Low-temperature Superconductors Research Articles

Demonstration of Different Magnet Technology in Colliders

The large hadron collider in high-energy physics is a very frontier and the state-of-art facilities in high energy physics with high level technical content and requirement. It is mainly composed of a particle accelerator that accelerate the particles, the detector which observe the reaction and the product of collision and the application of the high temperature and low temperature superconductor. However, due to the operation cost is pretty expensive, it requires high technical support. In this paper, we looking at the integration of data analysis that was established online as the study of the accelerator, detector and the superconductors, The operating principles , conditions required and the academic content of these three parts are analyzed, and then corresponding suggestions are given, such as reducing the low temperature environmental cost required by superconductors, improving the accelerators and detectors, future prospects and the suggestions given for the future development of superconductor materials. These results shed light on guiding further exploration of magnetic designs for colliders.

Strain Measurement in Single Crystals by 4D-ED

A new method is presented to measure strain over a large area of a single crystal. The 4D-ED data are collected by recording a 2D diffraction pattern at each position in the 2D area of the TEM lamella scanned by the electron beam of STEM. Data processing is completed with a new computer program (available free of charge) that runs under the Windows operating system. Previously published similar methods are either commercial or need special hardware (electron holography) or are based on HRTEM, which involves limitations with respect to the size of the field of view. All these limitations are overcome by our approach. The presence of defects results in small local changes in orientation that change the subset of experimentally available diffraction spots in the individual patterns. Our method is based on a new principle, namely fitting a lattice to (a subset of) measured diffraction spots to improve the precision of the measurement. Although a spot to be measured may be missing in some of the patterns even the missing spot can be precisely measured by the lattice determined from the available spots. Application is exemplified by heavily boron-doped silicon with intended usage as a low-temperature superconductor in qubits.

Design, construction and performance testing of a 1.5 T cryogen-free low-temperature superconductor whole-body MRI magnet

This work describes the design, construction and testing of a 1.5 T cryogen-free low-temperature superconductor niobium–titanium whole-body magnet with a bore diameter of 850 mm that is suitable for clinical magnetic resonance imaging (MRI) applications. The magnet is actively shielded and passively shimmed to achieve confinement within a 0.5 mT stray magnetic field at 2.5/4 m radial/axial positions and 12.1 ppm field inhomogeneity over a 45 mm diameter of spherical volume. The magnet is conductively refrigerated using a two-stage Gifford–McMahon cryocooler and can be maintained at a steady temperature below 5.7 K during MRI scanning. The MRI scanner assembled with the designed cryogen-free magnet demonstrated stable performance and provided MRI images with good quality and high contrast.

Anomalous Second Magnetization Peak in 12442-Type RbCa2Fe4As4F2 Superconductors

The second magnetization peak (SMP) appears in most superconductors and is crucial for the understanding of vortex physics as well as the application. Although it is well known that the SMP is related to the type and quantity of disorder/defects, the mechanism has not been universally understood. We selected three stoichiometric superconducting RbCa2Fe4As4F2 single crystals with identical superconducting critical temperature T c ∼ 31 K and similar self-field critical current density J c, but with different amounts of disorder/defects, to study the SMP effect. It is found that only the sample S2 with moderate disorder/defects shows significant SMP effect. The evolution of the normalized pinning force density f p demonstrates that the dominant pinning mechanism changes from the weak pinning at low temperatures to strong pinning at high temperatures. The microstructure study for sample S2 reveals some expanded Ca2F2 layers and dislocation defects in RbFe2As2 layers. The normalized magnetic relaxation results indicate that the SMP is strongly associated with the elastic to plastic (E-P) vortex transition. As temperature increases, the SMP gradually evolves into a step-like shape and then becomes a sharp peak near the irreversibility field similar to what is usually observed in low-temperature superconductors. Our findings connect the low field SMP of high-temperature superconductors and the high field peak of low-temperature superconductors, revealing the possible universal origin related to the E-P phase transition.

