Application Of High Magnetic Field Research Articles

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.

Development of high superconductor fraction (Ba, K)Fe2As2 wires with improved uniformity by two-axial rolling

Iron-based superconductors are regarded as prospective candidates for high magnetic field applications since they have very high upper critical field and low anisotropy. For practical applications, it is important to develop superconducting wires with strong current carrying capability. In this work, Cu/Ag composite sheathed (Ba, K)Fe2As2 (Ba-122) iron-based superconducting wires were fabricated by a two-axial rolling deformation process and a subsequent hot isostatic pressing (HIP) heat treatment. Compared with the previously reported Cu/Ag/Ba-122 wires prepared by groove rolling, the two-axial rolling allowed to use much thinner Cu/Ag composite sheath for wire fabrication, thus greatly increasing the filling factor of superconducting materials by about 5 times to 24 %, and lowering the volume fraction of silver down to 16 % in wires. By a comparative study on the microstructure and superconducting properties between the wires made by two-axial rolling and groove rolling processes, it is found that besides the significantly increased engineering critical current density, the former also exhibits improved homogeneity of mass distribution and uniformity of Ba-122/Ag interfaces, resulting in significantly enhanced n-values over 40 in magnetic fields up to 14 T. Our work suggests that two-axial rolling, combined with HIP processes, presents a promising approach to prepare iron-based superconducting wires with high filling factor, high uniformity and low cost for practical applications.

Fabrication of high-entropy alloy superconducting wires by powder-in-tube method

High-entropy alloys (HEAs) are novel functional materials that exhibit excellent mechanical and chemical properties. Recent discovery of self-healing superconductivity of HEAs under ion irradiation suggests their great potential applications under extreme conditions such as in nuclear fusion reactors or space environments. Here, we report a fabrication of the HEA superconducting (SC) wires using the ex-situ powder-in-tube (PIT) technique for the first time, a crucial stepping stone to achieve various industrial and technological applications. The Ta1/6Nb2/6Hf1/6Zr1/6Ti1/6 HEA SC powder prepared by planetary ball milling was filled into Fe tubes, drawn into wires, and then sintered in evacuated quartz tubes at various temperatures. The HEA SC wire sintered at 700 °C for 1 h exhibits the highest critical current density (Jc) among the HEA SC wires sintered in the temperature range of 600 – 1000 °C. At 4.2 K, the Jc of this wire exceeds the common benchmark value of Jc = 100 kA cm−2, indicating the suitability of the HEA wire for large-scale applications, such as in high-field SC magnets. The SC transition temperature (Tc) of the HEA wire significantly increases from 5.10 K for the as-cast wire to 7.58 K with the sintering time (ts) of 30 min at 700 °C. The scaling of the flux pinning force as a function of the magnetic field indicates that normal point pinning plays a major role in achieving a high in-field Jc in HEA SC wires. These results underscore the significant potential of HEA superconductors for practical applications in high-field SC magnets, SC electric machines, and next-generation nuclear fusion reactors.

Performance study of REBCO multi-filament tapes/CORC cables prepared by reel-to-reel mechanical incision

REBCO high-temperature superconductor (HTS) has widely used in high magnetic field applications, because of the excellent critical current properties and high critical temperature. However, REBCO tape has an extremely large width-to-thickness ratio (typically in the range of 1000–10000) to cause too high power dissipation in the applications. In order to reduce the shielding current effect and AC loss generated during the application of REBCO HTS tapes, a roll-to-roll mechanical incision device was developed for the preparation of REBCO multi-filaments tapes. The microscopic morphology, critical current IC, and hysteresis loss of the tapes before and after incision were comparatively characterized using optical microscope, standard four-probe method, and physical property measurement system (PPMS) and other equipment and methods. The results show that the developed device prepares multi-filaments tapes with incision grooves depths of ∼ 30 μm and grooves widths of ∼ 20 μm on the superconducting layer, and the hysteresis loss of the 3-filaments is reduced by up to 48.6 % compared to that of the non-striated tapes under different temperature conditions. In addition, the IC of the short samples of the 3-filaments tapes was reduced by ∼ 18 % compared with that of the non-striated tapes under 77 K and self-field test conditions, whereas the samples of the 3-filaments tapes and the non-striated tapes were hand-wound respectively onto a metal core with a diameter of 5.25 mm to make a single-layer CORC cable, and there was no significant reduction in the IC of either of them.

