Article

# Double disordered YBCO coated conductors of industrial scale: High currents in high magnetic field

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## Abstract

A significant increase of critical current in high magnetic field, up to 31 T, was recorded in long tapes manufactured by employing a double-disorder route. In a double-disordered high-temperature superconductor (HTS), a superimposing of intrinsic and extrinsic disorder takes place in a way that (i) the intrinsic disorder is caused by local stoichiometry deviations that lead to defects of crystallinity that serve as pining centers in the YBa2Cu3Ox−δ matrix and (ii) the extrinsic disorder is introduced via embedded atoms or particles of foreign material (e.g. barium zirconate), which create a set of lattice defects. We analyzed possible technological reasons for this current gain. The properties of these tapes over a wider field-temperature range as well as field anisotropy were also studied. Record values of critical current as high as 309 A at 31 T, 500 A at 18 Tm and 1200 A at 5 T were found in 4 mm wide tape at 4.2 K and B perpendicular to tape surface. HTS layers were processed in medium-scale equipment that allows a maximum batch length of 250 m while 22 m long batches were provided for investigation. Abnormally high ratios (up to 10) of critical current density measured at 4.2 K, 19 T to critical current density measured at 77 K, self-field were observed in tapes with the highest in-field critical current. Anisotropy of the critical current as well as angular dependences of n and α values were investigated. The temperature dependence of critical current is presented for temperatures between 4.2 and 40 K. Prospects for the suppression of the dog-bone effect by Cu plating and upscale of processing chain to >500 m piece length are discussed.

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... To a large extent, the advanced currents are due to large concentration of local defects of crystallinity generated in DD-HTS coated tapes. High in-field critical currents gained by DD-like architectures in comparison with alternative HTS nano-architectures [1,2] made a substantial impact to recent progress in upgraded technologies of long HTS coated tapes [3,4] based on pulsedlaser-deposition (PLD) [5,6]. In 2017, the EUROTAPES EC project was successfully finalized in large part thanks to a PLD progress at Bruker resulted in processing of >500 m long HTS coated tapes (project goal) [6][7][8]. ...
... Substantial progress was done in this direction also by Bruker HTS in the recent past. A significant increase of critical current in the high magnetic field, up to 31 T, was observed in tapes manufactured by employing a double-disorder (DD) route [3,8] which creates a set of lattice defects [12][13][14] in the HTS layer. ...
... HTS layers with double disordered structure were deposited via pulsed laser deposition (PLD) technique onto metallic substrate tapes [3] coated with yttria-stabilized zirconia (YSZ) template fabricated using an alternating-beam-assisted deposition (ABAD) [14] and, finally, with ceria (CeO 2 ) cap layer [3,15]. The ABAD-YSZ layer fabricated with a thickness of 1.7-2.6 μm represented a template with in-plane texture which corresponds to a full-width at half-maximum (FWHM) of 9°-10° (phi-scan). ...
Article
Full-text available
Double disordered (DD) HTS layers processed via high-fluence PLD with modulated pressure and barium zirconate precipitation yield very high engineering current densities, above 900 and 600 A/mm 2 at 18 and 31 T, respectively, measured at 4.2 K and B||c. Tape architecture is based on 50-100-μm-thick polished stainless steel tape which prior to DD-HTS deposition was coated with YSZ template yielding a biaxial in-plane texture with FWHM = 10-11° characterized using phi-scan XRD technique. High-resolution nanostructural analysis indicated a number of nonusual features in DD YBCO layers regarding “firework”-like orientation of nanoprecipitations /nanochains. These new features result in a very high concentration of local defects which reduce the critical current (I c ) measured at 77 K, self-field to about 30% of the corresponding I c in non-DD YBCO, and simultaneously lead to substantial gaining of Ic at high fields. The main result is a substantial improvement of Ic and engineering current density (J e ) achieved at high field and liquid Helium temperature in long length, large area tapes with 4 and 12 mm width. J e above 970 A/mm 2 at 4.2 K, B = 18 T, B||c was achieved in 12-mm-wide tape.
