Particle irradiation offers a route to incorporating additional flux pinning centres in high-temperature superconducting wires with minimal disruption to the pre-existing defect landscape, thereby further enhancing the critical current in a controllable fashion. This work is a comprehensive study of the fluence-dependence of proton irradiation using protons of two energies, 2.5 and 1.2 MeV, in enhancing the critical current performance in commercially available (Y,Dy)Ba2Cu3O7-delta coated conductors. A sequence of fluences covering the range from 1 x 1015 to 5 x 1016 protons cm-2 was used in the irradiation process to study the flux pinning in this material. The resulting samples were characterized using field angle-dependent transport critical current measurements over a range of temperatures from 20 K to 77.5 K and magnetic fields up to 8 T, thus covering the wide range of operating conditions. Optimisation of fluence for highest performance at each energy resulted in a similar level of isotropic critical current enhancement, a factor 2.6 improvement at 20 K and 8 T, but with a significant difference in the optimised fluence in each case. The lower energy 1.2 MeV protons produce this enhancement at a three-fold lower fluence compared to 2.5 MeV protons, a result of their higher electronic energy loss. The different samples are analysed within the framework of the maximum entropy model, helping to understand the vortex dynamics before and after irradiation.

We have used silver-ion irradiation and proton irradiation to produce point-like and spherical defects in REBa 2 Cu 3 O 7 coated conductors. We compare the resulting pinning landscape for optimized fluences and show that proton irradiation gives a slightly greater pinning enhancement at 20 K, but in the same samples silver irradiation gives significantly better pinning enhancement at 65 K. We attribute this to the relative sizes of the defects and to the distribution of defects resulting from the different ion collision rates.

Particle irradiation using light ions and heavy ions is found to be an effective method to introduce flux-pinning centers into REBCO films and coated conductors. The degree of enhanced critical current at various conditions depends upon the size, morphology, and orientation of ion tracks. Proton irradiation to the optimised fluence results in greater isotropic enhancement at lower temperatures, the enhancement decreases as temperature increases. Silver ion irradiation on the other hand gives a greater enhancement at higher temperature but limited to particular angular ranges. We compare the results of these two types of irradiation and then produce a mixed pinning landscape with a combination of the two. We find a nearly isotropic enhancement in Ic at lower temperatures and an enhancement about the c -axis direction, similar but broader than silver irradiation alone, at higher temperatures.

Heavy-ion irradiation of solids produces damage tracks with radii typically of the order of 1 nm, depending on the ion species and energy. In cuprate superconductors this is close to the coherence length, which makes these defects highly effective flux pinning centers. Varying the ion-beam energy allows tuning of the dimensionality of the defects created, with higher-energy ions tending to produce columnar tracks and lower-energy ions tending to produce point-like defects. Starting with consistent production-standard REBCO tape from American Superconductor we have explored the energy-dependence of silver-ion irradiation and characterized the irradiated samples with angle-dependent transport critical current measurements. Using silver ions with energies in the range 50 MeV to 150 MeV and fluence of 4 × 1011 ions/cm2 we have been able to tune the irradiation-induced damage from point-like defects to columnar tracks, manifesting in changes to the pinning landscape ranging from isotropic critical current enhancement to the production of strong peaks in the angle dependence of critical current.

Normal-incidence irradiation by 100 MeV Ag ions is used to improve flux pinning in previously optimised commercial REBCO tapes from the American Superconductor Corporation. We observe distinct critical-current anisotropy enhancements below and above 40 K. Above 40 K a strong c -axis peak appears in the angular dependence of the critical current, as is usually expected upon the introduction of columnar defects. The critical current is enhanced significantly but only for a limited range of field angles. Close to the parallel-field direction there is no enhancement or even a reduction in critical current. Below 40 K, on the other hand, the enhancement is much broader with respect to field angle, creating an almost isotropic response at 20 K, 3 T. The absence of a prominent c -axis peak does not indicate a lack of pinning, since the absolute value of the critical current still increases by a factor of 2.8 compared to an unirradiated sample. Instead, we postulate that pre-existing point-like pinning centres act to mediate an interaction between the existing planar and newly-introduced columnar pins, broadening both contributions. The point-like pins become less effective with increasing temperature as the coherence length increases, leading to a reduction in this interaction and a separation of the individual peaks relating to planar and columnar pins. At 20 K, we achieve an enhancement in the angular-minimum critical current by a factor of 2.7, in a material that had already been process-optimised for low-temperature pinning.