Low-Temperature Superconductor rf-SQUIDs-Based Fully Integrated Reflective-Type Analog Phase Shifter for Quantum Applications

This article presents a low-temperature superconductor (LTS)-based microwave phase shifter. The device utilizes a superconducting hybrid coupler monolithically integrated with two tunable reflective loads. An array of radio frequency superconducting quantum interference devices (rf-SQUIDs) is used to achieve inductive tuning in reflective loads, resulting in a broadband true time delay phase shift. The rf-SQUIDs are current controlled using an on-chip dc bias circuitry. The proof-of-concept fabricated device provides excellent RF performance in the <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${X}$ </tex-math></inline-formula> - and Ku -band with a phase shift of 49° at 10 GHz and 67° at 15 GHz. The insertion loss is < 1.5 dB for the entire range from 8 to 18 GHz. The methods to further improve the obtained phase shift are discussed. The overall device has a chip footprint of 0.6 mm2 and is fabricated using MIT-Lincoln Lab (MIT-LL) SFQ5ee eight-layer Niobium (Nb)-based superconducting fabrication process.

Status and powering test results of HTS undulator coils at 77 K for compact FEL designs

The production of low emittance positron beams for future linear and circular lepton colliders, like CLIC or FCC-ee, requires high-field damping wigglers. Just as compact free-electron lasers (FELs) require high-field but as well short-period undulators to emit high energetic, coherent photons. Using high-temperature superconductors (HTS) in the form of coated ReBCO tape superconductors allows higher magnetic field amplitudes at 4 K and larger operating margins as compared to low-temperature superconductors, like Nb-Ti.This contribution discusses the development work on superconducting vertical racetrack (VR) undulator coils, wound from coated ReBCO tape superconductors. The presented VR coils were modularly designed with a period length of 13 mm. Powering tests in liquid nitrogen of multiple vertical racetrack coils were performed at CERN. The results from the measurements are presented for three VR coils and compared with electromagnetic simulations.

Superconductivity in Ca3H2 electride at moderate pressure

The hydrogen-based electride Ca3H2 exhibits low-temperature superconductivity with both 0D and 2D interstitial electrons under ambient pressure, while maintaining its 2D electride nature and displaying good superconductivity under moderate pressures.

입자가속기용 초전도 코일 개발을 위한 절연설계법 개발

High-temperature superconductor (HTS) can be applied to manufacture superconducting coils for particle accelerators. Since HTS has a larger heat capacity than low-temperature superconductor (LTS), HTS is suitable for developing particle accelerators with fast ramp-up rate. A superconducting coil using HTS can be miniaturized with a fast ramp-up rate, thereby obtaining economic benefits such as reduction in maintenance and repair costs. High electric field intensity may be induced at a superconducting coil such as a saddle coil for medical accelerators owing to its complex structure. It is known that the dielectric performance of electrode systems can be poor in the medium vacuum range. In this study, dielectric experiments for establishing empirical formula to design a reliable HTS coil against fast ramp-up rate in various vacuum conditions were performed. As a result, empirical formula to design an electrically stable HTS coil were deduced through dielectric experiments with various conditions considering pressure, electrode size, and gap between electrodes.

Structure, design, and test of 13 kA HTS current lead

The 13 kA High Temperature Superconducting Current Leads (HTSCL) were designed and manufactured by the Institute of plasma physics, Chinese Academy of Sciences (ASIPP). This lead differs from former HTS current leads, in that it features an integrated heat exchanger (HEX) structure, a HTS magnetic shield and protective sleeve, and a Low Temperature Superconducting (LTS) module with a through cold conduction channel. The HTS and LTS module is cooled by SHe. In November 2020, the 13 kA steady-state test, Loss Of Flow Accident (LOFA) test, joint resistance test, pulse current test, insulation voltage test and other low-temperature electrical test items of the leads were completed. The test results indicate that all parameters meet the design requirements.

Quench detection and early warning based on thermoelastic strain rate for HTS tapes thermally triggered by heat spots