... The reduction of substrate thickness in the employed tape design (as shown in figure 1 to achieve this goal seems to be the simplest. In reality, with a 50 μm thick substrate, major core steps in the employed processing route, such as alternating beam-assisted deposition (ABAD) [6] and pulsed laser deposition (PLD) [3,7,8] must be re-tuned because of a substantial variation of mechanical and thermal parameters of a thin substrate. ...
... ABAD [6] was employed for deposition of a bi-axially textured yttria-stabilized zirconia (YSZ) buffer layer, typically 2-3 μm thick. PLD is based on a drum-supported tape with equilibrium heating of the tape via hot wall reactor positioned in the deposition zone [3,8]. Further details of PLD including a discussion of mechanisms determined growth of double disordered (DD) superconducting layers [3] based on YBa 2 Cu 3 O 7−δ can be found in [8]. ...
... PLD is based on a drum-supported tape with equilibrium heating of the tape via hot wall reactor positioned in the deposition zone [3,8]. Further details of PLD including a discussion of mechanisms determined growth of double disordered (DD) superconducting layers [3] based on YBa 2 Cu 3 O 7−δ can be found in [8]. The final steps of tape manufacture include enveloping of the tape with a 1-2 μm thick silver layer deposited via thermal vacuum evaporation and metallization; the final steps of tape fabrication are described in [7,8]. ...
... solution growth or metal-organic deposition(MOD)) in which several Figure 15 shows transmission electron microscopy (TEM) images of a REBCO film containing BaZrO 3 nanorods. Their geometry makes them ideal pinning sites, particularly in aligned magnetic fields, and indeed, in recent years remarkable advances in performance of research-scale REBCO CCs has been achieved by increasing the Zr-content (Selvamanickam et al 2013, Xu et al 2014, Abraimov et al 2015, Selvamanickam et al 2015a, 2015c, 2015d and perfecting the structure of the BZO nanorods (Selvamanickam et al 2015d). Strong pinning by correlated, i.e. anisotropic, pinning sites, such as these BZO nanorods, leaves characteristic fingerprints in the angular dependence of J c , ( ) θ J c . ...
... With decreasing temperature, the maximum in ( ) θ J c due to BZO nanorods becomes less pronounced, and the overall anisotropy of J c , that is, the ratio of the maximum and minimum values in θ J c ( ), decreases, until at 30 K θ J c ( ) is almost independent of angle. The strong isotropic pinning seen in figure 16 at low temperatures has been attributed to the presence of nanoparticles residing between the nanorods (Abraimov et al 2015, Selvamanickam et al 2015a and to strain fields (Gutierrez et al 2007, Xu et al 2012 as the lattice mismatch between BaZrO 3 and REBCO is large, ∼8%. Extensive work on solution-grown YBCO films has shown that strain-fields associated with nano-particles can give rise to strong isotropic pinning (Gutierrez et al 2007, Puig et al 2008, Llordés et al 2012. ...
... Measurements at 64 K and 4 T following neutron-irradiation of chemical vapor deposited films showed a pronounced dip of J c around the in-plane directions (Chudy et al 2015). The angular dependence of J c depends sensitively on temperature, field, defect structure, and balance between isotropic and aniso tropic pinning (Civale et al 2004, MacManus-Driscoll et al 2004, Goyal et al 2005, Matsumoto et al 2005, Yamada et al 2005, Puig et al 2008, Maiorov et al 2009, Palau et al 2011, Selvamanickam et al 2012, Choi et al 2013, Abraimov et al 2015, Mishev et al 2015. Thus, further investigations on carefully characterized sample are required in order to fully understand the evolution with irradiation. ...
Article
The behavior of vortex matter in high-temperature superconductors (HTS) controls the entire electromagnetic response of the material, including its current carrying capacity. Here, we review the basic concepts of vortex pinning and its application to a complex mixed pinning landscape to enhance the critical current and to reduce its anisotropy. We focus on recent scientific advances that have resulted in large enhancements of the in-field critical current in state-of-the-art second generation (2G) YBCO coated conductors and on the prospect of an isotropic, high-critical current superconductor in the iron-based superconductors. Lastly, we discuss an emerging new paradigm of critical current by design-a drive to achieve a quantitative correlation between the observed critical current density and mesoscale mixed pinning landscapes by using realistic input parameters in an innovative and powerful large-scale time dependent Ginzburg-Landau approach to simulating vortex dynamics.
