Meissner Effect Research Articles

The Meissner effect in neutron stars

Abstract We present the first model aimed at understanding how the Meissner effect in a young neutron star affects its macroscopic magnetic field. In this model, field expulsion occurs on a dynamical timescale, and is realised through two processes that occur at the onset of superconductivity: fluid motions causing the dragging of field lines, followed by magnetic reconnection. Focussing on magnetic fields weaker than the superconducting critical field, we show that complete Meissner expulsion is but one of four possible generic scenarios for the magnetic-field geometry, and can never expel magnetic flux from the centre of the star. Reconnection causes the release of up to ∼5 × 1046 erg of energy at the onset of superconductivity, and is only possible for certain favourable early-phase dynamics and for pre-condensation fields 1012 G ≲ B ≲ 5 × 1014 G. Fields weaker or stronger than this are predicted to thread the whole star.

Thermal quench modeling of REBCO racetrack coils under either alternating current or short-circuit voltage

Abstract Racetrack coils in REBCO High-Temperature Superconductor (HTS) motors help to increase the power-over-weight ratio by raising the magnetic flux density and output power. Nevertheless, HTS motors face thermal quench due to self-heating effects when subjected to alternating or short-circuit onset DC voltage. Additionally, thermal events have been observed due to screening currents when motors operate at high frequencies. Therefore, for the safe operation of HTS motors, quench research is crucial. To accurately simulate and analyze quench events in different scenarios, it is imperative to employ fast and precise software to numerically model the electrothermal behavior in racetrack coils. Our contribution involves the development of a novel and efficient model implemented in C++ that takes screening currents into account. This model is designed to conduct coupled electromagnetic and electrothermal analyses, utilizing variational methods. Specifically, the model incorporates both Minimum Electro-Magnetic Entropy Production and the Finite Difference Method. In this article, we explore the phenomenon of temperature rise within a racetrack coil subjected to either alternating or DC voltages of magnitudes ranging from 0.1 V to 1000 V. The study encompasses conditions of adiabatic operation and heat exchange with liquid nitrogen (LN2). Among other results, we found that in moderate DC voltages like 10 V, non-uniformity in the AC loss causes highly localized quench at the central turns. Then, screening currents play a key role also for DC voltages. The developed model exhibits the potential to comprehensively and swiftly analyze the electromagnetic and electrothermal characteristics of real-world superconducting applications, including high-field rotating machines, such as motors for aviation.

Perfect Diamagnetism of Polyaniline.

Herein, we report the synthesis of Fe-doped polyaniline (D-PANI). The onset of the diamagnetism is observed to be at T < 24 K under a weak external magnetic field. D-PANI was air-stable and showed the Peierls transition, as its resistivity increased rapidly at low temperatures, thus behaving as an electromagnetic insulator. The synthesized material showed high sensitivity to magnetic fields, with its diamagnetic character changing under a relatively low magnetic field (> 4.3 Oe) at 4 K. However, its resistivity remained almost constant at high temperatures, and the 1/T plots of conductivity indicated the nearest neighbor electron hopping conduction. Polarons (radical cations) in D-PANI behaved as localized charge carriers, showing perfect diamagnetism at low temperatures. X-ray photoelectron spectroscopy and X-ray fluorescence revealed that after purification, D-PANI contained C, N, O, S, and Fe but showed no electron spin resonance signal owing to its diamagnetism. Although superconductors show perfect diamagnetism, the synthesized PANI did not exhibit zero resistance; the perfect diamagnetism herein differed from the Meissner-Ochsenfeld effect. The polaron-derived perfect diamagnetism in a conductive polymer is a new magnetic phenomenon.

A problem with the conservation law observed in macroscopic quantum phenomena is a consequence of violation of the correspondence principle

Jorge Hirsch drew attention to the contradiction of the Meissner effect with Faraday’s law and the law of angular momentum conservation. This article draws attention to the fact that the angular momentum can change without any force only due to quantization in both microscopic and macroscopic quantum phenomena. But if in the first case this change cannot exceed the Planck constant, then in the second case this change is macroscopic due to a violation of the correspondence principle. To explain the violation of the correspondence principle, Lev Landau postulated in 1941 that microscopic particles in superfluid helium and superconductor cannot move separately. Quantization can change not only the angular momentum, but also the kinetic energy of a superconducting condensate on a macroscopic amount. For this reason, the Meissner effect and other macroscopic quantum phenomena contradict the second law of thermodynamics. The reluctance of physicists to admit the violation of the second law of thermodynamics provoked a false understanding of the phenomenon of superconductivity and obvious contradictions in books on superconductivity.

