American Superconductor (United States)

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−δ coated conductors. A sequence of fluences covering the range from 1 × 1015 to 5 × 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.

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 × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">11</sup> ions/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> 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.

Abstract The variability and intermittency of the output from wind and solar generating facilities does not allow for consistent predictions of power generation that electric grid operators can use to ensure reliable and resilient electric service to meet the system demand. Dispatchability is commonly considered as the extent to which the resource (i.e., demand or supply resource) can be relied on to “follow a target” in relation to its load or generation. Variable renewable energy (VRE) or intermittent renewable energy sources (IRES) are renewable energy sources that are not dispatchable due to their fluctuating and intermittent nature, such as wind power and solar power, as opposed to dispatchable renewable energy sources such as hydroelectric, or fossil and nuclear baseloaded plants.

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. REBa <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> Cu <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">7</sub> (REBCO) coated conductors typically exhibit a large peak in critical current when the field is aligned with the REBCO <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">a</i> - <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">b</i> plane. The commercial pinning-enhanced American Superconductor Corporation (AMSC) REBCO coil wire used for this study is unusual in having a relatively small <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">a</i> - <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">b</i> 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 <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">a</i> - <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">b</i> plane peak. Complementary <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</i> -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 primary objectives of the Phase I Project was to develop a proof-of-principle for a concept of integrating an optical fiber sensor into the laminated 2G wire, there by producing a functionalized 2G wire with self-monitoring capabilities

The ability of high-temperature superconductors (HTSs) to carry very large currents with almost no dissipation makes them irreplaceable for high-power applications. The development and further improvement of HTS-based cables requires an in-depth understanding of the superconducting vortex dynamics in presence of complex pinning landscapes. We present a critical current analysis of a real HTS sample in a magnetic field by combining state-of-the-art large-scale Ginzburg-Landau simulations with reconstructive three-dimensional scanning transmission electron microscopy tomography of the pinning landscape in Dy-doped YBa$_2$Cu$_3$O$_{7-\delta}$. This methodology provides a unique look at the vortex dynamics in the presence of a complex pinning landscape, responsible for the high current-carrying capacity characteristic of commercial HTS wires. Our method demonstrates very good functional and quantitative agreement of the critical current between simulation and experiment, providing a new predictive tool for HTS wires design.

We demonstrate that 3.5-MeV oxygen irradiation can markedly enhance the in-field critical current of commercial second generation superconducting tapes with an exposure time of just 1 s per 0.8 cm2. The speed demonstrated here is now at the level required for an industrial reel-to-reel post-processing. The irradiation is made on production line samples through the protective silver coating and does not require any modification of the growth process. From TEM imaging, we identify small clusters as the main source of increased vortex pinning.