A 6-around-1 cable using high-temperature superconducting STAR ® wires for magnet applications

To generate a dipole field above 20 T, we need high-temperature superconductors, including REBa2Cu3O 7−x (RE = rare earth, rebco) coated conductors. However, the optimal architecture of a high-current flexible rebco cable is not yet settled for high-field magnet applications. Here we report a 6-around-1 cable concept based on the high-temperature superconducting star ® wires. We made two cable samples. One had a single star ® wire and the other had six star ® wires. The cable with six star ® wires was 1.5 m long. It had a diameter of 5.7 mm and a pitch length of 52 mm. The critical current of the cable before bending was 1448 A at 77 K, retaining at least 77% of the total critical current from individual star ® wires. The cable had a low n value around 4.5. At a bend radius of 30 mm, the critical current and n value remained the same as before bending. The total resistance of electrical terminations was 61 nΩ at 77 K. The flexible and transposed 6-around-1 star ® cable can provide another route toward practical rebco conductors for high-field accelerator and fusion magnet applications.

Effects of Different Magnetic Field Strengths and Duration on Seed Germination and Bacterial Growth

A magnetic field (MF) is an unavoidable environmental component for all organism. MF is constantly interacting with living systems and is known to influence a wide range of biological activities. Effects on organism are related to the strength and direction of the Earth's magnetic (geomagnetic) field variation. We aimed to investigate the effects of different magnetic field strength and also duration on seed germination (wheat and tomato) and bacteria growth (Bacillus and Staphylococus). The study was carried out in the presence of the magnetic resonance (MR) device. As a result of the measurements made in the MRI room, the organisms were subjected to a magnetic field of 0.2 and 1 Tesla. The seeds were exposed to the magnetic field for 4 days and the effects of each day were evaluated separately. The effect of the magnetic field varied interestingly with respect to the strength and especially by exposure time. The bacteria were exposed to two different magnetic fields continuously for 4 days. At the end of the application, morphological changes and zone diameters were determined. Seeds responded according to their genus and the magnetic field strength they were exposed to. Tomatoes were the most affected seeds in high magnetic field application, while wheat seeds were the least affected group. In bacterial growth, high tesla application increased the growth and pigment production of pigment bacteria, it was significantly reduced the growth of Staphylococcus bacteria. The findings have the unexpected implications that the germination can be effected associated with strength and exposure method. The effects and results of the magnetic field differ according to the species of organism used and even the variety and cultivars. A single paragraph of about 250 words maximum. For research articles, abstracts should give a pertinent overview of the work.

Enhancement of irreversibility field and critical current density of rare earth containing V0.60Ti0.40 alloy superconductor by cold-working and annealing

β-V1−xTix alloy superconductors are considered to be promising materials for high magnetic field applications. So far, attempts to improve the critical current density (JC) of β-V1−xTix alloys have shown limited success. Improving JC requires a controlled generation of defects. Similar to the V0.6Ti0.4-RE (RE = Gd, Y) alloys, RE = Ce, Dy and Nd are also immiscible in the V0.6Ti0.4 matrix. The superconducting transition temperature (TC), upper critical field (HC2), irreversibility field (HIrr), and JC increase with the RE addition. However, the tensile strength of V0.6Ti0.4-Gd alloy is observed to be significantly lower than that of V0.6Ti0.4 alloy. Cold-working is found to further improve the TC, HC2, HIrr, and JC of all the V0.6Ti0.4-RE alloys. Successive cold-working (with 50% reduction of thickness each time) and annealing (SCA) at 450∘C for 5 hrs is found to significantly improve the HIrr, and JC of V0.6Ti0.4-RE (RE = Gd, Ce) alloys. The tensile strength is also found to increase to about 60–70% of the V0.6Ti0.4 alloy after the third annealing. It is observed that α′ and ω phases form at the defect sites at various stages of cold-working and annealing. JC(H = 0) and HIrr are about 840 Amm−2 and 7 T respectively for the as-cast V0.6Ti0.4-RE alloys. Cold-working on the V0.6Ti0.4-RE alloys further improves the JC(H = 0) and HIrr to about 1250 Amm−2 and 8.45 T respectively. SCA increases the JC(H = 0) and HIrr to about 4000 Amm−2 (or more) and 9 T respectively, and the JC(7 T) to about 500 Amm−2 in V0.6Ti0.4-RE alloy at 4 K. We present a detailed description of the defect structure in these alloys and its role in pinning the magnetic flux lines, thereby improving the overall JC.