... The reduction of substrate thickness in the employed tape design (as shown in figure 1 to achieve this goal seems to be the simplest. In reality, with a 50 μm thick substrate, major core steps in the employed processing route, such as alternating beam-assisted deposition (ABAD) [6] and pulsed laser deposition (PLD) [3,7,8] must be re-tuned because of a substantial variation of mechanical and thermal parameters of a thin substrate. ...
... ABAD [6] was employed for deposition of a bi-axially textured yttria-stabilized zirconia (YSZ) buffer layer, typically 2-3 μm thick. PLD is based on a drum-supported tape with equilibrium heating of the tape via hot wall reactor positioned in the deposition zone [3,8]. Further details of PLD including a discussion of mechanisms determined growth of double disordered (DD) superconducting layers [3] based on YBa 2 Cu 3 O 7−δ can be found in [8]. ...
... PLD is based on a drum-supported tape with equilibrium heating of the tape via hot wall reactor positioned in the deposition zone [3,8]. Further details of PLD including a discussion of mechanisms determined growth of double disordered (DD) superconducting layers [3] based on YBa 2 Cu 3 O 7−δ can be found in [8]. The final steps of tape manufacture include enveloping of the tape with a 1-2 μm thick silver layer deposited via thermal vacuum evaporation and metallization; the final steps of tape fabrication are described in [7,8]. ...
Article
Full-text available
Gaining engineering critical current density ( J e ) in high-temperature superconducting (HTS) coated conductors based on double-disordered YBCO for operation at high fields is one of the key requirements in upcoming magnet/accelerator projects. Currently, the development of a tape with advanced J e -s is performed based on an alternating beam-assisted deposition–pulsed laser deposition (ABAD–PLD) manufacturing route. An obvious way to improve J e -s is to reduce substrate thickness. A 40% J e increase is expected owing to the thickness reduction from 100 to 50 μ m. Nevertheless, the reduction of substrate thickness in case of the applied processing technology that employs relatively thick (2–3 μ m) yttria-stabilized zirconia buffer layers leads to the manifestation of considerable strain in the tape resulting in strong tape bowing. Advanced processing routes have been developed to suppress this effect. The highest engineering current density was recorded at well above 1000 A mm ⁻² under an ultra-high field of 18 T at 4.2 K, B // c . Influence of tape bowing and the impact of longitudinal defects are studied via V – I measurements at 77 K and a moderate magnetic field with intrinsic edge gradients. Potential for further gaining of J e was found employing mechanisms of (i) film nucleation from lateral flows that provide material transfer during the PLD process. Further steps include suppressing the instability of instantaneous temperature via quasi-adiabatic pulsed heating of the growing HTS film via (ii) control of laser plume energy, and (iii) energy release during film condensation (condensation enthalpy). These effects disturb the instantaneous temperature of the growing HTS layer, which exhibits very limited capability of heat transfer. Temperature pulses reaching 30–40 K were evaluated via heat transfer modeling. Stabilization of the level of pulsed temperature during layer growth is anticipated to result in a further increase in J e .
... REBCO coated tapes are gaining importance due to their outstanding performance in high and ultra-high magnetic fields [1][2][3] and their favorable mechanical stability [4]. Magnet applications dominate here [5,6], but also applications in accelerators/colliders [7] as well as in fusion technologies [8,9] are becoming essential. ...
... In this work, a relatively good correlation between critical currents at high fields, helium temperatures and the temperature of liquid nitrogen was found, when the characterization at 77 K is performed in a magnetic field of several Tesla. These studies were conducted with HTS coated tapes from various manufacturers, but not with tapes having a double-disordered (DD) structure [3], where 'intrinsic' and 'extrinsic' nano-precipitations [12] are introduced. ...
