Self-magnetic Field Research Articles

Efficient Calculation of the Self-Magnetic Field, Self-Force, and Self-Inductance for Electromagnetic Coils

Efficient Calculation of the Self-Magnetic Field, Self-Force, and Self-Inductance for Electromagnetic Coils

Electromagnetic and thermal performance study on a canted stack of REBCO tapes

Abstract Due to the critical current limitation of a single REBCO tape, stacking methods are generally employed to increase the current carrying capacity in practical high-temperature superconducting (HTS) applications. However, the overall critical current is strongly dependent on the self-magnetic field, which is influenced by the geometrical arrangement of conductors in the stack. Due to the brittle ceramic property, REBCO tapes are conventionally bent along the thickness side of the tape. However, the difference in bending radii of the outer and inner tape surfaces in the stack may lead to fracture deformation, thereby limiting the stacking number of REBCO tapes. To balance the stacking number with the bending issue, canted stack is proposed as a variant of normal stack for REBCO tapes. As a potential HTS intermediate component, it is imperative to conduct a comprehensive study on electromagnetic and thermal performance of canted stack. The unique geometrical arrangement of canted stack introduces new factors that affect critical current and transport AC loss. This paper concludes the special influencing factors of canted stack, including canted angle, stacking number, tape width, and spatial structure. The metal interleaving method is introduced for spatial distribution changing and thermal stability. Furthermore, orthogonal analysis is performed to elucidate the comprehensive correlation among these multiple factors. This study provides insights into the overall critical current and transport AC loss for different combinations of canted stack and establishes a predicting function for critical current to support the structural design of canted stack. Based on the specific case study, the improvement effect of canted stack is confirmed by both experiments and simulations.

Effect of Size of a Circular Tokamak Plasma on Self-Magnetic Field: A Numerical Approach

Effect of Size of a Circular Tokamak Plasma on Self-Magnetic Field: A Numerical Approach

Plasma characteristics and material erosion mechanism in multi-channel wire electrical discharge machining

Multi-channel wire electrical discharge machining (MC-WEDM) is an advanced and high-efficiency machining technology, but its material erosion mechanism remains unclear. In this study, dual-channel wire electrical discharge machining was utilized as a case study to investigate the impact of the plunging current on both the plasma characteristics and material erosion under complex discharge conditions. Force analysis was conducted on the charged particles in the plasma, revealing that the plunging current can influence the trajectory of the plasma by modifying the self-magnetic field. The particle tracking method was employed to simulate the motion of electrons, revealing that in MC-WEDM, electrons exhibited a larger and more uniform distribution. The evolution of the plasma within a single-pulse discharge was observed using high-speed photography technology, and the discharge signals collected from different channels were analyzed. It was observed that the plasma in MC-WEDM experienced more intense back-and-forth sweeping on the workpiece surface, facilitating the ejection of molten metal from the molten pool. The oscillating plasma exhibits a larger processing area and a more uniform distribution of energy, resulting in the formation of larger and shallower discharge craters. Furthermore, the influence of the amplitude and time point of the plunging current on the volume and area of the discharge craters was summarized. Finally, MC-WEDM significantly reduced the occurrence of holes and micro-cracks and exhibited a thinner recast layer in the continuous discharge experiment.

Numerical modelling of heating and melting of metal in a mini industrial direct current electrical arc furnace