Conceptual design of hybrid IBS-REBCO magnet and a study on joint technology for high-field application

The REBa2Cu3Ox (REBCO) tape, known for its exceptional mechanical properties, stands as an optimal conductor for high-field applications. Nevertheless, stress degradation attributed to the membrane and monofilament structure of REBCO tape often occurs in high-field REBCO coils. On the other hand, iron-based superconductor (IBS) tapes offer notable advantages, including multifilament structure and upper critical field above 150 T, rendering it an appealing choice for high magnetic field applications. In this context, we first propose a methodology for designing a new type of compact hybrid magnet that integrates REBCO coils with multifilament IBS coils and a water-cooled resistive magnet to generate a high magnetic field. This paper presents the preliminary design of a hybrid magnet and employs a numerical simulation model to assess the magnet's electromagnetic and mechanical configuration, the simulation results show that the stress and strain experienced by all coils is within safe limits. Furthermore, details of the fabrication and testing of the IBS-REBCO joint are also provided. We hoped that the resistance of the IBS-REBCO joint would be less than 50 nΩ, however the resistance of the joint we developed did not meet our expectations. We discuss the reasons and propose the next plan to improve the performance of the IBS-REBCO joint.

Screening current induced field and its relaxation characteristics of CICC consisting of quasi-isotropic strands

With its high critical current density and excellent mechanical properties, second generation high temperature superconducting tapes (2G HTS) are attractive as high current conductors in power transmission and high magnetic field applications. Due to the high width to thickness ratio of the conductor, the screening current and screening current induced field (SCIF) caused by the alternating magnetic field during stacking cannot be ignored, and the instability of the central magnetic field due to the relaxation of the SCIF is also one of the problems studied in this paper. Therefore, the study of SCIF is important for superconducting magnets and power transmission applications. In this paper, the SCIF in quasi-isotropic stranded Cable-in-conduit conductor (QIS-CICC) is investigated by simulation. The effect of the amplitude and direction of the alternating magnetic field on the SCIF, is obtained by applying the alternating magnetic field to the different directions of the QIS-CICC. The simulation results are also compared with Twisted Stacked tape cable based CICC (TSTC-CICC), which are necessary for the design of the next generation of superconducting magnets.

Watch-sized 12 Tesla all-high-temperature-superconducting magnet

We demonstrate the construction of 7 Tesla and 12 Tesla all high-temperature-superconducting (HTS) magnets, small enough to fit on your wrist. The size of the magnet reduces the cost of fabrication, decreases the fringe field to permit facile siting of magnets, and decreases the stored energy of high field magnets. These small HTS-based magnets are being developed for gyrotron microwave sources for use in high-field nuclear magnetic resonance applications. The 7 Tesla and 12 Tesla magnets employ a no-insulation winding technique and are cooled to 4.2 Kelvin in a liquid helium cryostat. The 7 Tesla magnet is a single pancake coil, made of only 9.4 m of HTS tape, with an inner diameter of 8 mm and an outer diameter of 24 mm. This magnet was charged up to 1168 Amperes, generating a field of 7.3 Tesla. The 12 Tesla magnet is comprised of two pancake coils (inner diameter of 10 mm and outer diameter of 27 mm) connected in series. This magnet reached its maximum field at a current of 850 Amperes.