The rapid detection and comprehensive monitoring of quench onset and evolution in high-temperature superconducting (HTS) materials remains immensely challenging because the normal zone propagation velocity in HTS materials is two or three orders of magnitude less than that in low-temperature superconductors. In this study, we experimentally and numerically explore quench events triggered by heat spots in yttrium barium copper oxide HTS tapes to characterize the quench onset and propagation. A multiplexed fiber Bragg grating sensor with multiple gratings was used to perform highly accurate strain measurements. Conventional voltage and temperature measurements were performed synchronously on the HTS tapes. A systematic comparison of these multifield signals during quench onset and development illustrated that the evolution of thermoelastic strain and strain-rate in HTS tapes captures the quench onset and propagation. A distinct feature was exhibited during the quenching of a pre-tensioned HTS tape: the thermoelastic strain initially relaxed but subsequently increased until the strain rate exhibited a significant slope change, which corresponded to the quench onset time. The thermoelastic strain in a nearly unconstrained HTS tape gradually increased until quenching occurred. A prominent characteristic for detecting quench onset in HTS materials have been revealed based on the change in the slope of the thermoelastic strain-rate or the second derivative of the strain remaining nearly constant. For a pre-tensioned HTS tape, the minimization of the thermoelastic strain or the strain-rate becoming zero may be a predictor that preceded the quench by ∼1–2 s, which can be, to a certain extent, regarded as an early warning. Another important and novel result was the experimental demonstration of global strain responses distant from the quench location in the pre-tensioned HTS tape, while the temperature and voltage detection are commonly localized methods. The mechanism behind these thermoelastic strain characteristics was further discussed and simulated from the induced Joule heating throughout the quench event. The measurements and numerical predictions suggested a new paradigm of quench detection based on the thermoelastic strain-rate in HTS materials.

Mechanical strain triggering flux jumps of multi-filamentary Nb3Sn wires

The composite multi-filamentary Nb 3 Sn wire with a high critical current density is a preferred option for fabricating the superconducting magnet beyond the limit of NbTi wire (9-16 T). However, one crucial issue stems from the fact that electromagnetic force in superconducting coils is very strong, and the critical physical properties of Nb 3 Sn, such as J c , are more sensitive to mechanical strain than those of other possible low-temperature superconductors. We theoretically investigated the impact of mechanical strain on the thermomagnetic instabilities such as the flux jump (FJ) and quenching of Nb 3 Sn wire exposed to a static magnetic field and transport current. The good agreements with H formulation or H-φ formulation implemented on COMSOL software confirm the validity of our numerical simulations using home-made codes. It is discovered that mechanical strain can trigger flux jumps even in a static magnetic field. Furthermore, the threshold value of mechanical strain to trigger the first flux jump is a monotonic function of the static magnetic field in the case of high transport current, while it is a non-monotonic function in the case of low transport currents. It is attributed to the fact that flux can be released by the mechanical strain first, causing smooth flux penetration before triggering the flux jump. We also present the stable/unstable regions by applying mechanical strain by varying transport current, magnetic field, and working temperature, which helps in avoiding thermomagnetic instabilities while designing the superconducting magnet.

AC Loss Characteristics of HTS Novel Twisted Cables Composed of Soldered-Stacked-Square (3S) Wires

Compared with traditional cables, superconducting multi-stage cables have the natural advantages of greater transmission power and less energy loss, which have gradually attracted attention. However, conventional multi-stage cables are based on low temperature superconducting (LTS) technology and there is considerable scope for improvement in their performance. In this paper, a novel structure of the multi-stage high temperature superconducting (HTS) twisted cable prepared by the soldered-stacked-square (3S) wire is proposed. The AC loss characteristics of the twisted cable are deeply studied by experiments and simulation. Through the experiment, the influence of the voltage-leads on the AC loss measurement accuracy is eliminated, and frequency dependent is shown in the AC loss of the twisted cable. Besides, the simulated value of AC loss is consistent with the experimental value, which verifies the accuracy of the simulation. The AC loss of twisted cable is only 20% of that of the thin strip model, which reveals its outstanding advantages in AC loss.

Detecting Quench in HTS Magnets With LTS Wires—A Theoretical and Numerical Analysis

Protecting a high temperature superconducting (HTS) magnet from a quench event is a challenging task. Because of the slow normal zone propagation velocity, the long reliable quench detection method by directly monitoring coil voltage may not be timely for HTS anymore, leaving HTS magnets under danger of overheating. Using a NbTi low temperature superconducting (LTS) wire to detect quench in coils wound with ReBCO HTS tapes have recently been experimentally proved, yet a theoretical study is still needed to further develop this technique and make it prepared to be applied more generally in high field magnets. In this manuscript, we have demonstrated that it is the significant difference in the temperature dependence of critical current between LTS and HTS but not the normal zone propagation velocity (NZPV), that makes LTSs good quench detectors. Simulations show that LTS quench detectors should have low matrix fraction or high matrix resistivity. At last, at field up to 15 T or 20 T, Nb3Sn is proven to be a good quench detector.

