Transport Current Measurements Research Articles

Effect of transverse compressive stress applied at room temperature on Nb3Sn Rutherford cables

The accelerator magnets for the high luminosity upgrade of the large Hadron collider use Nb3Sn conductor to achieve the required in-field performance. To sustain the Lorentz forces during operation, a pre-compression is applied to the coils during the fabrication of the magnet. This can lead to an irreversible degradation of the Nb3Sn conductor due to its mechanical sensitivity. In this study, the impact of the pre-compression applied to the conductor at room temperature is investigated using a reacted double-stack specimen made of two Nb3Sn Rutherford cables. The cables have a keystone angle and are stack with a non-inverted configuration, without compensating the angle. The rectangular specimen is submitted to increasing transverse compressive stresses at room temperature applied perpendicularly to its width. The non-inverted configuration and the rectangular shape of the total specimen can thus lead to stress concentration. The pressure applied covers the range from 130 MPa to 190 MPa with a 10 MPa step increase. After each cumulated stress level, transport current measurements are performed in liquid helium and in background fields of up to 9.6 T in the FReSCa test station at CERN Metallographic analyses of several samples are made at selected stress levels. Monotonic and cumulated stresses are applied and the impact of mechanical cycling is analyzed. Procedures are specifically developed to minimize surface damage during samples’ preparation. The observations are compared with the electrical measurements in order to correlate the irreversible effect of the transverse pressure with the A15 damage state in the cross section. The transport current measurements of the double-stack specimen show degradation of critical current and n-value starting at respectively 170 MPa and 160 MPa cumulated loadings. However, cracks in the A15 phase are already observed in a metallographic sample subjected to 140 MPa.

Induced delamination in REBCO coated-conductor tape by a scratch line and bending

The aim of this work is to study delamination promotion of the coated conductor (CC) tape under the influences of the scratches on the Ag surface when bending. For this purpose, the microstructural and superconducting properties of the CC tape bent in helical fashion with different former diameters were analyzed. Such CC tape that exhibits visible damage along its length in the form of “scratch line” caused on the final product was used. The CC tape was bent at a constant lay angle of 45° with a superconducting layer positioned inward to the former core experiencing compression. Transport current measurements in liquid nitrogen were performed to study superconducting properties of the CC tape.The results showed that delamination of the REBCO (Rare-Earth Barium Copper Oxide) layer started to form exclusively on the scratch location at tube diameter of 7 mm (corresponding to strain ε = −0.71 %) while the rest of the REBCO surface started to delaminate at tube diameter of 5 mm (ε = −0.99 %). As the superconducting properties of the CC tape are related with the REBCO delamination, the critical current degraded when first signs of REBCO delamination appeared as expected. Thus, it was observed that the scratches induce REBCO delamination during the bending process resulting in increase of critical bending radius.

Transport Current Measurement of $I_{c}(T, B,\theta)$ and $n(T, B,\theta)$ for a Bulk REBCO Superconductor

Bulk rare-earth barium cuprate (REBCO) high-temperature superconductors are attractive for many electromagnetic applications due to their ability to support large current densities and trap large magnetic fields. At present, magnetisation techniques are the predominant method of measuring the critical current density, <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$J_\text {c}$</tex-math></inline-formula> , for bulk superconductors, due to the abundance of measurement devices and ease of sample preparation and measurement. However, this approach does not provide direct access to measurements of magneto-angular anisotropy of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$J_\text {c}$</tex-math></inline-formula> nor <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$n$</tex-math></inline-formula> -value. By contrast, transport current techniques allow direct measurement of the full thermo-magneto-angular dependence of both <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$I_\text {c}$</tex-math></inline-formula> and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$n$</tex-math></inline-formula> , but limited data is available for REBCO bulks, due to the difficulties of sample preparation and measurement. This work introduces a reproducible method to prepare a single-grain bulk GdBCO-Ag superconductor for transport current characterisation, and presents measured data for both <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$I_\text {c}$</tex-math></inline-formula> and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$n$</tex-math></inline-formula> that has been obtained over a broad parameter-space. The measured <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$n$</tex-math></inline-formula> -values are lower than is commonly assumed, with typical <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$n$</tex-math></inline-formula> -values at 77 K being in the range of 10 to 14. An accurate value of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$n$</tex-math></inline-formula> is required when computationally modelling transient effects.