Metastable structures with composition fluctuation in cuprate superconducting films grown by transient liquid-phase assisted ultra-fast heteroepitaxy

Rare earth-barium-copper oxides superconducting tapes are key candidate materials for high-field magnet applications. The synergetic realization of high-speed growth and high field current carrying capacity of superconducting film is gaining prominence in academics and industry. In this paper, a pulsed laser deposition technique with an ultra-high growth rate two orders of magnitude higher than that of conventional methods (up to 100 nm/s) is engaged to grow nanocomposite EuBa2Cu3O7-δ (EuBCO) superconducting films. Dynamic heating and rapid quenching deposition process make intermediate phases to persist in the EuBCO matrix. As an evidence of the vapor-liquid-solid growth mechanism, a dome-like wetting structure composed of Ba–Cu–O and Eu-rich particles, is observed on the top of the EuBCO layer. In addition, high-density column-like copper-rich metastable amorphous structures appear from the EuBCO matrix to the dome-like structure, resulting in a high level of nanostrain and a large number of nano-defects (i.e., oxygen vacancies). The mixture of artificial and natural defects attributes to a pinning behavior dominated by random pinning at which the pinning force exceeds 345 GN/m3 at low temperature (20 K) and high field (14 T).

Vortex Dynamics and Pinning in CaKFe4As4 Single Crystals from DC Magnetization Relaxation and AC Susceptibility

Among various “families” of iron-based superconductors, the quite recently discovered AeAFe4As4 (where Ae is an alkali-earth metal and A is an alkali metal) has high critical current density, a very high upper critical field, and a low anisotropy, and has recently received much interest for the possibility of high magnetic field applications at the liquid hydrogen temperature. We have performed DC magnetization relaxation and frequency-dependent AC susceptibility measurements on high-quality single crystals of CaKFe4As4 with the aim of determining the pinning potential U*. The temperature dependence of U* displays a clear crossover between elastic creep and plastic creep. At temperatures around 27–28 K, U* has a very high value, up to 1200 K, resulting in an infinitesimally small probability of thermally activated flux jumps. From the dependence of the normalized pinning potential on irreversible magnetization, we have determined the creep exponents in the two creep regimes, which are in complete agreement with theoretical models. The estimation of the pinning potential from multifrequency AC susceptibility measurements was possible only near the critical temperature due to equipment limitations, and the resulting value is very close to the one that resulted from the magnetization relaxation data. Magnetic hysteresis loops revealed a second magnetization peak and very high values of the critical current density.

THE APPLICATION OF ANALYSIS OF VARIANCE TO DIFFERENT IRON‑BASED SUPERCONDUCTOR CRITICAL TEMPERATURE MODELING

Recently, Iron-based superconductors have shown promising properties of high critical temperature and high upper critical fields, which are prerequisites for applications in highfield magnets. Extensive research has been conducted on a modeling approach that contributes to predicting doped Iron-based superconductor critical temperature from structural and topological parameters. Statistical significance of differences in modeling approaches requires studies that can reliably distinguish between systematic approach effects and errors resulting from modeling approach variation. In this work, we introduce analysis of variance (ANOVA) to assess the statistical significance of differences in modeling approach variation. Comparisons of obtained results with Iron-based modeling approach variation data of support vector machine (SVM) and linear regression with natural logarithm transformation (LRNLT) were presented.

A practical stress-based test method for evaluating reversible stress limit for critical current degradation in rare-earth barium copper oxide (REBCO) tapes.