Purpose The purpose of this paper is the study of the electro-vortex flow (EVF) as well as heating and melting processes for mini industrial direct current electric arc furnace (DC EAF). Design/methodology/approach A mini DC EAF was designed, manufactured and installed to study the industrial processes of heating and melting a small amount of melt, being 4.6 kg of steel in the case under study. Numerical modelling of metal melting was performed using the enthalpy and porosity approach at equal values and non-equal values of the solidus and liquidus temperatures of the metal. The EVF of the liquid phase of metal was computed using the large eddy simulation model of turbulence. Melt temperature measurements were made using an infrared camera and a probe with a thermocouple sensor. The melt speed was estimated by observing the movement of particles at the top surface of melt. Findings The thermal flux for metal heating and melting, which is supplied through an arc spot at the top surface of metal, is estimated using the thermal balance of the furnace at melting point. The melting time was estimated using numerical modelling of heating and melting of metal. The process started at room temperature and finished once whole volume of metal was molten. The evolution of the solid/melt phase boundary as well as evolution of EVF patterns of the melt was studied. Originality/value Numerical studies of heating and melting processes in metal were performed in the case of intensive liquid phase turbulent circulation due to the Lorentz force in the melt, which results from the interaction of electrical current with a self-magnetic field.

Improvement of Superconducting Joint Properties for GdBa2Cu3Ox Bulk Superconductors Joined with ErBa2Cu3Ox Superconductor Using Local Melt-Growth Method.

The important factors in obtaining a high-quality superconducting joint were investigated for the superconducting joint of a GdBa2Cu3Ox (GdBCO) bulk superconductor with sintered ErBa2Cu3Ox (ErBCO) using the local melt-growth method. REBCO (RE: rare earth) bulk superconductors can be used as strong magnets by magnetizing them, but they require large bulk sizes for their application. Although the superconducting joint presents a viable solution, many possibilities for property improvement remain, such as property degradation, depending on the joining direction. By varying the joining thermal conditions and confirming the elemental distribution, magnetization properties near the joined part and the effects of these on the joining properties are clarified, and a method for fabricating high-performance joined samples is obtained. Microstructure segregation was rarely observed at the center of the joined part regardless of the joining direction, and the superconducting properties were negligible and small. The Jc-B results are almost identical to those of the GdBCO matrix at a low field, confirming that the joined part minimally interferes with the superconducting current. Furthermore, by lowering the maximum temperature, shortening the holding time at the maximum temperature, and increasing the cooling rate, the region of mutual solid solution was reduced, and the Jc-B under the self-magnetic field was enhanced. These results contribute to the development of the superconducting joining method, a critical aspect of larger bulk superconductors.

Effect of Tensile Stress on Self-Magnetic Leakage Field in Carbon Steel Pipe Material

Metal magnetic memory (MMM) technique is a promising non-destructive technology for determining the state of material deformation and structural defect in carbon steel pipe by measuring the self-magnetic leakage field (SMLF). The relationship between SMLF and stress concentration of cracked specimens has been extensively researched, but little is known about corrosion defects in carbon steel pipes, such as circular holes. A static tensile test and MMM measurement were performed on the ASTM A106 Gr. B steel to investigate its applicability in predicting material deformation state and structural defect. The tensile load makes the distribution of self-magnetic leakage field, SMLF intensities in the elastic stage regular. In the defect zone of defective specimens, a peak-trough in the SMLF intensity in the tangential component, Hp(x), and a peak in the normal component, Hp(y), were observed. As yield approached, the SMLF intensities remained unchanged. During plastic deformation, dislocation slip and dislocation interaction rarely change the SMLF intensities and its gradient. The SMLF intensities and its gradient rise as the tensile load approach its ultimate strength. The distribution of SMLF intensities show a peak feature in the Hp(x), and a peak-trough in the Hp(y) as the specimen fractures. Variations in the magnetic and stress fields of carbon steel pipe are caused by structural defect. As a result, the SMLF intensity varies. The method described in this study can be applied to MMM technique to detect material deformation states and defect formation in ASTM A106 Gr. B steel at low cost and with minimal equipment.

