Pareto-Optimization of HTS CICC for High-Current Applications in Self-Field

The ENEA superconductivity laboratory developed a novel design for Cable-in-Conduit Conductors (CICCs) comprised of stacks of 2nd-generation REBCO coated conductors. In its original version, the cable was made up of 150 HTS tapes distributed in five slots, twisted along an aluminum core. In this work, taking advantage of a 2D finite element model, able to estimate the cable's current distribution in the cross-section, a multiobjective optimization procedure was implemented. The aim of optimization was to simultaneously maximize both engineering current density and total current flowing inside the tapes when operating in self-field, by varying the cross-section layout. Since the optimization process involved both integer and real geometrical variables, the choice of an evolutionary search algorithm was strictly necessary. The use of an evolutionary algorithm in the frame of a multiple objective optimization made it an obliged choice to numerically approach the problem using a nonstandard fast-converging optimization algorithm. By means of this algorithm, the Pareto frontiers for the different configurations were calculated, providing a powerful tool for the designer to achieve the desired preliminary operating conditions in terms of engineering current density and/or total current, depending on the specific application field, that is, power transmission cable and bus bar systems

MOD derived pyrochlore films as buffer layer for all-chemical YBCO coated conductors

We report a detailed study performed on La2Zr2O7 (LZO) pyrochlore material grown by Metal-Organic Decomposition (MOD) method as buffer layers for YBa2Cu3O7-x (YBCO) coated conductors. High quality epitaxial LZO thin films have been obtained on single crystal (SC) and Ni-5%at.W substrates. In order to evaluate structural and morphological properties, films have been characterized by means of X-ray diffraction analyses (XRD), atomic force microscope (AFM) and scanning electron microscope (SEM). Precursors solutions and heat treatments have been studied by thermogravimetric analyses (TG-DTA-DTG) and infrared spectra (FT-IR) with the aim of optimizing the annealing process. Thin films of YBCO have been deposited by pulsed laser ablation (PLD) on this buffer layers. The best results obtained on SC showed YBCO films with critical temperature values above 90 K, high self field critical current density values (Jc > 1 MA/cm2) and high irreversibility field values (8.3 T) at 77 K together with a rather high depinning frequency vp (0.5 T, 77 K)>44 GHz as determined at microwaves. The best results on Ni-5%at.W has been obtained introducing in the heat treatment a pyrolysis process at low temperature in air in order to remove the residual organic part of the precursor solution

Effect of annealing on structure and superconducting properties in Fe(Se,Te)

Abstract In this paper, the effect of post synthesis annealing treatments on a Fe(Se,Te) polycrystalline material is evaluated and discussed. The samples have been obtained via melting route. The material has been subjected to a high-temperature annealing treatment, carried out for 45 h at 680 °C. The role of the cooling step was investigated comparing samples obtained after a controlled cooling or after quenching in liquid nitrogen. From a morpho-structural point of view, the annealing treatment improves homogeneity, with respect to pristine samples, and influences secondary phase precipitate morphology. Regarding superconducting properties, a key role of the cooling procedure is assessed: controlled cooling leads in fact to a significant improvement of high field behaviour with respect to the melted material, while quenched samples are characterized by a worsening of the superconducting properties. Despite the overall worsening, however, the quenched samples show evidence of the presence of superconducting phases characterized by a remarkably high critical temperature (Tc > 18 K), observed for these materials only in films or under pressure

Ionic liquid gating of ultra-thin YBa₂Cu₃O_7−x films

In this paper, we present a detailed investigation of the self-field transport properties of an ionic liquid gated ultra-thin YBa2Cu3O7−x (YBCO) film. From the high temperature dynamic of the resistivity (>220 K), different scenarios pertaining to the interaction between the liquid and the thin film are proposed. From the low temperature evolution of J c and T c, a comparison between the behavior of our system and the standard properties of YBCO is drawn

