Search

For an accurate estimation of the AC losses of superconducting triaxial cables, we present a 2D model capable to provide a global assessment of multi-layer triaxial cables, validated against the AC-losses on single-phase cables provided by the VNIIKP Cable Institute. Four models are presented, the first being a single-phase cable of 50 tapes and the others being three triaxial cables made of up to 135 coated conductors distributed in up to 9 layers. A systematic study is devised, where the number of layers per phase increases from 1 to 3, with at least 14 tapes distributed across each layer of the first (innermost) phase, 15 in the secondary (middle) phase, and 16 in the third (outermost) phase, respectively. Remarkably, our results reveal that the simple strategy of considering an unbalanced distribution for the amplitudes of the applied current, can generally balance the magnetic field between the three phases even for the bilayer and trilayer cables, resulting in negligible magnetic leaks in all situations. Besides, our simulations allow to see for the first time how the transport and magnetization currents distribute across the thickness of all the superconducting tapes, from which we have found that the AC-losses of the 2nd phase is generally higher than at the other phases at low to moderate transport currents Itr < 0.8 Ic. Nevertheless, depending on whether the Ic of the SC tapes at the 3rd phase layers is lower than the one at the 2nd phase, the layers at the third phase can exhibit a considerable increment on the AC losses, as result of the considered magneto angular anisotropy of the HTS tapes, which lead to intriguing electromagnetic features that suggest a practical threshold for the applied transport current, being it 0.8 Ic. Likewise, the relative change in the AC-losses per adding layers, per phase, and as a function of the applied current is disclosed., Comment: 13 pages, 6 figures, 1 supplementary figure included

With the recent progresses on the designing and manufacturing of lightweight and high engineering current density superconducting cables, the need for an established, fast, and sufficiently accurate computational model for the forecasting of AC-losses in cold-dielectric conductors, is pivotal for increasing the investment confidence of power grid operators. However, validating such models is not an easy task, this because on the one hand, there is a low availability of experimental results for large scale power cables and, on the other hand, there is a large number of 2G-HTS tapes involved whose cross-sectional aspect ratio hinders the numerical convergence of the models within reasonable delivery times. Thus, aiming to overcome this challenge, we present a detailed two-dimensional H-model capable to reproduce the experimentally measured AC-losses of multi-layer power cables made of tens of 2G-HTS tapes. Two cable designs with very high critical currents have been considered, the first rated at 1.7 kA critical current, consisting of fifty 4 mm width 2G-HTS tapes, these split in 5 concentric layers wound over a cylindrical former, with the three inner layers forming an arrangement of 24 tapes shielded by two further layers with 13 tapes each. This cable is contrasted with a size wise equivalent cable with 67 superconducting tapes rated at 3.2 kA critical current, whose design implies the use of 40 tapes of 3 mm width split within four core layers, and 27 tapes of 4 mm width distributed in two shielding layers. In both situations a remarkable resemblance between the simulations and experiments has been found, rendering to acceptable estimates of the AC-losses for cold dielectric conductors, and offering a unique view of the local electrodynamics of the wound tapes where the mechanisms of shielding, magnetization, and transport currents can coexist within the hysteretic process., Comment: 4 Figures, 6 pages

A better understanding of the interaction between three phases is required when developing superconducting cables for high voltage AC systems. With a particular focus on the energy losses of real power transmission cables, in this paper we utilize the so-called H-formulation of Maxwell equations to devise a 2D model for superconducting triaxial cables. The major aim of this model is to comprehend and reproduce the experimental observations reported on the first triaxial prototype cable developed by SuperOx and VNIIKP. The computationally modelled and prototyped cable is made of up to 87 tapes of 4 mm width SuperOx tape arranged across the three phases. Our computational results are compared to the experimental measurements performed by VNIIKP with the electrical contact method, showing a high degree of accuracy over the outer phase of the cable, whilst revealing technical issues with the experimental measurements at the inner phases. Thus, in consultation with VNIIKP it has been concluded that for the actual experimental measurement of the AC losses at the inner phases, and consequently of the overall cable, a sophisticated calorimetric setup must be built. Still our model is capable to provide an independent assessment of the VNIIKP-SuperOx cable design, by investigating the magnetic profiles per phase in the time domain. In this sense, we confirm that the unbalanced arrange of currents and distancing between the phases affirmatively lead to no magnetic leakages, and therefore to an adequate balance of the cabling inductance., Comment: 9 pages, 3 figures, CEC/ICMC'21 Conference, IOP Conference Series: Materials Science and Engineering, Advances in Cryogenic Engineering (Accepted, Ref. M3Po1A-03, 11 January 2022)