Design and Optimization of the Superconducting Quadrupole Magnet Q1a in CEPC Interaction Region

To study the properties of Higgs, scientists from the Institute of High Energy Physics have proposed to build the Circular Electron Positron Collider (CEPC) and published a conceptual design report in 2018. In order to improve the collision luminosity of CEPC, the upgrade of the final focus system in the interaction region is on-going. According to the latest physical requirements of superconducting magnets in the CEPC interaction region, a high gradient, double-aperture quadrupole magnet Q1a is required, which is 1.9 m from the interaction point. In this paper, we present the magnetic design of superconducting quadrupole magnet Q1a, and discuss the advantages and disadvantages of the three kinds of quadrupole coil structures, including cos2θ coil, CCT coil, and racetrack coil. Low-temperature superconductor NbTi is used in our magnet design process. In addition, optimization is performed to greatly reduce the weight of the magnet.

Over-the-Gap Conductance Oscillations in Superconducting Vanadium Nanocontacts Induced by Hydrogen Impurities.

We have investigated the current-voltage (I-V) characteristics of Josephson junctions made by a low-temperature superconductor of vanadium (V) with a small amount of hydrogen (H) and deuterium (D) impurities using a mechanically controllable break junction (MCBJ) technique. Below the superconducting transition temperature TC, the differential conductance dI/dV spectra show distinct peaks within the superconducting gap, known as the subgap structure, which result from multiple Andreev reflections in pure V nanocontacts. Additionally, the H and D impurities in V nanocontacts induce several new conductance peaks outside the gap, referred to as an over-the-gap structures (OGSs). We found that the OGS peaks exhibit strong temperature dependence until the temperature is close to TC and follow the gap function predicted by BCS theory. When the contact diameter is changed at low temperature using the MCBJ technique, the OGS anomalies change almost linearly with the inverse of the contact diameter. In addition, the gap anomalies are significantly shifted outward by changing the positions of the H atoms through application of a high bias voltage between the contacts. The above features suggest that the OGS peaks are caused by the superconducting quasiparticle interference induced by H or D impurities and/or inhomogeneous structures in the nanocontacts.

Hidden magnetic order on a kagome lattice for KV3Sb5

${\mathrm{KV}}_{3}{\mathrm{Sb}}_{5}$ has recently attracted considerable attention due to its low-temperature superconducting properties, which are heralded by a charge-density wave. The apparent presence of a very weak magnetism does not result in long-range ordering. An explanation of the properties we present invokes higher-order terms in the vanadium magnetization density and a ``hidden order'' of Dirac (polar) multipoles. The Dirac dipole, known as an anapole or toroidal dipole, is one of a family of electronic multipoles visible in x-ray and magnetic neutron diffractions while undetectable with standard laboratory-based techniques. Actually, two viable magnetic structures, direct descendants of the established chemical structure, are studied with a view to testing their suitability in future experiments. One model structure is magnetoelectric and restricted to the linear type, whereas a second model cannot show a magnetoelectric effect of any type. The latter hosts a strange vanadium entity that is a true scalar and magnetic (time-odd), and associated in our paper with a fictitious charge distribution that is purely imaginary. Calculated x-ray and neutron-scattering amplitudes are symmetry-informed expressions of vanadium Dirac multipoles. Bragg diffraction patterns for the two models are found to be distinctly different, fortunately. Likewise, magnetochiral signals derived from our x-ray scattering amplitudes.

Observation of quantum criticality in antiferromagnetic based (Ce1Y )2Ir3Ge5 Kondo-Lattice system

• The chemical substitution dependencies of the three power law parameters have very similar behavior. • The minimum n exponent, maximum A coefficient, and ρo residual resistivity are at the same critical concentration x cr , expecting the sign for QCP in a non-Fermi Liquid (nFL) region. • Above x cr , the A values drop abruptly and the n values increase only slightly, indicating a transition from strongly to weakly correlated regime near the critical concentration x cr . We have carried out a detailed study of the (Ce 1 −x Y x ) 2 Ir 3 Ge 5 anti-ferromagnetic compounds across the entire range of substitution 0 ≤ x ≤ 0.33 and report the results of powder X-ray diffraction, magnetic susceptibility, heat capacity, and electrical resistivity measurements to exhibit the anti-ferromagnetic phase temperature ( T N ) versus substitution x phase diagram. The pure Ce 2 Ir 3 Ge 5 system indicates anti-ferromagnetic behavior below T N = 9.5 K. Substitution of Y into (Ce 1 −x Y x ) 2 Ir 3 Ge 5 compound leads to a decrease in the anti-ferromagnetic phase temperature ( T N ). Near x = 0.3, the anti-ferromagnetic transition temperature is suppressed to zero kelvin at an apparent anti-ferromagnetic quantum critical point, without the superconductivity sign, where the temperature dependence of the heat capacity and electrical resistivity in this region reveal non-Fermi Liquid behavior. The above results, for example, the suppressing of T N, maybe a new way to find low-temperature superconductivity in these compounds.

