Caracterização de fitas supercondutoras 2G HTS em regime de Flux flow

According to the power law, the exponential factor (N) describes the V-I curve rise during the superconductor transition to the normal state. Moreover, N is important for the evaluation of the existing forces in the pinning mechanisms. It is an essential input parameter for the simulations of a wide range of applications such as coils, Superconducting Fault Current Limiters (SFCL) and other cases where the power law applies. This work explores experimental techniques based on the transport method and Four Lead configuration to obtain the N behavior of Second Generation High Temperature Superconductor (2G HTS) tapes beyond the Flux Creep regime. Since the value of N is extremely sensitive to the HTS tape temperature, the attention was held for ways to minimize the tape temperature oscillation during V-I measurements. First, a special copper sample holder was designed for utilizing the four probes measurement without the need of any soldered terminals, avoiding local degradation. The holder was also intended to serve as a thermal anchor, improving heat exchange in order to guarantee thermal stability. In addition, a homemade fast current source was created to apply current pulses with low duty cycle in order to reduce the thermal losses due to the significant resistance near and above critical current (Ic) values. Also, a pre-amplifier circuit was developed for continuous monitoring of voltage rise in the samples during the current pulse. The exponential factor N characteristics were obtained from V-I measurements for four 2G tapes models from different companies in self-field and liquid nitrogen bath. At last, the explored experimental techniques were used for the construction of a dry cooling current lead.De acordo com a lei de potência, o fator exponencial (N) descreve a elevação da curva V-I durante a transição do supercondutor para o estado normal. É um parâmetro de entrada essencial para simulação de uma ampla gama de aplicações tais como bobinas, Limitadores de Corrente Supercondutores (LCS) e outros casos em que a lei de potência se aplica. Este trabalho explora técnicas experimentais baseadas no método de transporte e na configuração de quatro pontas para obter o comportamento N de fitas supercondutoras de alta temperatura de segunda geração (2G HTS) além do regime Flux Creep. Como o valor de N é extremamente sensível à temperatura da fita HTS, a atenção foi mantida para maneiras de minimizar a oscilação da temperatura da fita durante as medições de V-I. Primeiro, foi projetado um suporte de amostra de cobre especial para a utilização da medição de quatro pontas sem a necessidade de qualquer terminal soldado, evitando a degradação local. O suporte também foi concebido para servir de âncora térmica, melhorando a troca de calor de modo a garantir a estabilidade térmica. Além disso, criou-se uma fonte caseira de corrente rápida para aplicar pulsos de corrente com baixo ciclo de trabalho para reduzir as perdas térmicas devido à resistência significativa próxima e acima dos valores críticos de corrente (Ic). Foi desenvolvido também um circuito de préamplificação para monitorização contínua da subida de tensão nas amostras durante os pulsos de corrente. As características dos fatores exponenciais N foram obtidas a partir de medidas de V-I para quatro modelos de fitas 2G de diferentes empresas em auto campo e banho de nitrogênio líquido. Por final, utilizou-se as técnicas experimentais de caracterização exploradas para projetar e executar um conceito de current leads refrigerado sem fluido criogênico

Enhanced normal zone propagation velocity in REBCO coated conductors using an intermetallic stabilizer coating

ABSTRACT: The Current Flow Diverter (CFD) is an established concept that has proven to effectively reduce the probability of destructive hot spots by boosting the normal zone propagation velocity (NZPV) in commercial REBa₂Cu₃O₇ (REBCO; RE = Rare Earth) coated conductors (CC). However, incorporating the CFD concept requires finding a scalable method that is also compatible with the already established R2R fabrication process used by CC manufacturers. This study presents a new simple & cost-effective proof-of-concept technique capable of recreating the CFD architecture in commercial CCs coated with silver. The technique is based on promoting a locally controlled thin film diffusion reaction between the silver stabilizer and pure indium. Due to fast diffusion in the Ag-In system, stable Intermetallic Compounds (IMC) are formed throughout the whole thickness of the silver layer reaching the REBCO interface. The presence of Ag-In IMC in the interface safely increases the interfacial resistance (Ω-cm²) by orders of magnitude, thus allowing to safely form the CFD interlayer. Silver-coated tape samples altered using this CFD-IMC have shown an NZPV increase of 5-8x when compared with pristine samples

Chemical Solution Deposition of Insulating Yttria Nanolayers as Current Flow Diverter in Superconducting GdBa2Cu3O7-δ Coated Conductors