Magnetic and Electromechanical Characterization of a High-JC RRP Wire for the HL-LHC MQXF Cable

In this work, we summarize the results of a series of inductive and transport measurements aimed at the evaluation of the electromechanical performance of a 0.85 mm diameter RRP wire procured for the HL-LHC project. The critical current dependence on the magnetic field and uniaxial applied strain (between −0.2 and 0.5%) has been investigated in a temperature range between 4.5 K and 10 K. Furthermore, the wire magnetization up to 12 T has been measured at different temperatures (4.3 K–14 K) to determine the wire's effective filament diameter and to complement the critical current density in the temperature and field range where transport current measurements were not available. The experimental results have been analysed in the framework of the Extrapolative Scaling Expression, by using a multi-step approach for the data fitting. These results provide an accurate parameterization of the critical surface in terms of field, temperature and strain, and can be used as a general reference for magnet design.

Single nucleobase identification for transversally-confined ssDNA using longitudinal ionic currents.

High-fidelity DNA sequencing using solid-state nanopores remains a big challenge, partly due to difficulties related to efficient molecular capture and subsequent control of the dwell time. To help address these issues, here we propose a sequencing platform consisting of stacked two-dimensional materials with tailored structures containing a funnel-shaped step defect and a nanopore drilled inside the nanochannel. Our all-atom molecular dynamics (MD) simulations showed that, assisted by the step defect, single-stranded DNA (ssDNA) can be transported to the nanopore in a deterministic way by pulsed transversal electric fields. Furthermore, different types of DNA bases can reside in the pore for a sufficiently long time which can be successfully differentiated by longitudinal ionic currents. By using the decoupled driving forces for ssDNA transport and ionic current measurements, this approach holds potential for high-fidelity DNA sequencing.

Experimental extraction of donor-driven spin relaxation in n -type nondegenerate germanium

Using pure spin current transport measurements in lateral spin-valve devices, we study the spin relaxation in an $n$-type nondegenerate Ge layer, which is moderately doped Ge (P: $\ensuremath{\sim}{10}^{18}$ ${\mathrm{cm}}^{\ensuremath{-}3}$). The obtained spin diffusion length $({\ensuremath{\lambda}}_{\mathrm{Ge}})$ of the nondegenerate Ge is two to three times greater than that of heavily doped degenerate Ge (P: $\ensuremath{\sim}{10}^{19}$ ${\mathrm{cm}}^{\ensuremath{-}3}$) in the temperature range from 8 to 100 K. We find that the electron spin lifetime ($\ensuremath{\tau}$) for the nondegenerate Ge is monotonically increased with decreasing temperature $(T)$. The increase in $\ensuremath{\tau}$ at temperatures less than 50 K can be interpreted in terms of the donor-driven spin relaxation mechanism including the 1/$\sqrt{T}$ behavior in multivalley semiconductors, proposed by Song et al. [Y. Song, O. Chalaev, and H. Dery, Phys. Rev. Lett. 113, 167201 (2014)]. We note that it is important for the $\ensuremath{\tau}$ of the moderately doped nondegenerate Ge to partly consider the $T$-independent component of spin relaxation in addition to the 1/$\sqrt{T}$ component.

Influence of transverse stress exerted at room temperature on the superconducting properties of Nb3Sn wires

Results on the irreversible degradation of Rutherford cables caused by transverse stress applied at room temperature have been recently published in the frame of the Future Circular Collider study for the 16 T dipole development programme. In order to investigate the degradation process of Nb3Sn composite superconductors, experiments based on wires of the same type as used in the cable have been launched. Nb3Sn wires produced by the Restacked-Rod Process were exposed to transverse stress at room temperature and the degradation of their properties was measured. Transport current measurements near the critical temperature at self-field and magnetisation measurements with a SQUID magnetometer were performed to determine changes in performance. In addition, metallographic preparations in combination with scanning electron microscopy were carried out to reveal cracks in sub-elements. In order to determine the stress distribution within the wire, especially the stress on the sub-elements, a finite element method analysis based on results from x-ray tomography was performed. The influence of transverse stress exerted at room temperature on the critical current density and intrinsic properties is analysed and compared with the microscopic observations.

Electromagnetic properties of REBaCuO superconducting tapes considered for magnets of fusion reactors

The RE-123 tapes represent the most advanced product in the field of high temperature superconductors, developed for transport of high electric currents. Although this product has already proceeded to the stage of industrial production, the variety in techniques employed by different manufacturers make the final products by far not identical. We studied electromagnetic properties of a series of 21 tapes from main global wire manufacturers. The tapes were tested by magnetic induction technique (vibrating sample magnetometer, VSM) and by a transport current measurements. The aim was to find the best candidates for superconducting coils for fusion reactors. Engineering currents were deduced from magnetic hysteresis loops measured by VSM at 10K, 50K, and 77K. The data for 77K were compared with the results of direct transport experiments done at the same temperature. Current transport experiments also provided information on the current anisotropy. The VSM tests were repeated after neutron irradiation of the tapes by neutron fluence of 2.12×1018cm−2. A significant enhancement of engineering currents was observed in magnetic fields above 0.5T in all investigated tapes and temperatures. The enhancement, similarly as the engineering current, was roughly exponential function of temperature.