The superior electromechanical properties of second-generation high-temperature superconducting rare-earth barium copper oxide (REBCO) coated conductor tapes make them viable candidates for high magnetic field applications. To characterize their electromechanical properties (EMPs) under operating conditions, the critical current degradation behavior of the REBCO tapes should be evaluated. Conventional evaluation methods for EMPs usually rely on a strain-based test method that utilizes an extensometer to measure the deformation induced on the coated conductor tape. This study aims to establish a practical stress-based test method that determines the reversible stress limit for critical current (Ic) degradation in REBCO tapes without using extensometers under uniaxial tension. For an efficient test procedure, Ic measurements were initially performed with broad stress intervals and then changed to narrow stress intervals before the critical current degraded irreversibly. Four commercially available REBCO tape samples were used to validate the reliability of the proposed stress-based test method. It was then assessed by comparing them with those obtained using the conventional strain-based test method. Statistical estimations were used to determine the reproducibility of the results. These results provide a basis for an international round-robin test guideline to establish a test method for measuring the electromechanical properties of high-temperature superconducting tapes at cryogenic temperatures.

Effects of the oxygen source configuration on the superconducting properties of internally-oxidized internal-Sn Nb3Sn wires

We successfully manufactured 12-filament rod-in-tube Nb3Sn wires with oxide nanoparticles formed by the internal oxidation method. We employed Nb-7.5 wt%Ta-1 wt%Zr and Nb-7.5 wt%Ta-2 wt% Hf alloys along with oxygen sources (OSs) in two different configurations—in the core of Nb filaments (coreOS) and at the boundary between the filaments and the Cu tube (annularOS)—to assess the influence of the OS layout on the superconducting properties and grain size. The simultaneous presence of the OS and of Hf or Zr reduced the average Nb3Sn grain size to around 50 nm, leading to an enhancement of the layer critical current density (Jc ) up to 3000 A mm−2 at 4.2 K and 16 T for the Hf-annularOS wire. Samples manufactured with an OS show a shift toward higher reduced magnetic fields of the position of the maximum in pinning-force density, this shift being more pronounced when SnO2 is added in the annularOS configuration, and for the Hf-containing samples. This enhanced pinning at higher magnetic field is beneficial for high-field magnet applications. Moreover, we measured a very high upper critical field, reaching 29.3 T at 4.2 K in the Hf-annularOS samples.

Stress and Deformation Analysis of REBCO Pancake Coils With Individual Turn Movement

In recent years, rare-earth barium copper oxide (REBCO) pancake coils have shown excellent performances in high magnetic field applications. The no-insulation (NI) winding technique enables to enhance the thermal stability and current density of REBCO pancake coils. Still, further developments of REBCO coils are expected; e.g., the mechanical deteriorations of REBCO tapes caused by electromagnetic forces have been reported. The screening currents are considered as one of the causes to damage the REBCO tapes because of a nonuniform current distribution. Meanwhile, the electromagnetic forces on non-impregnant NI REBCO coils, whose windings can be deformed separately with turns and moved easily, are complicated, and the detailed mechanism has not yet been clarified. Commonly, the circumferential movement/deformation of the winding is considered as a rigid body. In this study, we investigate the stresses and displacements due to the electromagnetic forces on NI REBCO pancake coils in high magnetic field using a current simulation and a 2D elastic finite element analysis in the radial and circumferential directions; i.e., each turn can individually move in the radial and circumferential directions considering the spiral winding structure. The simulation results show the circumferential movement/deformation of windings and the nonuniform hoop stress due to the electromagnetic force.

Performance of low-loss demountable joints between CORC® cable-in-conduit-conductors at magnetic fields up to 8 T developed for fusion magnets