... Figure 6(a) shows the oscillogram of both, the voltage drop U(τ) in the tape (2) and the inverted current in the windings (1), which is proportional to the field, for a sample tape #5 with an 8 A current load. The field quickly builds up after switching of the magnet (τ=0 s) at a maximum rate of 16 T s −1 which is reached after 50-60 ms at 0.9 T. Thereby induced voltage is visible in the signal (3). ...
Article
Full-text available
A study of HTS-coated tapes which are exposed to a low and medium field with a gradient in the flux density is performed in order to enable relevant and accurate tape characterization as well as to determine the relevant information for applications, where a magnetic field gradient occurs. In particular, the study is focused on ultra-high-magnet-field YBCO-coated tapes. Such tapes based on double disordered YBCO layer with intrinsic and extrinsic precipitations exhibit a ‘champion’ performance in ultra-high (31 T) magnetic fields. Alternative measurement techniques, based on miniature permanent magnets or a pulsed electro-magnet was developed to characterize the critical current, I c , in 0.5 and 3 T fields at 77 K, B // c , respectively. For the field dependence of the critical current, an ‘extended alpha approximation’ is suggested, which enables a sufficiently accurate description of the tape behavior in the low and medium field range, i.e. from 0 to 6 T. Local and integral voltage response in the tapes are analyzed and compared with experimental results. Observations of the effect that gains the influence of local I c -inhomogeneities exposed to a spatially confined magnetic field are described and discussed. The effects of local heating and cooling are shown to be limited via lowering the transport currents and finally a reduced power dissipation in the tape exposed to a localized magnetic field with two gradient zones was demonstrated. Correction factors needed to determine the critical current from the field dependence of the integral voltage response are derived and discussed.
... The same limitation will apply to H-based superconductors as studies now focus on critical fields properties [8][9][10]. This limitation makes vortex pinning in superconductors at fields above 20 T almost uncharted territory [20][21][22][23][24]. So, a sensible pathway forward is to achieve J c measurements in pulsed magnetic fields [25][26][27], as peak fields up to 100 T are routinely achievable in the millisecond range at large facilities [28][29][30] and 30 T table-top systems are available [31]. ...
... The samples of Y 0.77 Gd 0. 23 metal-organic deposition (MOD) on CeO 2 capped IBAD-MgO metal substrates, following Miura et al. [34]. The nominal J c in self-field at 77 K on short samples were 5.3 and 5.0 MA/cm 2 , respectively. ...
Article
Nonlinear electrical transport studies at high pulsed magnetic fields, above the range accessible by dc magnets, are of direct fundamental relevance to the physics of superconductors, domain-wall, charge-density waves, and topological semimetal. All-superconducting very high field magnets also make it technologically relevant to study vortex matter in this regime. However, pulsed magnetic fields reaching 100 T in milliseconds impose technical and fundamental challenges that have prevented the realization of these studies. Here, we present a technique for sub-microsecond smart current-voltage measurements, which enables the determination of the superconducting critical current in pulsed magnetic fields, beyond the reach of any dc magnet. We demonstrate the excellent agreement of this technique with low dc field measurements on Y0.77Gd0.23Ba2Cu3O7 coated conductors with and without BaHfO3 nanoparticles. Exploring the uncharted high-magnetic-field region, we discover a characteristic influence of the magnetic field rate of change (dH/dt) on the current-voltage curves in a superconductor. We fully capture this unexplored vortex physics through a theoretical model based on the asymmetry of the vortex-velocity profile produced by the applied current.
... Significant enhancements of J c have been achieved with the incorporation of RE 2 O 3 [22,23], YBa 2 Cu 3 O 5 [24], and BaZrO 3 [25][26][27] nanoparticles. A major advance in the synthesis of highperformance REBCO-coated conductors was the discovery that under certain deposition conditions the addition of excess metal oxides such as BaZrO 3 [28][29][30][31][32][33][34][35][36][37][38], BaSnO 3 [39], or BaHfO 3 [40] results in the formation of self-assembled nanorods largely oriented along the c-axis of the YBCO structure with lengths of hundreds of nanometers and diameters of1 0 nm. Their geometry makes them ideal pinning sites, particularly in aligned magnetic fields, and indeed, in recent years, remarkable advances in performance of research-scale REBCO CCs has been achieved by increasing the Zr content and perfecting the structure of the BZO nanorods [33][34][35][36][37][38]. ...