Richardson-Schottky transport mechanism in ZnS nanoparticles

We report the synthesis and electrical transport mechanism in ZnS semiconductor nanoparticles. Temperature dependent direct current transport measurements on the compacts of ZnS have been performed to investigate the transport mechanism for temperature ranging from 300 K to 400 K. High frequency dielectric constant has been used to obtain the theoretical values of Richardson-Schottky and Poole-Frenkel barrier lowering coefficients. Experimental value of the barrier lowering coefficient has been calculated from conductance-voltage characteristics. The experimental value of barrier lowering coefficient βexp lies close to the theoretical value of Richardson-Schottky barrier lowering coefficient βth,RS showing Richardson-Schottky emission has been responsible for conduction in ZnS nanoparticles for the temperature range studied.

Evidence of superconductivity in doped graphite and graphene

We have observed evidence of superconductivity at temperatures in the vicinity of 260 K in phosphorus-doped graphite and graphene. This evidence includes transport current, magnetic susceptibility, Hall effect and (pancake) vortex state measurements. All of these measurements indicate a transition which is that of a type II superconductor with no type I phase until below the limits of our measurement capabilities. Vortex states are inferred from periodically repeated steps in the resistance versus temperature characteristics of highly oriented pyrolytic graphite and exfoliated doped multilayer graphene. Magnetic susceptibility measurements have shown results qualitatively similar to those expected (and experimentally observed by others) for ultra-thin (thickness ≪λL) films. The magnetization is negative for field-cooled and zero-field-cooled measurements. The magnetization for field cooled and zero-field-cooled measurements begin to diverge at approximately 260 K. Hall effect measurements show a sign reversal in the Hall voltage as the temperature is reduced from 300 K to 78 K.

Universality of non-equilibrium fluctuations in strongly correlated quantum liquids

Interacting quantum many-body systems constitute a fascinating playground for researchers since they form quantum liquids with correlated ground states and low-lying excitations, which exhibit universal behaviour. In fermionic systems, such quantum liquids are realized in helium-3 liquid, heavy fermion systems, neutron stars and cold gases. Their properties in the linear-response regime have been successfully described by the theory of Fermi liquids. However, non-equilibrium properties beyond this regime have still to be established and remain a key issue of many-body physics. Here, we show a precise experimental demonstration of Landau Fermi-liquid theory extended to the non-equilibrium regime in a 0-D system. Combining transport and ultra-sensitive current noise measurements, we have unambiguously identified the SU(2) and SU(4) symmetries of quantum liquid in a carbon nanotube tuned in the universal Kondo regime. We find that, while the electronic transport is well described by the free quasi-particle picture around equilibrium, a two-particle scattering process due to residual interaction shows up in the non-equilibrium regime. By using the extended Fermi-liquid theory, we obtain the interaction parameter "Wilson ratio" $R=1.9 \pm 0.1$ for SU(2) and $R=1.35 \pm 0.1$ for SU(4) as well as the corresponding effective charges, characterizing the quantum liquid behaviour. This result, in perfect agreement with theory, provides a strong quantitative experimental background for further developments of the many-body physics. Moreover, we discovered a new scaling law for the effective charge, signalling as-yet-unknown universality in the non-equilibrium regime. Our method to address quantum liquids through their non-equilibrium noise paves a new road to tackle the exotic nature of quantum liquids out-of-equilibrium in various physical systems.

&lt;inline-formula&gt; &lt;tex-math notation="TeX"&gt;$\hbox{BaHfO}_{3}$&lt;/tex-math&gt; &lt;/inline-formula&gt;-Doped Thick &lt;inline-formula&gt; &lt;tex-math notation="TeX"&gt;$\hbox{YBa}_{2}\hbox{Cu}_{3}\hbox{O}_{7-\delta} $&lt;/tex-math&gt; &lt;/inline-formula&gt; Films on Highly Alloyed Textured Ni-W Tapes

YBa 2 Cu 3 O 7-δ (YBCO) films with a thickness of up to 2 μm containing nano-sized BaHfO 3 (BHO) have been grown on biaxially textured metal tapes by pulsed laser deposition. Transmission electron microscopy revealed the inclusion of Y 2 O 3 platelets and rod-like BHO structures. A c-axis oriented growth of the YBCO layer and biaxial oriented incorporation of BHO is confirmed by X-Ray diffraction. BHO expands the c-axis of YBCO, flattens the surface of YBCO and densifies the films. Y 2 O 3 inclusions get smaller and finer distributed, possibly with a positive influence on pinning effects. A superconducting transition temperature T c of about 89 K was determined, decreasing slightly with increasing BHO content. Transport current measurements in the maximum Lorentz force configuration showed an increased irreversibility field H irr and higher pinning force density F p with increasing BHO content in high magnetic fields.