Experimental Study on Evolution Law of Self-Magnetic Leakage Field during the Fatigue Process of Steel Weld

Experimental Study on Evolution Law of Self-Magnetic Leakage Field during the Fatigue Process of Steel Weld

A Stress Measurement Method for Steel Strands Based on Spatially Self-Magnetic Flux Leakage Field

Metal Magnetic Memory (MMM) exhibits the advantage of not requiring embedded sensors or external excitation, making it suitable for inspecting ferromagnetic components in engineering structures. This study introduced MMM into stress detection of steel strands. Graded tensile tests were conducted on the steel strands to investigate the correlation between Self-Magnetic Flux Leakage (SMFL) signals and stress levels. Different spatial detection positions with varying Lift-Off Values (LOV) and Rotation Angle Values (RAV) were set to examine the distribution of spatial SMFL field under load. Furthermore, a magnetic characteristic parameter AN was proposed to assess the stress level of the steel strands. The results indicate that the rate of change in the middle region of the SMFL curve was lower than that at the beginning and the end. Additionally, with increased applied load, the SMFL curve exhibited systematic variations, and the dispersion of the normal component curve gradually decreased. By utilizing the magnetic characteristic parameter AN, the stress in the steel strands can be calculated, with the parameters determined based on LOV and RAV. This achievement expanded the nondestructive testing methods for steel strands and holds significant research value.

Development of a Compact HTS-FAIR Conductor for Magnet Application

Research and development of large-current capacity high temperature superconducting (HTS) conductors for magnet applications in nuclear fusion experimental devices is underway in the world. As a candidate conductor, the FAIR conductor has been developed, in which REBCO tapes and pure aluminum sheets are alternately stacked in an aluminum jacket, and the lid is covered by friction stir welding (FSW) method. Producing several prototypes of FAIR conductors, current transport tests have been repeatedly conducted in liquid nitrogen without an external magnetic field to optimize the manufacturing process of the conductor. In addition, we have also investigated the properties of the conductors in low temperature under high magnetic fields. As the next step, we have been planning to conduct coil shape tests in high magnetic fields. For installation in a test facility, we have developed a reduced diameter FAIR conductor from 12 mm to 6 mm. 1.5 rotations/m reduced version of FAIR was fabricated and current transport tested in 77 K, self-magnetic field. Compared with the results of critical current analysis considering the self-magnetic field, the retention of <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">I</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</sub> was 67%. After cutting the fabricated the compact FAIR conductor and observing the inside, it was found that the REBCO tapes were folded by FSW. Therefore, it was found that further optimization of the FSW process was necessary.

Basic Research of Magnetic Field Distribution around the Superconducting Cable for DC Power Transmission Cable Application

We studied the self-magnetic field distribution around the BSCCO superconducting cable core at various condition of applied current. The magnetic field densities perpendicular to the tangent of the outer circumference of the cable was measured by rotating the Hall sensor around the cable. Firstly, we performed measurements with basic conditions such as energize tape one by one to confirm the accuracy of our system and the observed value was in good agreement with the calculation. Measurements were also performed with currents flowing in two tapes either with same or opposite directions, and it was also found that the magnetic field distribution when current is passed through two tapes at the same time is different from the sum of the magnetic field distributions when current is passed through each tape independently.

Quantitative linear correlation between self-magnetic flux leakage field variation and corrosion unevenness of corroded rebars

The accurate uneven cross-sectional area probability distribution of corroded rebars is critical to the reliability assessment of the corroded reinforced concrete structure. The cross-sectional area and self-magnetic flux leakage variation data of 22 naturally and 6 applied current corroded rebars were obtained via 3D light measurement and micromagnetic scanning technologies. The experimental correlation of the self-magnetic flux leakage field variation ratio dH(x/z) and the corrosion unevenness degree dSn of the corroded rebar was then analyzed and verified by finite element modeling. The experimental and simulated results indicated that dSn had a quantitative linear correlation with dH(x/z) with a ratio of about 1, which was proved to be functionally equivalent to the well-established rebar cross-sectional area spatial heterogeneity factor R in the structural reliability assessment. This quantitative linear correlation is not affected by the corrosion style, the magnetization differences, and the corrosion degrees of different rebars, based on which the structural reliability assessment could have higher accuracy and better adaptability for the mutative external aggressive environment.