Effect of cubic and hexagonal boron nitride additions on the microstructure and properties of bulk MgB2 superconductors

MgB2 is a promising material for intermediate temperature applications where conventional low temperature superconductors cannot be used, especially if the range of magnetic fields over which is has acceptable current carrying performance can be expanded. However, its applicability is limited by poor properties at elevated magnetic fields. Carbon-based dopants can be used to dramatically improve the high-field performance of MgB2, but at the cost of a reduction in the superconducting transition temperature (T c) that limits the operation temperature to 20 K or below. Here we report an enhancement of superconducting performance of MgB2 with the addition of cubic and hexagonal boron nitride (BN), without any significant reduction in T c. Ex-situ bulk samples of MgB2 with two forms of BN addition were manufactured by the field assisted sintering technique after high energy ball milling of powder mixtures. We find that hexagonal BN (hBN) nanoparticles mixed homogenously with MgB2 powder react much more easily to produce Mg–N–B impurities than larger cubic BN (cBN) particles (∼10 µm) under the same processing conditions. The addition of 1 wt% hBN or 5 wt% cBN combined with 6 h of milling has been demonstrated to improve the critical current density (J c) of MgB2 over the entire magnetic field range. It is proposed that the nano-sized Mg–N–B impurities, that typically reside at MgB2 grain boundaries, increase pinning strength by introducing additional flux pinning centres. In addition, excess Mg may benefit the low-field performance by improving the connectivity. This work shows the significance of microstructural characterization on inhomogeneous superconducting materials to analyse their performance.

AbstAb-initio insights into the elastic, bonding, phonon, optoelectronic and thermophysical properties of SnTaS2

SnTaS2 is a layered topological semimetal exhibiting type-II low transition temperature superconductivity. Except some charge transport, electronic and superconductivity related properties, a number of the physical properties including elastic, mechanical, bonding, phonon dispersion, acoustic, thermal, and optical properties of SnTaS2 have not been explored comprehensively till now. In this work we have investigated all these physical properties of SnTaS2 employing the density functional theory (DFT) based first-principles methodology. It has been found that SnTaS2 is a mechanically stable, elastically anisotropic compound exhibiting strongly layered features. The bond hardness and Vickers hardness have been calculated. The material under study is ductile, soft and highly machinable. The chemical bonding has mixed character with significant contribution coming from the ionic channel. Phonon dispersion curves testify dynamical stability. Electronic band structure calculations show simple metallic character in agreement with previous results. The Fermi surface consists of both electron-like and hole-like sheets with varying degrees of energy dispersion. The low energy (encompassing the visible part of the optical spectrum) refractive index of SnTaS2 is high. The reflectivity is fairly nonselective over a wide range of photon energy and the absorption coefficient is large in the mid ultraviolet region. The Debye temperature and thermal conductivity of SnTaS2 are found to be low. The electron-phonon coupling constant has been calculated. SnTaS2 possesses optical anisotropy with respect to the polarization direction of the incident electric field.

Subscale HTS Fusion Conductor Fabrication and Testing in High Magnetic Background Field

In actual or future fusion machines like ITER, JT-60SA, W7-X or the present EU-DEMO design, low temperature superconductor (LTS) cables are used or planned to be used in the magnet system to create the strong magnetic field necessary for plasma confinement. High temperature superconductors (HTS) offer the potential to increase the magnetic field strength in fusion magnet systems even further, allowing to build more compact fusion machines or to realize higher flux swings in central solenoids. In this work, two HTS conductors were fabricated and characterized by high current testing at 77 K in self-field conditions and at 4.2 K with an external magnetic field up to 12 T. Both samples offer the same amount of superconducting HTS tapes but differ in the assembly process and termination type. These tests were intended to validate the current KIT design of a HTS CroCo triplet conductor and to qualify a low degradation cable manufacturing process.