The Conductor on Rounded Core (CORC) cables manufactured by Advanced Conductor Technologies with current densities beyond 300 Amm^-2 at 4.2 K, and bending diameter of up to 3.5 cm, are considered as one of the strongest candidates for the next generation of high field power applications and magnets. In this paper, we present a full 3D FEM model for their monolayer and bilayer CORC cables made with up to three and six superconducting tapes respectively, disclosing the full curve of AC losses for the monolayer cable at magnetic fields beyond 60 mT, and the actual distribution of current density along and across the thickness of the superconducting tapes in both designs. The model is based on the so-called H-formulation, allowing to incorporate the true three-dimensionality of the tapes without recurring to 2D thin-film approaches where non-physical surface currents that do not follow the celebrated Bean's model for type-II superconductors appear. Likewise, good agreement with the experimentally measured AC-losses for the monolayer and bilayer cable have been obtained, with all the details of the model disclosed in this paper., Comment: Manuscript Accepted at IEEE Transactions on Applied Superconductivity 18 January 2022. Submitted 20 September 2021. his work was supported by the UK Research and Innovation, Engineering and Physical Sciences Research Council (EPSRC), through the grant Ref. EP/S025707/1 led by H.S.R

Conductor on a rounded core (CORC\textsuperscript{\textregistered}) cables with current densities beyond 300 A/mm$^{-2}$ at 4.2 K, and a capacity to retain around 90 $\%$ of critical current after bending to a diameter of 3.5 cm, make them a strong candidate for high field power applications and magnets. In this paper, we present a full 3D-FEM model based upon the so-called H-formulation for commercial CORC\textsuperscript{\textregistered} cables manufactured by Advanced Conductor Technologies LLC. The model presented consists of tapes ranging from 1 up to 3 SuperPower 4mm-width tapes in 1 single layer and at multiple pitch angles. By varying the twist pitch, local electromagnetic characteristics such as the current density distribution along the length and width are visualized. Measurements of macroscopical quantities such as AC-losses are disclosed in comparison with available experimental measurements. We particularly focused on the influence of the twist pitch by comparing the efficiency and performance of multiple cables, critically assessing the optimal twist pitch angle., Comment: 9 pages, 3 figures, CEC/ICMC'21 Conference, IOP Conference Series: Materials Science and Engineering, Advances in Cryogenic Engineering

Improving our understanding of the physical coupling between type-II superconductors (SC) and soft ferromagnetic materials (SFM), is root for progressing onto the application of SC-SFM metastructures in scenarios such as magnetic cloaking, magnetic shielding, and power transmission systems. However, in the latter some intriguing and yet unexplained phenomena occurred, such as a noticeable rise in the SC energy losses, and a local but not isotropic deformation of its magnetic flux density. These phenomena, which are in apparent contradiction with the most fundamental theory of electromagnetism for superconductivity, i.e., the critical state theory (CST), have remained unexplained for about 20 years, given place to the acceptance of the controversial and yet paradigmatic existence of the so-called overcritical current densities. Therefore, aimed to resolve these long-standing problems, we extended the CST by incorporating a semi-analytical model for cylindrical monocore SC-SFM heterostructures, setting the standards for its validation with a variational approach of multipole functionals for the magnetic coupling between Sc and SFM materials. It is accompanied by a comprehensive numerical study for SFM sheaths of arbitrary dimensions and magnetic relative permeabilities $\mu_{r}$, ranging from $\mu_{r}=5$ (NiZn ferrites) to $\mu_{r}=350000$ (pure Iron), showing how the AC-losses of the SC-SFM metastructure radically changes as a function of the SC and the SFM radius for $\mu_{r} \geq 100$. Our numerical technique and simulations revealed also a good qualitative agreement with the magneto optical imaging observations that were questioning the CST validness, proving therefore that the reported phenomena for self-field SC-SFM heterostructures can be understood without including the ansatz of overcritical currents., Comment: 14 pages, 5 figures