Optimized superconducting MgB2 joint made by IMD technique

A novel type of superconducting joining technique has been introduced to join unreacted internal Mg diffusion (IMD) single-core MgB2 wires. Our method is based on fabricating a small diameter joint mould obtained by deforming an Nb/Cu composite tube with a longitudinal semi-cylindrical Mg and B core into a thick round wire. The small diameter of the joint provided advantages such as rapid cooling, low resistance, and the unique core design inside the joint ensured a uniform MgB2 phase formation. Scanning electron microscope analysis revealed that the IMD MgB2 wires had excellent contact with the superconducting MgB2 bulk material inside the joint. The joint resistance, calculated from the decay of the trapped magnetic field over time, is a quite low value of 6.44 × 10−16 Ω at 20 K. The transport critical current (I c) of the joint is 62 A at 20 K under a self-magnetic field, and the n-value of the joint is 66 at 20 K under 1.5 T. The results showed that the I c of our joint can be determined precisely, regardless of whether the magnetic field is applied from low to high or from high to low value during I–V measurements.

Ratchet Effect in Triangle-Shaped Vertical Nb/TiO/Nb Josephson Junctions

We fabricate vertical Nb/TiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</sub> /Nb Josephson junctions with the shape of right-angled isosceles triangles of different sizes. The TiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</sub> layer is primarily metallic, indicating that our junctions belong to the superconductor-normal metal-superconductor (S-N-S) junction. When applying bipolar dc currents across the junctions in parallel magnetic fields, there are many obvious differences between the positive and negative parts of the current-voltage characteristics. We attributed this asymmetry behavior (or ratchet behavior) mainly to the asymmetric pinnings for Josephson vortex penetration at the asymmetric edges (the right-angled corner and the hypotenuse) of the triangled junction, in addition to the effect of current-induced magnetic self-fields. For comparison with superconducting thin-film ratchets, the rectified dc voltages of our junctions with applied ac currents are investigated at different temperatures, magnetic fields, and driving frequencies. The waveforms of the time-resolved voltage with sinusoid currents are also measured. The ratchet effect in the junctions decreases monotonically with increasing temperature, increases to the peak first, and then decreases with the increasing magnetic field. It remains almost unchanged in the driving frequency range of 0.1 to 100 kHz. Compared with Abrikosov vortex ratchets, the ratchet effect in the junctions is much more sensitive to temperatures far from <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">T</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</sub> , demonstrating the larger temperature-regulating window. This article shows the distinct influence of the asymmetric junction boundaries on the characteristics of the junctions under certain conditions, which can be useful for further understanding and inspiring new applications of Josephson junctions.

Research on Typical Displacement Current Peak in Relativistic Magnetron Priming

During the operation of the relativistic magnetron (RM), the sudden change of voltage waveform will produce displacement currents that play a prominent role in assessing the operation state of magnetron, while they have been neglected in the previous research. Therefore, in this article, we introduce a novel method to analyze the working state of the magnetron in the starting stage by using the typical displacement current peak (TDP). The theoretical analysis shows that the TDP in a well-matched RM is attributed to the asynchrony between the mutation of self-magnetic field and electron beam, and the appearance of the TDP means the slow oscillation establishment or sluggish electron beam growth in the RM. According to such theory, we present a method to improve the operation state of RM and eliminate the TDP, and it is verified in our experiment. This work is beneficial for diagnosis and adjustment of RM working state in priming.