Ion irradiation of REBCO films and coated conductors, in which the ions pass completely through the REBCO film, produces damage tracks which form near-ideal flux-pinning defects. The radius and aspect ratio of the tracks depends on the mass and energy of the incident ions. We have investigated the effect of Ag ion irradiation, at different incident energies and incidence angles, on REBCO production-quality coated conductors from American Superconductor Corp. Transmission electron microscopy and in-field transport critical current anisotropy analysis indicates that the ion-energy threshold for the formation of elongated tracks is around 50 MeV. At this energy tracks are not readily identifiable in low-resolution TEM, and enhancement of critical current is nearly isotropic. For a higher ion energy of 100 MeV, on the other hand, clear elongated (but still not fully continuous) tracks are visible in TEM, and the critical current is anisotropic with strong enhancement occurring when the applied field is parallel to the ion incidence angle. We particularly analyze the case of 60° inclined irradiation. This produces a clear peak in the field-angle dependence of critical current for 100 MeV irradiation, but only an incipient peak for 50 MeV irradiation. The incipient peak can be identified by curve fitting using a minimal number of maximum-entropy functional components.

The magnetic-field anisotropy of the critical current is an extrinsic property of superconducting wires that is of greatest relevance to the design of high temperature superconducting (HTS) devices. It is also a highly useful diagnostic tool to understand the dominant flux-pinning mechanisms active in different temperature and field regimes. REBa2Cu3O7 (REBCO) coated conductors typically exhibit a large peak in critical current when the field is aligned with the REBCO a-b plane. The commercial pinning-enhanced American Superconductor Corporation (AMSC) REBCO coil wire used for this study is unusual in having a relatively small a-b plane peak at higher temperatures due to an inherently low density of stacking faults. Stacking faults can then be introduced by annealing the wire in oxygen to create the more commonly observed strong a-b plane peak. Complementary c-axis columnar defects can be added by silver ion-irradiation producing an additional peak in the critical current at 0°. The resulting complex critical current anisotropy is studied using transport critical current measurements over a temperature range from 20 K to 77.5 K and under magnetic fields up to 7 T. Through systematic studies on pristine and annealed samples, in the presence and absence of columnar defects created by silver irradiation, we investigated the flux-pinning interactions between stacking faults and columnar defects.

The field-angle dependence of the critical current in a REBa2Cu3O7 coated conductor has been measured over a fine range of temperatures from 15 K to 80 K. The particular sample is demonstrated to have a very low fraction of extrinsic planar defects by its near-isotropic critical current at 77 K. At a representative magnetic field of 3 T we are able to track the emergence of the ab-plane peak usually associated with intrinsic pinning and quantify its evolution with temperature by fitting to a maximum-entropy function. We are also able to observe the evolution of dip and peak features in the angle dependence of the power-law index n with decreasing temperature and show that a dip appearing at 65 K is supplanted by a sharper positive peak from 50 K. The combination of critical current and power-law index temperature dependences shows the onset of intrinsic pinning at 50 K.