2D Numerical Simulations of HTS Cable-in-Conduit Conductor Cables

International audienceAmong the designs of high-temperature superconducting (HTS) cables considered for fusion magnet applications, the Twisted Stacked Tape Cable-in-Conduit-Conductor (TSTC-CICC) has gained considerable interest due to its easy manufacturing process, very high tape length usage, and flexibility capabilities. Over the past decade, ENEA has launched several experimental campaigns aimed primarily at studying the electromechanical capabilities of these TSTC-CICCs. In order to clarify different aspects of the experimental results, we have developed a 2D finite element (FE) model based on the recently proposed T-A formulation. The simulations have been implemented using a commercial FE analysis, solver and multiphysics simulation software. Such FE model includes the contact resistance of the electrical terminations used to inject the current and takes into account the angular dependence of the critical current on the local magnetic field. This 2D model allows to reproduce the experimental V-I results obtained in TSTC-CICCs with excellent agreement. Furthermore, the numerical simulations have allowed to deepen the understanding of those mechanisms that govern the current distribution inside the cable. The numerical model will be used to analyze the ac losses of a fully energized cable, to improve the capabilities of existing designs and to find an optimal configuration

2D Numerical Simulations of HTS Cable-in-Conduit Conductor Cables

International audienceAmong the designs of high-temperature superconducting (HTS) cables considered for fusion magnet applications, the Twisted Stacked Tape Cable-in-Conduit-Conductor (TSTC-CICC) has gained considerable interest due to its easy manufacturing process, very high tape length usage, and flexibility capabilities. Over the past decade, ENEA has launched several experimental campaigns aimed primarily at studying the electromechanical capabilities of these TSTC-CICCs. In order to clarify different aspects of the experimental results, we have developed a 2D finite element (FE) model based on the recently proposed T-A formulation. The simulations have been implemented using a commercial FE analysis, solver and multiphysics simulation software. Such FE model includes the contact resistance of the electrical terminations used to inject the current and takes into account the angular dependence of the critical current on the local magnetic field. This 2D model allows to reproduce the experimental V-I results obtained in TSTC-CICCs with excellent agreement. Furthermore, the numerical simulations have allowed to deepen the understanding of those mechanisms that govern the current distribution inside the cable. The numerical model will be used to analyze the ac losses of a fully energized cable, to improve the capabilities of existing designs and to find an optimal configuration

Measurement of Vortex Pinning in YBCO and YBCO/BZO Coated Conductors Using a Microwave Technique

In order to study the effect of pinning in coated conductors, we have used pulsed laser ablation to grow YBa2Cu3O7-x (YBCO) and YBa2Cu3O7-x/BaZrO3 (YBCO/BZO) films on metallic templates. Despite the complexity of the structure, after the optimization of the deposition procedure, the YBCO/BZO showed only a moderate reduction of Tc with respect to the pure YBCO sample. We use a very high frequency (∼47.7 GHz) dielectric resonator technique in order to induce very short distance vortex shaking, thus probing the steepness of the potential well. We report on measurements of the microwave response of the superconducting structures in terms of the quality factor Q and the frequency resonance ν0 as a function of a moderate dc magnetic field H, at different temperatures T. To keep as much contact as possible to the raw data (Q and ν0), in agreement with a generalized model for vortex dynamics, we determine the pinning parameter r and the upper limit for the creep factor χM. Based on the field dependence of the pinning parameters, the vortex pinning regimes were discussed. We find that the improvement of pinning by BZO is much reduced with respect to the effect observed in films grown on single crystals. In particular, the reduction of the critical temperature must be taken into account in order to appreciate the results

Effect of BaZrO3 Inclusions on the Microwave Surface Impedance of YBCOFilms in a Magnetic Field

We perform measurements of high-frequency (similar to 48 GHz) microwavesurface impedance with an applied magnetic field in YBa2Cu3O7-delta (YBCO) laser-ablated films with various amounts of BaZrO3 ( BZO)sub-micrometric inclusions, up to 7 mol % concentration. BZO inclusionsare very effective in the reduction of the field-induced surfaceresistance in our experimentally accessible field range [ 0, 0.8] T. Attemperatures low enough, the application of a moderate (similar to 0.2T) field makes the YBCO/BZO films markedly less dissipative than pureYBCO. This result, examined in the light of the very high measuringfrequency ( very small vortex oscillation amplitude) shows that BZOinclusions are even more effective pinning centers than columnardefects. We study the dependence of the vortex parameters ( vortexviscosity, pinning constant) on the BZO concentration. We examine thecorrelation between the reduction of the microwave dissipation and theareal density of BZO-induced defects. We argue that the very improvedperformances in a magnetic field are due to individual pinning ofvortices on BZO inclusions