Finite Element Analysis of AC Losses in Pancake Coils Wound Using Two-Ply Bundle Conductor

AC losses in stacked bundle conductors exposed to external magnetic fields are numerically evaluated using a two-dimensional finite element method formulated with a self-magnetic field owing to currents induced in an analysis region. The bundle conductor is composed of two pieces of (Re)BCO coated conductors without electrical insulation to improve the thermal stability. In the analysis models, an idealized copper layer is sandwiched between a pair of superconducting layers in every bundle conductor. The external magnetic fields are increased monotonically from zero to simulate the electromagnetic responses in parts of a single pancake coil for a high field magnet. To understand only the geometrical effect on AC loss, the superconductors are assumed to be subject to the Bean model, in which the critical current density is independent of the local magnetic field. The influences of the number of bundle conductors, gap between bundle conductors, and applied angle of the magnetic field on AC loss are investigated.

Radial dependence of the self-magnetic field in a free-electron laser

Radial dependence of the self-magnetic field in a free-electron laser

Study of Deformation Behavior of AISI 1025 Carbon Steel with Different Microstructures Using Metal Magnetic Memory and Acoustic Emission Testing

Studies are carried out to investigate the tensile deformation behavior of AISI-type 1025 carbon steel with different microstructures using metal magnetic memory and acoustic emission testing (AE) techniques. Seven AISI 1025 carbon steel specimens were heat treated for different microstructures and then subjected to tensile deformation until fracture. AE was conducted during tensile deformation and the deformation-induced self-magnetic leakage fields (SMLFs) were measured using a giant magneto-resistive sensor after unloading. Results reveal that SMLF signal values are influenced by microstructure and residual stress aroused due to plastic deformation. Among different specimens, SMLF signal peak amplitude is highest in the brine-quenched specimen followed by the tempered specimen, while hardness is highest in the brine-quenched specimen. SMLF signal peak amplitude and hardness are the lowest in the annealed specimen. SMLF signal is higher in tempered specimens compared to the untempered specimens. From AE measurements, it is observed that martensitic steel emits higher acoustic emissions during deformation but decreases when tempered. The acoustic emissions generated in the martensitic steel are also of higher amplitude. The results are correlated with optical micrographs and hardness measurements.

Investigation of self-generated magnetic field and dynamics of a pulsed plasma flow

Due to the growing interest in studying the compression and disruption of the plasma filament in magnetic fusion devices and Z-pinches, this work may be important for new developments in the field of controlled thermonuclear fusion. Recently, on a coaxial plasma accelerator, we managed to obtain the relatively long-lived (∼300 μs) plasma filaments with its self-magnetic field. This was achieved after modification of the experimental setup by using high-capacitive and low-inductive energy storage capacitor banks, as well as electrical cables with low reactive impedance. Furthermore, we were able to avoid the reverse reflection of the plasma flux from the end of the plasma accelerator by installing a special plasma-absorbing target. Thus, these constructive changes of the experimental setup allowed us to investigate the physical properties of the plasma filament by using the comprehensive diagnostics including Rogowski coil, magnetic probes, and Faraday cup. As a result, such important plasma parameters as density of ions and temperature of electrons in plasma flux, time dependent plasma filament’s azimuthal magnetic field were measured in discharge gap and at a distance of 23.5 cm from the tip of the cathode. In addition, the current oscillograms and I–V characteristics of the plasma accelerator were obtained. In the experiments, we also observed the charge separation during the acceleration of plasma flow via oscillograms of electron and ion beam currents.

Experimental substantiation of diagnostic parameters used in metal magnetic memory method

Tensile testing of steel specimens under 'soft' and 'hard' loading conditions with simultaneous measurement of the self-magnetic field of the specimens using the metal magnetic memory (MMM) method is performed. By comparing the obtained tensile diagrams with magnetograms of the self-magnetic field variation, the relationship between the magnetic and mechanical characteristics at different stages of loading is determined. It is found that the self-magnetic field variation magnetograms of the specimens closely correspond to the true tensile diagrams. The ratios between the magnetic and mechanical characteristics, obtained during tensile testing of the specimens, allow for the determination of the limiting state of the metal at the time of crack formation using the measured magnetic parameters in stress concentration zones when performing practical diagnostics of equipment.