YBa2Cu3O7-based coated conductors (CCs) achieve the highest critical current densities (J(c)) of any known superconductor and are a key technology for applications such as rotatory machines, high-field magnets and power transmission. Incorporation of nano-sized non-superconducting second phases as additional vortex pinning centers has been considered the most amenable route to further enhance J(c) at an industrial scale, and has been successfully used in commercial CCs. The resulting pinning landscape is quite complex, with both synergistic and competing interactions among the various types of defects. Particle irradiation, on the other hand, allows for a controlled post-processing incorporation of a well-defined defect morphology. We have previously shown that irradiation with protons and other light ions can further enhance the in-field J(c) in commercial state-of-the-art CCs. Here we develop a combined irradiation process that increases J(c) above values previously achieved by irradiating with only one species. Our new approach involves sequentially irradiating with 250 MeV Au ions and 4 MeV protons. For example, at T similar to 27 K (liquid neon) and mu H-0 similar to 4 T, a region of interest for rotatory machines applications, we obtain J(c) similar to 5 MA cm(-2), which is about 40% higher than the values produced by the individual irradiations. Finally, we conclude that this is due to the synergistic pinning effects of the introduced splayed, non-uniform columnar defects and small clusters.

This article provides an update on the Rolling Assisted Biaxially Textured Substrate (RABiTS™) technology used for the preparation of flexible, long length, single crystal-like templates for the manufacture of the Second Generation (2G) high temperature superconducting wire. The RABiTS technology, originally developed in 1996, is based on the formation of a biaxially textured metal alloy foil upon which a series of epitaxial oxide films are deposited. The RABiTS technology is currently used by multiple companies to manufacture 2G wire that is being used in a number of commercial and military applications.

We use atomically resolved scanning transmission electron microscopy and electron energy loss spectroscopy to determine the atomic-scale structural, chemical and electronic properties of artificial engineered defects in irradiated-annealed high temperature superconducting wires based on epitaxial Y(Dy)BCO film. We directly probe the oxygen vacancy defects in both plane and chain sites after irradiation with 18-meV Au ions. The plane site vacancies are reoccupied during post-annealing treatment. Our results demonstrate the dynamic reversible behavior of oxygen point defects, which explains the depression and recovery of self-field critical current and critical temperature in irradiation-annealing process. These findings reveal the strong effect of oxygen vacancies in different sites on the superconductivity properties of irradiated Y(Dy)BCO film, and provide important insights into defects engineering of 2G HTS coil wires.

The microwave properties of polypyrrole, polyaniline and poly(3-hydroquinonylpyrrole) films were examined as a function of doping level, conductivity, counter anion and thickness. The microwave transmittance of the polymer films was varied from less than 10% to greater than 90% by oxidizing and reducing the polymers. The potential use of conductive polymers in the design of an electromagnetic modulator for the tunable attenuation of microwave radiation is described.

Raman microspectroscopy (RMS) and imaging Raman microscopy (IRM) were used to probe the composition and spatial distribution of chemical phases in Bi(Pb)–Sr–Ca–Cu–O (BSCCO) ceramic superconductor powders and silver-BSCCO composites. The Raman techniques were used to identify various phases, including alkaline earth cuprates, CuO, Bi-2212, Bi-2223, and Pb-containing phases. Changes in the Ca/Sr ratios in (Ca, Sr)2CuO3 phases were distinguished by differences in orientation with respect to polarization of the exciting radiation. Variations were observed in the content and distribution of lead in various phases formed during intermediate stages of the thermal processing of composite conductors. The spatial distribution of the various phases detected in powder and composite conductors was established to a resolution of a few microns by collecting images of the Raman scattering at wavelengths corresponding to the signature peaks of the observed phases. Reference Raman spectra of the major phases observed in the BSCCO system are also reported. The Raman techniques, when combined with complementary techniques, such as x-ray diffraction and electron microscopy, can provide valuable information about the reaction paths and mechanisms of the high temperature BSCCO superconducting ceramics.

Research over the past years has shown that proton and ion irradiation can significantly improve pinning in second-generation (2G) HTS wire by producing highly engineered defects [1-3]. However, the enhancement in Jc usually comes with a cost of depression of critical temperature Tc. The degradation can be partially recovered by post-annealing process [4]. The film quality and superconducting properties can be improved by altering the oxygen disorder and nanoscale defects after annealing. Although irradiation defects have been studied over a full range of atomic, electronic structures and physical properties, a detailed atomic level TEM analysis on the annealing effects is still needed.