... A major advance in the synthesis of highperformance REBCO-coated conductors was the discovery that under certain deposition conditions the addition of excess metal oxides such as BaZrO 3 [28][29][30][31][32][33][34][35][36][37][38], BaSnO 3 [39], or BaHfO 3 [40] results in the formation of self-assembled nanorods largely oriented along the c-axis of the YBCO structure with lengths of hundreds of nanometers and diameters of1 0 nm. Their geometry makes them ideal pinning sites, particularly in aligned magnetic fields, and indeed, in recent years, remarkable advances in performance of research-scale REBCO CCs has been achieved by increasing the Zr content and perfecting the structure of the BZO nanorods [33][34][35][36][37][38]. In short-length samples of highly doped REBCO conductors, critical current densities as high as 7 MA/cm 2 at 30 K and 9 T applied parallel to c-axis have been reported [35][36][37]. ...
Article
Full-text available
We present a perspective on a new critical-current-by-design paradigm to tailor and enhance the current-carrying capacity of applied superconductors. Critical-current-by-design is based on large-scale simulations of vortex matter pinning in high-temperature superconductors and has qualitative and quantitative predictive powers to elucidate vortex dynamics under realistic conditions and to propose vortex pinning defects that could enhance the critical current, particularly at high magnetic fields. The simulations are validated with controlled experiments and demonstrate a powerful tool for designing high-performance superconductors for targeted applications.
... REBCO tapes were mainly provided by Bruker HTS (BHTS), a member of the EuCARD2 consortium. While the development of other tape manufacturers was initially driven by the perspectives of applications in the electrical utility sector, the R&D program of BHTS was dedicated from its beginning to developing and producing long-length tapes for highresolution NMR spectrometers [29], whose targets in terms of high current density at high field and low temperature have considerable synergy with the requirements for accelerator magnets. Table 1 summarizes the targets and the minimum required performance for the REBCO tapes considered within the scope of EuCARD2 and ARIES. ...
... Substantial progress was made in this direction by BHTS. A significant increase in Jc in a high magnetic field was recorded in tapes manufactured employing the so-called double-disorder (DD) route [29,48,49], which creates intrinsic and extrinsic defects in the YBCO layer. The intrinsic disorder is caused by local stoichiometry deviations with respect to the nominal YBa2Cu3O7−x composition and is achieved through a tailored modulation of the oxygen pressure during the PLD process. ...
Article
Full-text available
In view of the preparation for a post-LHC collider, in 2010 the high-energy physics (HEP) community started to discuss various options, including the use of HTS for very high-field dipoles. Therefore, a small program was begun in Europe that aimed at exploring the possibility of using HTS for accelerator-quality magnets. Based on various EU-funded programs, though at modest levels, it has enabled the European community of accelerator magnet research to start getting experience in HTS and address a few issues. The program was based on the use of REBa2Cu3O7−x (REBCO) tapes to form 10 kA Roebel cables to wind small dipoles of 30–40 mm aperture in the 5 T range. The dipoles are designed to be later inserted in a background dipole field (in Nb3Sn), to reach eventually a field level in the 16–20 T range, beyond the reach of Low Temperature Superconductors (LTS). The program is currently underway: more than 1 km of high-performance tape (Je > 500 A/mm2 at 20 T, 4.2 K) has been manufactured and characterized, various 30 m long Roebel cables have been assembled and validated up to 13 kA, a few dipoles have been wound and tested, reaching 4.5 T in stand-alone (while a dipole made from flat race track coils exceeded 5 T using stacked tape cable), and tests in background field are being organized.