High-temperature superconductors (HTS) are promising candidates for use in the high-field magnets needed in particle accelerators and fusion reactors. HTS conductor on round core (CORC®) cables and wires wound from ReBa2Cu3O7-x (REBCO) coated tapes are being developed for use in high-field magnet applications including fusion magnets operating at currents beyond 80 kA, requiring them to be bundled into cable-in-conduit conductor (CICC) configurations. The use of HTS cables enable demountable superconducting fusion magnets that would allow easier access to the fusion machine for maintenance and parts replacement. Such demountable magnets require practical, low-resistance joints, capable of injecting current uniformly into the many REBCO tapes that make up different cable designs. Optimization steps on CORC® cables have resulted in high-current terminations and joints with a joint resistance measured between a pair of 30-tape CORC® cables of 51 nΩ at 76 K and 1.9 nΩ at 4 K. Demountable joints between CICCs consisting of six CORC® cables arranged in flat and round configurations were also tested and compared to joints between low-temperature superconducting (LTS) CICCs consisting of NbTi Rutherford cables. Samples were paired into two configurations (LTS-to-LTS and HTS-to-HTS) with a demountable joint between them that were each tested in series with currents up to 10 000 A in an applied background magnetic field of up to 8 T. The total loop resistance of the HTS-to-HTS sample, including their terminations and joint, was about 4 nΩ at 4 K in self-field with the resistance of the copper pressed joint being less than 1 nΩ. At 8 T, the total loop resistance increased to 6.9 nΩ with the pressed joint contributing 1.4 nΩ. These initial tests prove the feasibility of producing remountable (dry) joints with low resistance between superconducting magnet windings in future compact fusion machines.

Observation of Magnetic State Dependent Thermoelectricity in Superconducting Spin Valves.

Superconductor-ferromagnet tunnel junctions demonstrate giant thermoelectric effects that are being exploited to engineer ultrasensitive terahertz radiation detectors. Here, we experimentally observe the recently predicted complete magnetic control over thermoelectric effects in a superconducting spin valve, including the dependence of its sign on the magnetic state of the spin valve. The description of the experimental results is improved by the introduction of an interfacial domain wall in the spin filter layer interfacing the superconductor. Surprisingly, the application of high in-plane magnetic fields induces a double sign inversion of the thermoelectric effect, which exhibits large values even at applied fields twice the superconducting critical field.

Selective growth of metallic single-walled carbon nanotubes via the application of high magnetic fields of 10 T

The structure of carbon materials can be controlled using a magnetic field, enhancing their functional properties. Most of the magnetic-field effects on carbon material growth were found to originate from the magnetic-field orientation. However, we observed that the magnetic-field orientation did not affect the growth of single-walled carbon nanotubes (SWCNTs); instead, under a magnetic field of 10 T, the preferential growth of metallic SWCNTs (1-nm diameter) was observed using chemical vapor deposition and liquid decomposition, suggesting chirality selectivity. Raman and X-ray photoelectron spectra showed that the defect structure and oxygen content of SWCNTs increased with increasing magnetic-field intensity. Therefore, thin metallic nanotubes can be selectively grown by applying a high magnetic field in environments where nanotubes are relatively difficult to form.

Second magnetization peak, anomalous field penetration, and Josephson vortices in KCa_2Fe_4As_4F_2 bilayer pnictide superconductor

We performed magnetization measurements in a single crystal of the anisotropic bilayer pnictide superconductor KCa_2Fe_4As_4F_2, with T_c;simeq 34 K, for Hparallelc-axis and Hparallelab-planes. A second magnetization peak (SMP) was observed in the isothermal M(H) curves measured below 16 K for Hparallelab-planes. A peak in the temperature variation of the critical current density, J_{c}(T), at 16 K, strongly suggests the emergence of Josephson vortices at lower temperatures, which leads to the SMP in the sample. In addition, it is noticed that the appearance of Josephson vortices below 16 K renders easy magnetic flux penetration. A detailed vortex dynamics study suggests that the SMP can be explained in terms of elastic pinning to plastic pinning crossover. Furthermore, contrary to the common understanding, the temperature variation of the first peak field, H_1, below and above 16 K, behaves non-monotonically. A highly disordered vortex phase, governed by plastic pinning, has been observed between 17 and 23 K, within a field region around an extremely large first peak field. Pinning force scaling suggests that the point defects are the dominant source of pinning for Hparallelab-planes, whereas, for H parallelc-axis, point defects in addition to surface defects are at play. Such disorder contributes to the pinning due to the variation in charge carrier mean free path, delta l -pinning. Moreover, the large J_c observed in our study is consistent with the literature, which advocates this material for high magnetic field applications.