Accuracy of Florida Current Volume Transport Measurements at 27°N Using Multiple Observational Techniques

AbstractFor more than 30 years, the volume transport of the Florida Current at 27°N has been regularly estimated both via voltage measurements on a submarine cable and using ship-based measurements of horizontal velocity at nine historical stations across the Florida Straits. A comparison of three different observational systems is presented, including a detailed evaluation of observational accuracy and precision. The three systems examined are dropsonde (free-falling float), lowered acoustic Doppler current profiler (LADCP), and submarine cable. The accuracy of the Florida Current transport calculation from dropsonde sections, which can be determined from first principles with existing data, is shown to be 0.8 Sv (1 Sv ≡ 106 m3 s−1). Side-by-side comparisons between dropsonde and LADCP measurements are used to show that the LADCP-based transport estimates are accurate to within 1.3 Sv. Dropsonde data are often used to set the absolute mean cable transport estimate, so some care is required in establishing the absolute accuracy of the cable measurements. Used together, the dropsonde and LADCP sections can be used to evaluate the absolute accuracy and precision of the cable measurements. These comparisons suggest the daily cable observations are accurate to within 1.7 Sv, and analysis of the decorrelation time scales for the errors suggests that annual transport averages from the cable are accurate to within 0.3 Sv. The implications of these accuracy estimates for long-term observation of the Florida Current are discussed in the context of maintaining this key climate record.

Rectifying differences in transport, dynamic, and quasi-equilibrium measurements of critical current density

The dependence of the critical current density (Jc) on electric field criteria (Ecr) is studied for high-quality YBCO (YBa2Cu3O7) thin films over the entire applied magnetic field (Ba) range. The quantitative model describing the Jc(Ba) dependence is compared and explained for the critical current densities obtained by different measurement techniques. Transport current and quasi-equilibrium magnetization measurement data can successfully be fitted by the model with appropriate electric field criteria. The dependence of the irreversibility field on the Ecr criterion can be obtained within the model. At the same time, the dynamic magnetization measurements of the Jc(Ba) curves strongly depend on instrumentally defined parameters, introducing inconsistencies in the experimental results. Therefore, the model calculations are able to explain the Jc(Ba) curves only if the instrumental vibrations affecting vortex behaviour are taken into account. However, the nature of the observed dependence on the vibration of the samples is unclear. Different frequencies of the sample vibrations have been investigated. It is revealed that if the frequency tends to zero, the Jc(Ba) curves are well described by the model. We have outlined a number of possibilities which may be responsible for the behaviour observed. However, none of the existing theories can explain the effect of the vibrations, which exponentially degrade the irreversibility field to a certain tampered Birr value at frequencies larger than ≃25 Hz.

Critical current density: Measurements vs. reality

Different experimental techniques are employed to evaluate the critical current density (Jc), namely transport current measurements and two different magnetisation measurements forming quasi-equilibrium and dynamic critical states. Our technique-dependent results for superconducting YBa2Cu3O7 (YBCO) film and MgB2 bulk samples show an extremely high sensitivity of Jc and associated interpretations, such as irreversibility fields and Kramer plots, which lose meaning without a universal approach. We propose such approach for YBCO films based on their unique pinning features. This approach allows us to accurately recalculate the magnetic-field–dependent Jc obtained by any technique into the Jc behaviour, which would have been measured by any other method without performing the corresponding experiments. We also discovered low-frequency–dependent phenomena, governing flux dynamics, but contradicting the considered ones in the literature. The understanding of these phenomena, relevant to applications with moving superconductors, can clarify their dramatic impact on the electric-field criterion through flux diffusivity and corresponding measurements.

Field mapping measurements to determine spatial and field dependence of critical current density in YBCO tapes

In this paper a measurement method that allows the determination of the critical current density of superconducting tape from field mapping measurements is presented. This contact-free method allows obtaining characteristics of the superconductor as a function of the position and of the applied flux density. With some modifications, this technique can be used for reel-to-reel measurements. The determination of the critical current density is based on an inverse calculation. This involves calculating the current distribution in the tape from magnetic measurements. An YBaCuO tape has been characterized at 77K. A defect in this superconductor has been identified. Various tests were carried out to check the efficiency of the method. The inverse calculation was tested theoretically and experimentally. Comparison with a transport current measurement was also performed.