... Significant enhancements of Jc have been achieved with the incorporation of RE2O3 [21,22], YBa2Cu3O5 [23], BaZrO3 [24][25][26] nanoparticles. A major advance in the synthesis of high-performance REBCO coated conductors was the discovery that under certain deposition conditions the addition of excess metal oxides such as BaZrO3 [27][28][29][30][31][32][33][34][35][36][37], BaSnO3 [38] or BaHfO3 [39] results in the formation of self-assembled nanorods largely oriented along the c-axis of the YBCO structure with lengths of hundreds of nm and diameters of ~ 10 nm. Their geometry makes them ideal pinning sites, particularly in aligned magnetic fields, and indeed, in recent years, remarkable advances in performance of research-scale REBCO CCs has been achieved by increasing the Zr-content and perfecting the structure of the BZO nanorods [32][33][34][35][36][37]. ...
... A major advance in the synthesis of high-performance REBCO coated conductors was the discovery that under certain deposition conditions the addition of excess metal oxides such as BaZrO3 [27][28][29][30][31][32][33][34][35][36][37], BaSnO3 [38] or BaHfO3 [39] results in the formation of self-assembled nanorods largely oriented along the c-axis of the YBCO structure with lengths of hundreds of nm and diameters of ~ 10 nm. Their geometry makes them ideal pinning sites, particularly in aligned magnetic fields, and indeed, in recent years, remarkable advances in performance of research-scale REBCO CCs has been achieved by increasing the Zr-content and perfecting the structure of the BZO nanorods [32][33][34][35][36][37]. In short-length samples of highly doped REBCO conductors, critical current densities as high as 7 MA/cm 2 at 30 K and 9 T applied parallel to c-axis have been reported [34][35][36]. ...
Preprint
We present a perspective on a new critical-current-by-design paradigm to tailor and enhance the current-carrying capacity of applied superconductors. Critical current by design is based on large-scale simulations of vortex matter pinning in high-temperature superconductors and has qualitative and quantitative predictive powers to elucidate vortex dynamics under realistic conditions and to propose vortex pinning defects that could enhance the critical current, particularly at high magnetic fields. The simulations are validated with controlled experiments and demonstrate a powerful tool for designing high-performance superconductors for targeted applications.
... Nuclear fusion, medicine and pharmacology are among the areas of science that benefit from high magnetic field facilities [1]. The capacity of HTS material to maintain high critical currents under high magnetic fields has strongly stimulated the research towards a new generation of high-field magnets employing commercial HTS tapes [2]- [4]. The highest reported direct-current magnetic field is 45.5 T. This value was recently reached by a 14.4 T HTS test coil operated inside a 31.1 T resistive magnet [5]. ...
... Now, T is only defined inside the bulks and its computation does not take into account the influence of B z (the component parallel to the surface of the tapes). Therefore, T has only one component defined by (2). A detailed description of the T-A homogenous strategy can be consulted in [30]. ...
Article
The 32 T all-superconducting magnet of the National High Magnetic Field Laboratory (NHMFL) was successfully tested in December 2017 and it is expected to be soon available for users. This all-superconducting magnet, comprised of a high-temperature superconducting (HTS) insert and a low-temperature superconducting (LTS) outsert, is the first superconducting magnet reaching more than 30 T. One of the challenges facing this new magnet technology is the estimation of the screening currents, and the corresponding hysteresis losses in the two HTS coils. These coils are made of more than 20,000 turns of insulated REBCO conductor connected in series. The modelling of such system represents a significant challenge due to the huge computational load imposed by the size of the system. Up to now, only medium size magnets (made of units of thousands of turns/tapes) have been successfully modelled with methods based on the well-known H formulation of the Maxwell's equations. In the present work, a new model based on the T-A formulation and a homogeneous technique is proposed. This new approach greatly reduces the computational load and allows performing real-time simulations of large-scale HTS magnets on personal computers.
... Most recently, under a developing interest in high field applications, and thanks to the introduction of various pinning mechanisms (the most effective being BZO nanorods [19]), the performance at low temperature of industrially produced REBCO has progressed steadily. At 4.2 K and 20 T in perpendicular field, industrially produced REBCO has attained record values of J E in excess of 800 A/mm 2 [20], and the target performance of Table I was achieved by several production routes. In addition, the J E potential does not seem to be fully exploited [21]. ...