A reliable tool for site-suitability assessment of solar power plants capable to account for the sustainable development and protection of cultural and biodiversity conservation areas is proposed. We present a novel Analytic Hierarchy Process (AHP) based approach for the Multi-Decision Criteria Analysis (MDCA) of SSI satellite retrieved data and local information sources, it within a GIS platform tailored to fit the needs of energy stakeholders at Indonesia, simultaneously ensuring the conservation of legally protected areas. This imposes significant challenges due to the wide diversification of cultural, natural, and ecological protected areas that need to be considered, in landmarks that demand for high resolution imaging of surface solar irradiance (SSI) within $\pm 4^{\circ}$ of the equator. To overcome these challenges, a GIS spatial weighted overlay analysis for criteria layers such as climatology, topography, electrical grid, and road infrastructure has been performed, it based on the technical and economic feasibility for solar plants deployment within three approximation schemes focused on their proximity to the existing (i) power network, (ii) road infrastructure, and (iii) community settlements. Here, we focused on the West Kalimantan Province of Borneo Island (WKP), it mainly due to its possibility of onshore inter-connectivity and energy share with Malaysia and Brunei, and the high national and international importance that brings forward the protection of the biodiversity of Borneo. It has been found that the optimal location of PV plants can be reduced to just $0.03\%$ ($46.60~km^{2}$) and $0.07\%$ ($108.58~{km}^{2}$) of WKP, in what we report as the best-suitable conditions out of the $33.05\%$ exploitable area found after the exclusion of conservation areas. This corresponds to ..., Comment: This work was supported by the Institutional Links grant, ID 413871894, under the Newton Fund Indonesia partnership. The grant is funded by the UK Department for Business, Energy and Industrial Strategy and the Indonesian Ministry of Research, Technology, Higher Education and delivered by the British Council. For further information, please visit www.newtonfund.ac.uk

A noteworthy physical dependence of the hysteresis losses with the axial winding misalignment of superconducting racetrack coils made with commercial \textcolor{black}{Second Generation High Temperature Superconducting (2G-HTS)} tapes is reported. A comprehensive study on the influence of the turn-to-turn misalignment factor on the local electromagnetic properties of individual turns, is presented by considering six different coil arrangements and ten amplitudes for the applied alternating transport current, $I_{a}$, together with an experimentally determined function for the magneto-angular anisotropy properties of the critical current density, $J_{c}(B,\theta)$, across the superconducting tape. It has been found that for moderate to low applied currents $I_{a} \leq 0.6~I_{c0}$, with $I_{c0}$ the self-field critical current of individual tapes, the resulting hysteretic losses under extreme winding deformations can lead to an increase in the energy losses of up to $25\%$ the losses generated by a perfectly wound coil. High level meshing considerations have been applied in order to get a realistic account of the local and global electromagnetic properties of racetrack coils, .... Our findings can be used as a practical benchmark to determine the relative losses for any 2G-HTS racetrack coil application, unveiling the physical fingerprints that possible coil winding misalignments could infer., Comment: 19 pages, 5 figures. Submitted AIP 16-Apr-2019 05:02:38

In the past few years there has been a significant rise in the short-circuit current levels in transmission and distribution networks, it due to the increasing demands on power and the addition of sources of distributed generations. It leads to the need of integration of novel protection systems such as the superconducting fault current limiters (SFCLs), ... . SFCL models on the electric distribution networks largely rely on the insertion of a step or exponential resistance that is determined by a predefined quenching time. However, beyond the framework of these models, the study of the performance, reliability, and location strategy for the installation of sole or multiple SFCLs in power grids still lacks of proper development leading to the utter need of comprehensive and systematic studies on this issue. In this paper, we expand the scope of the aforementioned models by considering the actual behaviour of a SFCL in terms of the temperature dynamic power-law dependence between the electrical field and the current density. Our results are compared with step-resistance models for the sake of discussion and clarity of the conclusions. Both SFCL models were integrated into a power system model built based on the UK power standard, and the impact of these protection strategies on the performance of the overall electricity network was studied. As a representative renewable energy source, a 90 MVA wind farm was considered for the simulations. Three fault conditions have been simulated, and the figures for the fault current reduction predicted by both fault current limiting models have been compared in terms of multiple current measuring points and allocation strategies...

