A high-temperature superconducting (HTS) cable-in-conduit conductor (CICC) suitable for high-field magnet applications and comprised of twisted-stacked coated-conductor tapes arranged around a helically slotted core has been recently proposed and tested, demonstrating full compatibility with existing cabling technologies. To form the desired shape of any coils for high-field magnet applications, any suitable CICC option needs to be bent. For a magnet design, it is then very important to characterize the bending behavior of the CICC and, in particular, to find the smallest bending radius achieved without performance degradation. To this aim, bending tests were carried out on 1-m-long dummy samples of five helical slots in an extruded aluminum core, in which four REBCO tapes and dummy stainless-steel tapes were mounted in each slot. A controlled bending moment has been applied to the HTS CICC samples at room temperature, and each individual superconducting tape has been electrically characterized as a function of bending radius by measuring the critical current and n-index values at 77 K in a self-field condition. Results are analyzed and explained with the help of a three-dimensional cable model implemented in ANSYS and analytical calculations. The experimental and numerical results presented in this paper will demonstrate that the twisted-stack slotted-core technology can meet the bending requirements of high-field magnet designs.

ENEA is currently involved in the design and manufacture of a fully high temperature superconductor (HTS) cable in the cable-in-conduit conductor (CICC) configuration exploiting commercial second generation ReBaCuO (Re: Rare Earth and Y) coated-conductors. The final cable will be composed of five slots obtained in a helically twisted aluminum central core and filled with 2G tape stacks. This conductor is designed to operate above 10 kA in 12 T background field at 4.2 K or at about 10 kA in self-field at 77 K. A first sample of about 1-m length with one fully superconductive slot has been manufactured using 15 tapes provided by Superpower, Inc. and 12 tapes from the SuNAM Company grouped in two sub-stacks divided by a Kapton foil. Each tape of the stack has been characterized individually by measuring critical current values I_c at 77 K (liquid N₂ bath) in self-field and n-index. Results revealed that the tapes showed no degradation of critical current values when compared with suppliers specifications confirming that the proposed manufacturing process is fully compatible with commercial coated-conductors. Inter-tape resistance(R_inter) has also been measured and the observed dependence of R_inter on the tape position in the stack has been put in correlation with transverse stress distribution calculated by finite element models. A second sample with a full superconducting slot has been manufactured using 18 SuNAM tapes. Preliminary results on the stack transport measurements performed at 77 K in self-field will be presented and discussed. All the samples were manufactured by using already existing industrial equipments at Tratos Cavi SpA.

In this paper, we present a detailed investigation of the self-field transport properties of an ionic liquid gated ultra-thin YBa₂Cu₃O_7−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.

The introduction of artificial pinning sites in ${\text{YBa}}_2{\text{Cu}}_3{\text{O}}_{7-\delta }$ (YBCO) epitaxial thin films has been obtained by pulsed laser deposition (PLD) technique from YBCO-${\text{BaZrO}}_3$ (BZO) composite targets with BZO concentration ranging from 2.5 to $7\text{mol}\mathrm{\%}$ . The typical critical temperature, $T_c$ , drop observed in YBCO-secondary phase films grown by PLD has been successfully recovered by increasing the deposition temperature. Transport properties analyses revealed improved pinning force values for YBCO-BZO films for BZO concentration above $5\text{mol}\mathrm{\%}$ . These films exhibited an anomalous dual peak structure which has been ascribed to the presence of two pinning contributions. The crossover field, $B_m$ , separating these two pinning regimes has been observed to be temperature independent suggesting the occurrence of the matching field effect. The measured value of $B_m$ agreed with the matching field value, $B_{\Phi }=K{n}_d{\Phi }_0$ , as evaluated from transmission electron microscopy investigations. The mark of this phenomenon is retained down to 10 K, making YBCO-BZO more performing than pristine YBCO films at applied magnetic fields below $B_m$ in all the temperature range inspected. On the contrary, in the high magnetic field range (above $B_m$ ), the effectiveness of correlated pinning is progressively reduced on lowering the temperature suggesting that at low temperatures the dominant pinning contribution arises from isotropic pinning centers.

Pulsed laser deposited thin Y Ba₂Cu₃O_7−x (YBCO) films with pinning additions of 5 at. % Ba₂Y TaO₆ (BYTO) were compared to films with 2.5 at. % Ba₂Y TaO₆ + 2.5 at. % Ba₂Y NbO₆ (BYNTO) additions. Excellent magnetic flux-pinning at 77 K was obtained with remarkably high irreversibility fields greater than 10 T (YBCO-BYTO) and 11 T (YBCO-BYNTO), representing the highest ever achieved values in YBCO films.

We observe a strong reduction of the field induced thin film surface resistance measured at high microwave frequency $(\nu =47.7\mathrm{GHz})$ in $\mathrm{Y}{\mathrm{Ba}}_2{\mathrm{Cu}}_3{\mathrm{O}}_{7-\delta }$ thin films grown on $\mathrm{Sr}\mathrm{Ti}{\mathrm{O}}_3$ substrates, as a consequence of the introduction of submicrometric $\mathrm{Ba}\mathrm{Zr}{\mathrm{O}}_3$ particles. The field increase of the surface resistance is smaller by a factor of $\sim 3$ in the film with $\mathrm{Ba}\mathrm{Zr}{\mathrm{O}}_3$ inclusions, while the zero-field properties are not much affected. Combining surface resistance and surface reactance data, we conclude (a) that $\mathrm{Ba}\mathrm{Zr}{\mathrm{O}}_3$ inclusions determine very deep and steep pinning wells and (b) that the pinning changes nature with respect to the pure film.