Solar technology for the production of Bi/Pb superconducting ceramics and its properties

Based on the experience of isostoichiometric and isostructural oxides production using solar energy, the prospects for synthesizing of Bi/Pb superconducting ceramics are shown. The principle of technology in the Large Solar Furnace (Parkent), the influence of gradient conditions on the formation of the oriented structure of crystallites-nuclei, and the connection of the innate properties of precursors with the lamellar morphology and phase composition of massive ceramics are described. The homophase composition of Bi/Pb ceramics was determined. Graphs of resistance and voltage of BSCCO in the temperature range 80-320K are presented. Anomalous of resistance and magnetic susceptibility in bismuth cuprates synthesized by solar energy were observed. Experimental graphs in resistance and magnetic susceptibility changes represent dependencies characteristic of the potential superconducting transitions. The manifestation of the Meissner effect at room temperature and normal atmospheric pressure and daylight, and under the influence of light is shown. The properties of Bi/Pb ceramics are explained by the connection with the innate properties of precursors obtained by concentrated solar energy.

A novel and fast electromagnetic and electrothermal software for quench analysis of high field magnets

Abstract High-field superconducting REBCO magnets contain several coils with many turns. For these magnets, electro-thermal quench is an issue that magnet designers need to take into account. Thus, there is a need for a fast and accurate software to numerically model the overall performance of full-scale magnets. High temperature superconductors can be modeled using different techniques for electro-magnetic and thermal (finite element method) analysis. However, it takes a lot of time to model the electro-magnetic and electro-thermal behavior of superconductors simultaneously, especially for non-insulated or metal-insulated coils. In addition, most of the available methods ignore screening currents, which are an important feature of REBCO magnets. We have developed a novel software programmed in C++, which performs coupled electro-magnetic and electro-thermal analysis using variational methods based on minimum electro-magnetic entropy production and finite difference, respectively. The developed software, which takes screening currents into account, is applied to axi-symmetric full scale magnets of more than 32 T field strength under the SuperEMFL project for thermal quench reliability during standard operation. We show that magnets incorporating non-insulated coils are more reliable against quench than metal insulated coils. Also, realistic cooling conditions at the boundaries are essential for such simulations. The model developed can be used for a quick and complete electro-magnetic and electro-thermal analysis of superconducting high field magnets.

A numerical approach to levitated superconductors and its application to a superconducting cylinder in a quadrupole field

Abstract Magnetically levitated superconductors in the Meissner state can be utilized as micro-mechanical oscillators with large mass, high quality factors and long coherence times. In previous works analytical solutions for the magnetic field distribution around a superconducting sphere in a quadrupole field have been found and used to derive the trap parameters, while non-spherical geometries have only been investigated in a few idealized cases. However, superconductors of almost arbitrary shape can be used as levitators in a magnetic trap and, as the trap’s properties depend strongly on the superconductor’s shape, allow for a wider parameter regime to be accessed. Finite element models are suitable to obtain the field distribution around arbitrarily shaped superconductors in arbitrary fields, but have not yet been used widely in the context of levitated superconductors. Here we present a simple numerical model for this purpose and use it to calculate the field distribution around cylindrical superconductors in a quadrupole field and to evaluate the trap parameters. We find that the cylindrical shape, compared to spherical levitators, allows for substantially higher trap frequencies and coupling strengths. This in turn reduces the demands on vibration isolation and significantly eases the requirements for feedback cooling to the ground state. The numerical model is provided in a file repository and can easily be adapted to various geometries and trap fields.

Reduced decay in Josephson coupling across ferromagnetic junctions with spin–orbit coupling layers

The generation of Sz = 1 triplet Cooper pairs has been predicted theoretically in superconducting–ferromagnetic hybrid heterostructures in the presence of spin–orbit coupling [F. S. Bergeret and I. V. Tokatly, Phys. Rev. B 89, 134517 (2014) and Jacobsen et al., Sci. Rep. 6, 23926 (2016)]. In this study, we experimentally investigate vertical Josephson junctions where the weak link is formed from a ferromagnetic layer with perpendicular magnetic anisotropy sandwiched by two non-magnetic layers with weak or strong spin–orbit coupling. We find that the decay of the Josephson coupling is reduced in the latter case, possibly indicating the presence of Sz = 1 spin-triplet correlations. We speculate that the canted magnetization required for these correlations is provided by the interaction of magnetization with Meissner effect in the superconducting layers.