The primary benefit of a metallic stabilization/shunt in high temperature superconductor (HTS) coated conductors (CCs) is to prevent joule heating damage by providing an alternative path for the current flow during the HTS normal state transition (i.e., quench). However, the shunt presence in combination with unavoidable fluctuations in the critical current (I c) of the HTS film can develop a localized quench along the CC's length if the operational current is kept close to I c. This scenario, also known as the hot-spot regime, can lead to the rupture of the CC if the local quench does not propagate fast enough. The current flow diverter (CFD) is the CC architecture concept that has proven to increase the conductor's robustness against a hot-spot regime by simply boosting the quench velocity in the CC, which avoids the shunt compromise in some applications. This work investigates a practical manufacturing route for incorporating the CFD architecture in a reel-to-reel system via the preparation of yttrium oxide (Y2O3) as an insulating thin nanolayer (∼100 nm) on top of a GdBa2Cu3O7 (GdBCO) superconductor. Chemical solution deposition (CSD) using ink jet printing (IJP) is shown to be a suitable manufacturing approach. Two sequences of the experimental steps have been investigated, where oxygenation of the GdBCO layer is performed after or before the solution deposition and the Y2O3 nanolayer thermal treatment formation step. A correlated analysis of the microstructure, in situ oxygenation kinetics, and superconducting properties of the Ag/Y2O3/GdBCO trilayer processed under different conditions shows that a new customized functional CC can be prepared. The successful achievement of the CFD effect in the case of the preoxygenated customized CC was confirmed by measuring the current transfer length, thus demonstrating the effectiveness of the CSD-IJP as a processing method.We acknowledge the funding of this research by FASTGRID Project (EU-H2020, 721019); the Projects COACHSUPENERGY (MAT2014-51778-C2-1-R) and SUMATE (RTI2018-095853-BC21 and RTI2018-095853-B-C22) from the Spanish Ministry of Economy and Competitiveness, which were cofunded by the European Regional Development Fund; and the Project 2017-SGR 753 from Generalitat de Catalunya and the COST Action NANOCOHYBRI (CA16218). ICMAB authors also acknowledge the Center of Excellence awards Severo Ochoa SEV-2015-0496 and CEX2019-000917-SWith funding from the Spanish government through the ‘Severo Ochoa Centre of Excellence’ accreditation (CEX2019-000917-S).Peer reviewe

Normal zone propagation in various REBCO tape architectures

The normal zone propagation velocity (NZPV) of three families of REBCO tape architectures designed for superconducting fault current limiters and to be used in high voltage direct current transmission systems has been measured experimentally in liquid nitrogen at atmospheric pressure. The measured NZPVs span more than three orders of magnitude depending on the tape architectures. Numerical simulations based on finite elements allow us to reproduce the experiments well. The dynamic current transfer length (CTL) extracted from the numerical simulations was found to be the dominating characteristic length determining the NZPV instead of the thermal diffusion length. We therefore propose a simple analytical model, whose key parameters are the dynamic CTL, the heat capacity and the resistive losses in the metallic layers, to calculate the NZPV.The authors acknowledge the funding of this research by FASTGRID Project (EU-H2020, 721019), the Projects COACHSUPENERGY (MAT2014-51778-C2-1-R), SUMATE (RTI2018-095853-BC21 and RTI2018-095853-B-C22) from the Spanish Ministry of Economy and Competitiveness which were cofunded by the European Regional Development Fund, the Project 2017-SGR 753 from Generalitat de Catalunya and the COST Action NANOCOHYBRI (CA16218). Polytechnique Montréal authors also acknowledge NSERC (Canada), FRQNT (Québec), the RQMP infrastructure and CMC microsystems for financial support. ICMAB authors also acknowledge the Center of Excellence awards Severo Ochoa SEV-2015-0496 and CEX2019-000917-S.With funding from the Spanish government through the ‘Severo Ochoa Centre of Excellence’ accreditation (CEX2019-000917-S).Peer reviewe

Development of High Temperature Superconductors Coated Conductors for Resistive Fault Current Limiters with the Current Flow Diverter Architecture