The phase boundary of superconducting niobium thin films with antidot arrays fabricated with microsphere photolithography

The experimental investigation of the Ic(B)–Tc(B) phase boundary of superconducting niobium films with large area quasihexagonal hole arrays is reported. The hole arrays were patterned with microsphere photolithography. We investigate the perforated niobium films by means of electrical directed current transport measurements close to the transition temperature Tc in perpendicularly applied magnetic fields. We find pronounced modulations of the critical current with applied magnetic field, which we interpret as a consequence of commensurable states between the Abrikosov vortex lattice and the quasihexagonal pinning array. Furthermore, we observe Little–Parks oscillations in the critical temperature versus magnetic field.

Metallurgical Processes in NbTi Filaments as a Function of Isothermal Annealing Time

Abstract In an attempt to improve understanding between pinning behaviour and underlying microstructures, results of the investigation on multifilamentary Cu/Nb-47w%Ti alloy are presented. Wire was drawn to final size without intermediate stage thermomechanical treatments. Cold worked structure was subjected to isothermal annealing at 648 K for various annealing times between 2 minutes to 100 hours. Microstructural and compositional features were studied by transmission electron microscopy, TEM, and analytical TEM equipped with EDS analyzer. The pinning behavior was monitored by the maximum volume pinning force determined using transport current measurements at 4.2 K up to 9 T. According to the present results, the average grain boundary spacing remained rather constant at 45 nm throughout all annealing times while the average grain boundary width increased from the initial dimension of 1 nm to 1.8 nm after 100 hours as a result of precipitation processes at grain boundaries. Further, distributions of the grain boundary widths changed from a sharp shape to a wider spectrum of widths. The precipitation process created titanium concentration gradients in the vicinity of the grain boundaries. As the annealing time increased, the sharp gradients became shallower and Ti concentrations as low as 35 w% Ti were observed after 40 hours. High field pinning at 9 T was associated with structures having a mean grain boundary width of 1.2 nm and titanium concentration gradients on a scale of 2.5 to 5 nm from the grain boundaries. Mid magnetic field pinning was favored by microstructures having titanium gradients on a scale of 5-10 nm and the mean width of 1.5 nm while improved low field pinning at 3 T was associated with microstructures having the mean width of 1.8 nm, shallow gradients and titanium concentrations as low as 35 w% inside of the grains.

Dual Activity of Aminoarylthiazoles on the Trafficking and Gating Defects of the Cystic Fibrosis Transmembrane Conductance Regulator Chloride Channel Caused by Cystic Fibrosis Mutations

A large fraction of mutations causing cystic fibrosis impair the function of the cystic fibrosis transmembrane conductance regulator (CFTR) chloride channel by causing reduced channel activity (gating defect) and/or impaired exit from the endoplasmic reticulum (trafficking defect). Such defects need to be treated with separate pharmacological compounds termed potentiators and correctors, respectively. Here, we report the characterization of aminoarylthiazoles (AATs) as compounds having dual activity. Cells expressing mutant CFTR were studied with functional assays (fluorescence-based halide transport and short circuit current measurements) to assess the effect of acute and chronic treatment with compounds. We found that AATs are effective on F508del, the most frequent cystic fibrosis mutation, which is associated with both a gating and a trafficking defect. AATs are also effective on mutations like G1349D and G551D, which cause only a gating defect. Evaluation of a panel of AAT analogs identified EN277I as the most effective compound. Incubation of cells expressing mutant CFTR with EN277I caused a strong stimulation of channel activity as demonstrated by single channel recordings. Compounds with dual activity such as AATs may be useful for the development of effective drugs for the treatment of cystic fibrosis.

Influence of Transport Current Distribution on AC Transport Current Loss Measurement in an Assembled Conductor

We investigated the validity of AC transport current loss measurement in a high temperature superconducting (HTS) assembled conductor using the four-terminal method. We tested the effect of different arrangements, transport current direction, and transport current distribution in the assembled conductor. Neither the arrangement nor direction of the transport current affects the accuracy of the AC transport current measurement. When transport current distribution in an assembled conductor is unbalanced, it is possible to deduce the loss by the addition of the multiple of the current and voltage from the potential lead loops in each tape. If the transport currents in each HTS tape of the assembled conductor are not uniform and only transport current of the assembled conductor is measured, the AC transport current loss is not estimated exactly.