Contents Preface I Electromagnetism of type II superconductors 1 General Statements Of The Critical State 1.1 The CS In The Maxwell Equations Formalism 1.2 The CS Regime And The MQS Limit 2 Variational Theory for CS Problems 2.1 General Principles Of The Variational Method 2.2 The Material Law: SCs with magnetic anisotropy 2.2.1 Onto the 1D Critical States 2.2.2 Towards The 3D Critical States 3 Computational Method Conclusions I References I II Critical State Problems:Effects & Applications 4 Type-II SCs With Intrinsic Magnetic Anisotropy 4.1 3D variational statement in slab geometry 4.2 Isotropic predictions in -3D- configurations 4.3 T-states in -3D- configurations 4.4 CT-states in -3D- configurations 4.5 Smooth critical states in -3D- configurations Appendix I Critical angle gradient in -3D- configurations 5 The Longitudinal Transport Problem 5.1 Simplified analytical models and beyond 5.1.1 The simplest analytical model 5.1.2 The SDCST statement and the BM's approach 5.2 Magnetic anisotropy and the uncommon effects 5.2.1 Extremal case: The T-states model 5.2.2 Material laws with magnetic anisotropy: CT\chi - models 6 Electromagnetism For Superconducting Wires 6.1 Theoretical framework and general considerations 6.2 SC wires subjected to isolated external sources 6.2.1 Wires with an injected AC transport current 6.2.2 Wires under an external AC magnetic flux 6.2.3 Ultimate considerations on the AC losses 6.3 SC wires under simultaneous AC excitations (B_{0},I_{tr}) 6.3.1 Synchronous excitations 6.3.2 Asynchronous excitations Conclusions II References II Supplementary Material II III Microscopical aspects also analyzed 7 E-Ph Theory And The Nodal Kink Effect In HTSC 8 Is it necessary to go beyond the E-Ph mode? Conclusions III References III Supplementary Material III IV Addenda, Comment: Dissertation Condensed Matter Physics Department of University of Zaragoza, Materials Science Institute of Arag\'on (ICMA), The Spanish National Research Council (CSIC). Cite together arXiv code as: http://hdl.handle.net/10261/46732 Digital CSIC open science: Dissertations ICMA

Relying on our theoretical approach for the superconducting critical state problem in 3D magnetic field configurations, we present an exhaustive analysis of the electrodynamic response for the so-called longitudinal transport problem in the slab geometry. A wide set of experimental conditions have been considered, including modulation of the applied magnetic field either perpendicular or parallel (longitudinal) to the transport current density. The main objective of our work was to characterize the role of the macroscopic material law that should properly account for the underlying mechanisms of flux cutting and depinning. The intriguing occurrence of negative current patterns and the enhancement of the transport current flow along the center of the superconducting sample are reproduced as a straightforward consequence of the magnetically induced internal anisotropy. Moreover, we show that related to a maximal projection of the current density vector onto the local magnetic field, a maximal transport current density occurs somewhere within the sample. The elusive measurement of the flux cutting threshold (critical value of such parallel component $J_{c ||}$) is suggested on the basis of local measurements of the transport current density. Finally, we show that a high correlation exists between the evolution of the transport current density and the appearance of paramagnetic peak structures in terms of the applied longitudinal magnetic field., Comment: Submitted. 18 pages, 12 figures. The quality of some figures have been adjusted to the arXiv requirements

Numerical simulations of filamentary type II superconducting wires under simultaneous AC transport current and oscillating transverse magnetic fields are performed within the critical state approximation. The time dependences of the current density profiles, magnetic flux lines, local power dissipation and magnetic moment are featured. Noticeable non-homogeneous dissipation and field distortions are displayed. Also, significant differences between the obtained AC-losses and those predicted by regular approximation formulas are reported. Finally, an outstanding low pass filtering effect intrinsic to the magnetic response of the system is described., Comment: Submitted. 9 pages + 1 page with a movie caption. Additional material (movies) have been uploaded to the Data Conservancy Pilot Project of arXiv repositories. Also, this and more videos are available to download in: http://www.unizar.es/departamentos/fisica_mat_condensada/people/hsruizr/

Several aspects of the general theory for the critical states of a vortex lattice and the magnetic flux dynamics in type-II superconductors are examined by a direct variational optimisation method and widespread physical principles. Our method allows to unify a number of conventional models describing the complex vortex configurations in the critical state regime. Special attention is given to the discussion of the relation between the flux-line cutting mechanism and the depinning threshold limitation. This is done by using a smooth double critical state concept which incorporates the so-called isotropic, elliptical, T and CT models as well-defined limits of our general treatment. Starting from different initial configurations for a superconducting slab in a 3D magnetic field, we show that the predictions of the theory range from the collapse to zero of transverse magnetic moments in the isotropic model, to nearly force free configurations in which paramagnetic values can arbitrarily increase with the applied field for magnetically anisotropic current voltage laws. Noteworthily, the differences between the several model predictions are minimal for the low applied field regime., Comment: 12 pages, 4 figures (Best quality pictures are available by author's contact), Submitted on May 27, 2010

