing, manufacturing, integrating, and demonstrating this system. Comparative analysis reveals that while a suboptimal, single-coil version of this system generates 0.31 N force (710 mT/m magnetic gradient magnitude), the VORIACS produces 1.673 N force (3834 mT/m magnetic gradient magnitude) on the same magnetic object placed 5 cm away from the coils. Moreover, the strong penetration force generated by VORIACS enables needle penetration to a mock gel that has the rigidity of liver tissue. In addition, we demonstrate the advantage of stacked coils with variable radii for magnetic field manipulability while maintaining the optimized force delivery property of the system, which improves control and could facilitate multi-tool manipulation. By enabling a fivefold increase in magnetic pulling force compared to its single-coil counterpart, VORICAS raises the potential penetration capabilities of untethered magnetic robotics in surgical procedures.