The primary benefit of a metallic stabilization/shunt in 2nd Generation (2G) High Temperature Superconductors (HTS) coated conductors (CC) is to prevent damage during quench by providing an alternative path for the current flow. On the downside, the increase in thermal capacity of a thick shunt makes the CCs prone to heat amassing due to hot-spots coming from variations in the critical current distribution of the HTS layer. This thermal issue makes the classical HTS tape design extremely vulnerable for operating in superconducting devices like high-field magnets and Superconducting fault Current Limiters SFCL. In SFCL, a prospective fault current level close to these tape's average critical current (Ic) can lead to destructive hot-spots in a matter of milliseconds. The Current Flow Diverter (CFD) is a promising multilayer architecture concept that has proven to increase the conductor's robustness against the inevitable hot-spot regime by inserting a high resistive layer partially covering the interface between the metallic silver shunt and the (Re)BCO film, thus alleviating shunt compromise. This relatively simple change creates a boost in the so-called Normal Zone Propagation Velocity (NZPV) and avoids the destructive heat amassing of hot-spots. However, since 2014 there has been a struggle in finding a practical manufacturing method compatible with the coating steps of reel-to-reel systems used by companies. In the framework of the H2020 project FASTGRID, this thesis reports on the technical journey of trying to achieve a feasible cost-effective method for implementing the CFD architecture in 12 mm wide 2G HTS tapes. Using chemical solution deposition (CSD) and chemical vapor deposition (CVD) methods, four materials, i.e epoxy, graphite, yttria and silver sulfide, led to four different manufacturing routes that helped identify the main practical constrains of the CFD fabrication and, for the first time, two viable CFD fabrication routes were found with yttria nanolayers and silver sulfidation reactions. Furthermore, for tapes with and without CFD, the Ic and NZPV, together with the maximum fault limitation conditions, electric field and fault time, were measured and compared using transport current in DC and AC respectively to confirm the advantages of the new proposed architectures

Transient liquid assisted growth of superconducting YBa2Cu3O7−x films based on pulsed laser deposition

We investigated the integration of transient liquid-assisted growth (TLAG) approach for epitaxial YBa2Cu3O7−x (YBCO) films by physical deposition methodologies (pulsed laser deposition (PLD)), as an additional opportunity for high-throughput growth of YBCO. As a prerequisite, highly flat and amorphous YBCO precursor films were deposited by PLD at temperatures below 400 °C on single-crystalline SrTiO3 (STO) and LaMnO3 (LMO)/STO, as well as industrial coated conductor architectures. Contrary to TLAG based on chemical solution deposition, where BaCO3 elimination is a key factor for the YBCO growth, TLAG-PLD growth is controlled by the transformation of Ba-Cu-O (s) to a transient liquid. High-quality c-axis YBCO films were successfully grown on different substrates, as demonstrated by high-resolution x-ray diffraction and transmission electron microscopy. In-situ resistance measurements revealed that the growth rates around 1000 nm s−1 can be achieved, outperforming the capabilities of standard PLD growth of REBa2Cu3O7 films by few orders of magnitude. Experimental conditions such as temperature, oxygen partial pressure, and heating ramp, were optimized to obtain critical temperature (T c) values up to 90 K. Critical current densities of 15 MA cm−2 at 5 K and 1.7 MA cm−2 at 77 K were obtained for YBCO films of 450 nm on LMO/STO.The authors acknowledge European Research Council for the ULTRASUPERTAPE project (ERC-2014-ADG-669504), IMPACT project (ERC-2019-PoC-874964) and SMS-INKS project (ERC-2022-PoC-101081998), as well as the EU COST actions CA16218 (NANOCOHYBRI), CA20116 (OPERA) and CA21144 (SUPERQUMAP). We also thank financial support from the Spanish Ministry of Economy and Competitiveness, and Spanish Ministry of Science, Innovation and Universities through the 'Severo Ochoa' Programme for Centres of Excellence in R&D (SEV-2015-0496 and CEX2019-000917-S), FUNFUTURE-FIP-2020-DATOPTICON, SUPERENERTECH project (PID2021-127297OB-C21), and SUMATE project (RTI2018-095853-B-C21, co-financed by the European Regional Development Fund). We also acknowledge support from the Catalan Government with 2017-SGR-1519 and the Catalan energy network XRE4S (2018 XARDI 00002). A Q thanks the Spanish Ministry of Science, Innovation and Universities for his 'Juan de la Cierva' postdoctoral fellowship (Grant No. IJC2018-035034-I). L S acknowledges financial support from Spanish Ministry of Science, Innovation and Universities through the FPI grants PRE2019-090621. Dr Silvia Rasi and Dr Roxana Vlad are thanked for fruitful discussions. We acknowledge the Scientific Services at ICMAB and ICN2 Electron Microscopy Division. Authors also acknowledge the use of instrumentation as well as the technical advice provided by the National Facility ELECMI ICTS, node 'Laboratorio de Microscopías Avanzadas' at University of Zaragoza. SuNAM Co. is acknowledged for providing metallic substrates.With funding from the Spanish government through the ‘Severo Ochoa Centre of Excellence’ accreditation (CEX2019-000917-S).Peer reviewe