The longitudinal transport problem (the current is applied parallel to some bias magnetic field) in type-II superconductors is analyzed theoretically. Based on analytical results for simplified configurations, and relying on numerical studies for general scenarios, it is shown that a remarkable inversion of the current flow in a surface layer may be predicted under a wide set of experimental conditions. Strongly inhomogeneous current density profiles, characterized by enhanced transport toward the center and reduced, or even negative, values at the periphery of the conductor, are expected when the physical mechanisms of flux depinning and consumption (via line cutting) are recalled. A number of striking collateral effects, such as local and global paramagnetic behavior, are predicted. Our geometrical description of the macroscopic material laws allows a pictorial interpretation of the physical phenomena underlying the transport backflow., Comment: 8 pages, 6 figures (Best quality pictures are available by author's contact)

Despite the intensive efforts for determining the mechanism that causes high-temperature superconductivity in copper oxide materials, no consensus on the pairing mechanism has been reached. Recent advances in high resolution angle-resolved photoemission spectroscopies have suggested that a sizeable electron-phonon coupling exists as the principal cause for kinks in the dispersion relations (energy versus wave vector) of the electronic states. Here, we report on a systematic study about the influence of the electron-phonon coupling parameter "$\lambda$" in the electronic quasiparticle dispersions along the nodal direction for $La_{2-x}Sr_{x}CuO_{4}$, $Bi_{2}Sr_{2}CaCu_{2}O_{8+x}$ and $YBa_{2}Cu_{3}O_{6+x}$. Information about the dressing of the charge carriers, i.e., on the enhancement of the effective mass and the strength of the coupling mode, is obtained as a function of the doping concentration, temperature, momentum and energy from the kink dispersion in the (0-0)-$(\pi,\pi)$ direction of momentum-space avoiding the complications of the \textit{d-}wave superconducting gap. Our analysis shows a remarkable agreement between theory and experiment for different samples and at different doping levels. This includes our recently introduced theoretical model to adjust the experimental data of the fermionic band dispersion, emphasising the necessary distinction between the general electron mass-enhancement parameter $\lambda^{*}$ and the conventional electron-phonon coupling parameter $\lambda$., Comment: Submitted

The magnetic flux dynamics of type-II superconductors within the critical state regime is posed in a generalized framework, by using a variational theory supported by well established physical principles. The equivalence between the variational statement and more conventional treatments, based on the solution of the differential Maxwell equations together with appropriate conductivity laws is shown. Advantages of the variational method are emphasized, focusing on its numerical performance, that allows to explore new physical scenarios. In particular, we present the extension of the so-called double critical state model to three dimensional configurations in which only flux transport (T-states), cutting (C-states) or both mechanisms (CT-states) occur. The theory is applied to several problems. First, we show the features of the transition from T to CT states. Second, we give a generalized expression for the flux cutting threshold in 3-D and show its relevance in the slab geometry. In addition, several models that allow to treat flux depinning and cutting mechanisms are compared. Finally, the longitudinal transport problem (current is applied parallel to the external magnetic field) is analyzed both under T and CT conditions. The complex interaction between shielding and transport is solved., Comment: 21 figures, submitted for publication

The experimental finding of an ubiquitous kink in the nodal direction of angle-resolved photoemission spectroscopies of superconducting cuprates has been reproduced theoretically. Our model is built upon the Migdal-Eliashberg theory for the electron self-energy within the phonon-coupling scenario. Following this perturbative approach, a numerical evaluation of the bare band dispersion energy in terms of the electron-phonon coupling parameter $\lambda$ allows a unified description of the nodal-kink effect. Our study reveals that distinction between $\lambda$ and the technically defined mass-enhancement parameter $\lambda^{*}$ is relevant for the quantitative description of data, as well as for a meaningful interpretation of previous studies. A remarkable agreement between theory and experiment has been achieved for different samples and at different doping levels. The full energy spectrum is covered in the case of LSCO, Bi2212 and overdoped Y123. In the case of underdoped Y123, the model applies to the low energy region (close to Fermi level)., Comment: Accepted to PRB Vol. 79 Issue 5 (Feb-2009). 20 pages, 4 figures. ARPES, Kink, Electron-Phonon coupling, Mass-enhancement parameter