Odd-frequency superfluidity from a particle-number-conserving perspective

We investigate odd-in-time—or —pairing of fermions in equilibrium systems within the particle-number-conserving framework of Penrose, Onsager, and Yang, where superfluid order is defined by macroscopic eigenvalues of reduced density matrices. We show that odd-frequency pair correlations are synonymous with even fermion-exchange symmetry in a time-dependent correlation function that generalises the two-body reduced density matrix. Macroscopic even-under-fermion-exchange pairing is found to emerge from conventional Penrose-Onsager-Yang condensation in two-body or higher-order reduced density matrices through the symmetry-mixing properties of the Hamiltonian. We identify and characterize a matrix responsible for producing macroscopic even fermion-exchange correlations that coexist with a conventional Cooper-pair condensate, while a matrix is shown to be responsible for creating macroscopic even fermion-exchange correlations from hidden orders such as a multiparticle condensate. The transformer scenario is illustrated using the spin-balanced s-wave superfluid with Zeeman splitting as an example. The generator scenario is demonstrated by the composite-boson condensate arising for itinerant electrons coupled to magnetic excitations. Structural analysis of the transformer and generator matrices is shown to provide general conditions for odd-frequency pairing order to arise in a given system. Our formalism facilitates a fully general derivation of the Meissner effect for odd-frequency superconductors that holds also beyond the regime of validity for mean-field theory. Published by the American Physical Society 2024

Investigation of Gamma-Induced Changes to Screening Currents and AC Losses in Mono- Versus Multi-filamentary REBCO Coated Conductors Using DC and AC Magnetometry

REBCO (rare-earth barium copper oxide) coated conductor tapes are a highly attractive option for magnet materials in future tokamak fusion power plants. However, the threat of intense neutron and gamma radiation, together with AC losses during magnet coil ramping, has raised concerns around magnet coil lifetimes. Irradiation-induced changes to flux creep rate has been identified as a key performance-limiting factor in REBCO tapes at low temperatures and high fields post-irradiation with gamma rays; spontaneous flux creep contributes to hysteretic AC loss in REBCO cables under applied AC fields. Knowing that multi-filamentary tapes are under consideration for tokamaks as an AC loss mitigation, magnetic measurements and gamma irradiation experiments are presented here on striated and mono-filamentary YBCO tapes to investigate the differences in post-irradiation screening currents and AC losses. Reduction in AC losses improved magnetisation critical current density (Jc) retention after 1 MGy in the multi- relative to the mono-filamentary samples. After the 5 MGy dose, striations then made the multi-filamentary tape more susceptible to Jc degradation because of the thinner individual filament width. Scanning transmission electron microscopy analysis on an analogous GdYBCO mono-filamentary tape did not indicate the introduction of nm-scale amorphisation to the active GdYBCO layer after gamma irradiation. A potential theoretical explanation for the underlying mechanism altering the flux-pinning landscape across the REBCO layer surface in gamma-irradiated tapes is discussed. This work concluded that gamma effects on screening current capability should be considered in future tokamak REBCO tape qualification studies.

Screening and Coupling Currents Induced Fields on a Large-Scale Prototype REBCO Insulated Coil

Screening and Coupling Currents Induced Fields on a Large-Scale Prototype REBCO Insulated Coil

Blowing in the dark matter wind

Interactions between dark matter and ordinary matter will transfer momentum, and therefore give rise to a force on ordinary matter due to the dark matter ‘wind.’ We show that this force can be maximal in a realistic model of dark matter, meaning that an order-1 fraction of the dark matter momentum incident on a target of ordinary matter is reflected. The model consists of light (mϕ ≲ eV) scalar dark matter with an effective interaction ϕ2ψ¯ψ\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$ {\\phi}^2\\overline{\\psi}\\psi $$\\end{document}, where ψ is an electron or nucleon field. If the coupling is repulsive and sufficiently strong, the field ϕ is excluded from ordinary matter, analogous to the Meissner effect for photons in a superconductor. We show that there is a large region of parameter space that is compatible with existing constraints, where the force is large enough to be detected by existing force probes, such as satellite tests of the equivalence principle and torsion balance experiments. However, shielding of the dark matter by ordinary matter prevents existing experiments from being sensitive to the dark matter force. We show that precise measurements of spacecraft trajectories proposed to test long distance modifications of gravity are sensitive to this force for a wide range of parameters.