A sharp dip in critical current has been observed in the field dependence of the critical current I c of commercial American Superconductor Corporation (AMSC) second-generation high-temperature superconducting tapes on Ni-5%W substrates, when the field is applied parallel to the plane of the tape. The dip occurs centered at a nonzero field for one field polarity only-the polarity in which the Lorentz force in the superconductor is toward the substrate. The polarity for which the dip occurs changes with the sample orientation and current direction, remaining consistent with the direction of the Lorentz force relative to the substrate. Angle dependences of I c in these tapes are consistent with this effect, lacking the usual 180° periodicity when measured under magnetic field strengths matching that of the dip in the field dependence. These effects are not observed on otherwise identical tapes produced with nonmagnetic Ni-9%W substrates, indicating that the ferromagnetism of the substrate plays a determining role. A finite-element model shows that this asymmetrical dip occurs naturally as a result of field concentration in the magnetic substrate, leading to a significant perpendicular component of field in the superconductor at a particular nonzero field strength.

A scalable laser lithographic process has been used to striate second-generation high-temperature superconducting coated conductors manufactured with a rolling-assisted biaxially textured substrate and metal organic deposition process by American Superconductor Corporation to reduce ac losses for electric power applications. The process involves laser patterning a resist coating and etching, which can be scaled up for commercial production. The results show that the critical current, I-c, is not degraded for striation widths greater than 150 mu m and that the ac losses for the 150-mu m wide striations are reduced from the unpatterned 1-cm wide conductor by a factor of 15 for a 60-mT perpendicular peak magnetic field at 50 Hz.

A self-monitoring, SMART (RE) Ba2Cu3O7-x (REBCO) conductor has been created by integrating optical fibers into the solder fillet of the current REBCO conductor architecture. By interrogating the integrated optical fiber by Raleigh backscattering, a spectral shift signal as a function of time and position along the conductor is obtained. Due to the direct integration into the solder fillet, intimate, consistent contact between fiber and conductor is obtained, while the optical fiber is protected and does not take up any space in the magnet winding. Therefore, the SMART conductor enhances the benefits of the co-wound fiber approach and provides ultimate sensitivity and practicality. Several samples of SMART REBCO conductor have been manufactured and characterized. The strain self-sensing capabilities have been demonstrated as well as thermal perturbation detection and localization with 2.56mm spatial resolution. Results show that a key feature of the SMART conductor concerns its sensitivity to thermal perturbation; unlike in the case of a coil with co-wound optical fiber, the SMART REBCO sensitivity increases as the temperature decreases. A series of quench measurements have been performed, both on straight samples and on a pancake coil, at temperatures as low as 14.6 K. Using the data collected by the SMART REBCO during quench experiments, the temporal evolution of the size of a normal zone and the instantaneous normal zone propagation velocity have been calculated.

YBa2Cu3O7-delta coated conductors (CCs) have achieved high critical current densities (J(c)) that can be further increased through the introduction of additional defects using particle irradiation. However, these gains are accompanied by increases in the flux creep rate, a manifestation of competition between the different types of defects. Here, we study this competition to better understand how to design pinning landscapes that simultaneously increase J(c) and reduce creep. CCs grown by metal organic deposition show non-monotonic changes in the temperature-dependent creep rate, S(T). Notably, in low fields, there is a conspicuous dip to low S as the temperature (T) increases from similar to 20 to similar to 65 K. Oxygen-, proton-, and Au-irradiation substantially increase S in this temperature range. Focusing on an oxygen-irradiated CC, we investigate the contribution of different types of irradiation-induced defects to the flux creep rate. Specifically, we study S(T) as we tune the relative density of point defects to larger defects by annealing both an as-grown and an irradiated CC in O-2 at temperatures T-A = 250 degrees C-600 degrees C. We observe a steady decrease in S(T > 20 K) with increasing T-A, unveiling the role of pre-existing nanoparticle precipitates in creating the dip in S(T) and point defects and clusters in increasing S at intermediate temperatures.