Screening current in ultra-high-field non-insulated superconducting magnets

Screening current in ultra-high-field non-insulated superconducting magnets

Structural and superconducting properties in hard Mo2BC

The utilization of high-hardness superconducting materials enhances and broadens the applications of superconductors. In this study, a high-hardness Mo2BC superconductor is synthesized using the high-pressure and high-temperature (HPHT) method. Our results demonstrate that it exhibits zero-resistance and Meissner effect below a superconducting critical temperature (Tc) of 7.0 K. The upper critical magnetic field of 4.3 T and the lower critical magnetic field of 226 Oe were obtained by data fitting, respectively. Type-II superconducting properties were confirmed by critical states analysis and Ginzburg-Landau (GL) parameters. Specific thermal properties revealed a Debye temperature as 565.1 K, while an electron-phonon coupling (EPC) parameter λ of 0.588 indicated properly coupled BCS conventional superconductivity. Mo2BC exhibits a Vickers hardness of up to 18.2 GPa, significantly surpassing that of traditional superconducting ceramics. It can be attributed to the robust covalent boron-zigzag-chains coupled with appropriate covalent [Mo6C] octahedrons within a non-centrosymmetric structure. The coexistence of both superconductivity and high hardness enables the versatility of Mo2BC, thereby laying the way for the development of high-hardness superconductors.

Modelling the mechanics of 32 T REBCO superconductor magnet using numerical simulation

High-temperature REBCO superconducting tapes are very promising for high-field magnets. With high magnetic field applications there are high electromechanical forces, and thus a concern for mechanical damage. Due to the presence of large screening currents and the composite structure of the tape, the mechanical design of these magnets is not straightforward. In addition, many contemporary designs use insulated winding. In this work, we develop a novel two-dimensional axi-symmetric finite element tool programmed in MATLAB that assumes the displacement field to be within a linear elastic range. The stack of pancakes and the large number of REBCO tape turns are approximated as an anisotropic bulk hollow cylinder. Our results agree with uni-axial stress experiments in the literature, validating the bulk approximation. Here, we study the following configuration. The current is first ramped up to below the critical current and we calculate the screening currents and the forces that they cause using the minimum electromagnetic entropy production method (MEMEP) model. This electromagnetic model can now take insulated magnets into account. As a case study, a 32 T REBCO superconductor magnet is simulated numerically. We perform a complete mechanical analysis of the magnet by including the axial and shear mechanical quantities for each pancake, unlike in previous work where only radial and circumferential quantities were focused on. The effect on mechanical quantities without the screening current is also calculated and compared. It is shown that including the screening current-induced field strongly affects the mechanical quantities, especially the shear stress. The latter may be a critical quantity for certain magnet configurations. Additionally, in order to overcome high stresses, a stiff overbanding of different materials is considered and numerically modelled, which significantly reduces the mechanical stresses. The finite element-based model developed is efficient in calculating the mechanical behaviour of any general superconductor magnet and its devices.

Experimental study on screening-current induced strain in REBCO insert coils: under critical current control and operation current cycles

The screening-current effect is an inhomogeneous distribution of current density inside the REBCO conductors. The additional strain induced by the screening current, known as screening-current induced strain (SCS), is considered to affect the structural integrity of REBCO windings, especially when operating high-field REBCO insert magnets. In this work, we wound and tested a series of 50-turn REBCO coils inside a 10 T LTS external to investigate the influencing mechanism of multiple electromagnetic factors on SCS. We varied the critical current in different coils by different heat treatment procedures. Each coil was tested individually, experiencing a external field cycle and multiple operation current cycles at constant external fields. The extreme scenario for each coil was being energized to 400 A while the external field was 10 T. We adapted the discrete-coupled model to estimate the hoop strain distribution, monitored the experimental results by multiple strain gauges at the outermost turn. Test coil with a lower critical current endured a lower maximum hoop strain. When we were energizing the test coils, hoop strain increased at the edge of REBCO tapes while remaining nearly constant in the middle region. Additionally, the maximum hoop strain at the outermost turn decreased after each excitation cycle. This work could be an experimental reference for optimizing the electromagnetic design and the excitation scheme during the development of high-field REBCO magnets.

Effect of local and global screening current on the current decay in closed-loop HTS coils

High-temperature superconducting (HTS) coils are generally operated in a closed-loop persistent current mode, which is crucial for ensuring long-term stability and minimizing heat generation in various applications. However, factors such as joint resistance, flux creep, and losses due to external fields can lead to accelerated decay of the coil’s current, making it challenging to achieve an effective persistent current mode. To gain insight into the current decay characteristics of HTS coils, we built a finite element method based model coupled with a lumped parameter electric circuit model. The model is initially verified against the experiment of an inductive magnetized HTS coil subject to a magnetic field perpendicular to the tape surface. The results indicate that the proposed model is highly effective in predicting the current decay behavior of this magnetized HTS coil and is able to provide high accuracy. With the help of this model, we have experimentally and numerically studied the behavior of a current-carrying closed-loop HTS coil subject to external alternating fields. The HTS coil is charged by a DC power supply and then shorted using a thermally-controlled persistent current switch. The current decay behavior of the HTS coil is examined under various scenarios. The simulation results show excellent agreement with experimental data, further validating the effectiveness and versatility of the modeling strategy. The influence of both local and global screening currents on the current decay performance of the closed-loop HTS coils has been investigated. For every case examined, rapid demagnetization occurred in the initial cycle of the applied alternating field. Furthermore, the current decay rate demonstrated a slight dependence on the frequency of the applied fields. Additionally, the resulting resistance has been thoroughly characterized. These insights contribute to the knowledge of the behavior and performance of closed-loop HTS coils, facilitating their practical application.

Ginzburg-Landau equation and Meissner states of multiply-connected superconductors

This paper concerns the Ginzburg-Landau equation and the Meissner equations on a bounded multiply-connected domain in R3. The novelty of these equations is that both of them contain an unknown potential and an unknown Neumann field as the Lagrange multipliers. The minimal and non-minimal solutions for each equation are obtained by variational methods, and the effect of the applied magnetic field on the Meissner states is examined. The Meissner A-system with potential is also examined and a solution is obtained by using the Mountain Pass Lemma of Ambrosetti and Rabinowitz. In our analysis the estimates of the natural boundary value problem of the Maxwell-Stokes system play an important role.

Magnetic suppression for a possible Fe-poor organic–inorganic hybrid superconductor Fe14Se16(tepa)0.8 (tepa = tetraethylenepentamine) with a superconducting transition at ∼42 K

Composition/structure-dependent superconductivity for FeSe-based superconductors attracted great attention not only due to their high superconducting transition temperatures (TC), but also for understanding the origin of iron-based superconductivity. Here, we report a new Fe-poor organic-inorganic hybrid material Fe14Se16(tepa)0.8 with a paramagnetic-diamagnetic transition at ∼42 K grown by a high-temperature organic-solution-phase method with soluble iron/selenium sources in a tepa solution, alternative to previous intercalation strategies. The Fe14Se16(tepa)0.8 phase is in a tetragonal layered hybrid structure with a nanoplate shape. Composition analyses reveal a Fe-poor characteristic of the hybrid in contrast to previous FeSe-intercalated superconductor, and selected area electron diffraction pattern is featured by Fe3Se4 superstructures with a √2 × √2 of Fe vacancy order. Ab initio density functional calculations show that minus Fe3Se4 ions are stable in the hybrid and ∼0.25e−/Fe0.75Se is obviously larger than the reported values of approximately 0.2e−/FeSe in other FeSe-intercalated superconductors. Typical hysteresis loops and temperature dependence of dc/ac susceptibilities of the Fe14Se16(tepa)0.8 measured below ∼42 K suggest a presence of the Meissner effect in this material. Effects of synthesis conditions on structures and magnetic properties of the hybrids show a magnetic evolution from a long-range ferrimagnetic (FIM) order of Fe14Se16(tepa) to a coexistence of FIM and superconducting (SC) orders of Fe14Se16(tepa)0.9 and an SC order of Fe14Se16(tepa)0.8. X-ray absorption spectrum (XAS) confirms the presence of ferric/ferrous irons. Mössbauer studies reveal that the high-TC superconductivity originates from a suppression of the FIM order through tuning the spin states of irons from high-spin Fe3+ (S = 5/2) and Fe2+ (S = 2) in the Fe14Se16(tepa) to low-spin Fe3+ (S = 1/2) and Fe2+ (S = 0) in the Fe14Se16(tepa)0.8. Although no zero resistance is detected even at a temperature of 2 K, the resistivity at 2 K decreases by more than 1600 times compared to that in a normal state calculated by a variable range hopping (VRH) model, suggesting that the high-TC superconductivity of Fe14Se16(tepa)0.8 is possible.

Electric and dilatonic fields of a charged massive particle at rest in the field of a charged dilaton black hole

We study linear-perturbation equations for the two-body system of a charged dilaton black hole, of which dilaton coupling constant is α\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\alpha $$\\end{document}, and a static particle with mass m, electric charge q, and dilatonic charge βm\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\beta m$$\\end{document}. We find that a consistent condition for the coupled equations corresponds to the equilibrium condition of the test particle. The expressions of classical fields are given in closed analytical formulas in the most interesting case with β=α\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\beta =\\alpha $$\\end{document}. We examine the electrical field around a charged dilaton black hole especially in the limit of the maximum electric charge and we find the electric Meissner effect which has been found for the Reissner–Nordström black hole in the Einstein–Maxwell system.