... The best results were achieved by introducing double-disorder in the YBCO layer. The extrinsic pinning obtained via precipitates of BZO in the form of nanorods, is complemented by intrinsic pinning created by intentional variation in the stoichiometry of the deposited layer [20]. It must be underlined that these tapes have a rather thick substrate, 100 μm of steel, and the reported values of J E correspond to a layer J C (4.2 K, 20 T) well exceeding 50 kA/mm 2 , which, to our knowledge, is the highest value reported to date for industrial tapes. ...
Article
Full-text available
The objective of the EuCARD2 WP10 (Future Magnets) research activity is to demonstrate high-temperature superconducting magnet technology for accelerator applications by building a short demonstrator dipole with an aperture of 40 mm, operating field of 5 T, and understood field quality. One of the magnet requirements is of small inductance, for use in long magnet strings; hence, the superconducting cable must have large current-carrying capacity, in the range of 10 kA at the operating conditions of 4.2 K and 5 T. An initial down-selection of the cable material and geometry resulted in the choice of REBCO tapes assembled in a Roebel cable as the baseline layout. In this paper, we described the requirements derived from magnet design, the selection process that led to the choice of material and geometry, the reference design of the cable, and its options. Activities have started to address fundamental issues, such as tape performance and tape processing through the cable construction, and key performance parameters such as cable critical current under stress or magnetization. Here, we report the main highlights from this work.
... REBCO tapes were mainly provided by Bruker HTS (BHTS), a member of the EuCARD-2 consortium. While the development of other tape manufacturers has been initially driven by the perspectives of applications in the electrical utility sector, the R&D program of BHTS was dedicated from its beginning to develop and produce long-length tapes for high resolution NMR spectrometers [29], whose targets in terms of high current density at high field and low temperature have a considerable synergy with the requirements for accelerator magnets. The targets and the minimum required performance for the REBCO tapes considered within the scope of EuCARD-2 and ARIES are reported in Table 1. ...
... Substantial progress was done in this direction by BHTS. A significant increase of Jc in high magnetic field was recorded in tapes manufactured employing the so-called double-disorder (DD) route [29,48,49], which creates intrinsic and extrinsic defects in the YBCO layer. The intrinsic disorder is caused by local stoichiometry deviations with respect to the nominal YBa2Cu3O7−x composition and is achieved through a tailored modulation of the oxygen pressure during the PLD process. ...
Preprint
In view of the preparation for a post-LHC collider, the high-energy physics (HEP) community started from 2010 to discuss various options, including the use of HTS for very high field dipoles. Therefore, a small program was set in Europe aiming at exploring the possibility of using HTS for accelerator quality magnets. Based on various EU funded programs, though at modest levels, has enabled the European community of accelerator magnets to start getting experience in HTS and addressing a few issues. The program was based on use of REBCO tapes to form 10 kA Roebel cables, to be used to wind small dipoles of 30-40 mm aperture in the 5 T range. The dipoles are designed to be later inserted in a background dipole field (in Nb3Sn), to reach eventually a field level in the 16-20 T range, beyond the reach of LTS. The program is currently underway: more than 1 km tape of high performance (Je > 500 A/mm2 at 20 T, 4.2 K has been manufactured and characterized, various 30 m long Roebel cables have been assembled and validated up to 13 kA, a few dipoles have been wound and tested, reaching at present 4.5 T in stand-alone (while a dipole made from race track coils with no-bore exceeded 5 T using stacked tape cable) and a test in a background field is being organized.
... A common approach to enhance J c in magnetic field has been to introduce artificial pinning centres (APC) of c-axis correlated nano-columns of various perovskites [21][22][23][24][25] , a technique utilised in commercial PLD 28,29,38 and metalorganic chemical vapour deposition (MOCVD) film growth 6 . Although the highest J c (B) values have been obtained in this way [39][40][41] , the complex HTS film nanostructure results in considerable spread in commercial wire in-field performance 26,27 and greatly narrows the processing window, requiring slower deposition rates to achieve maximum J c enhancement 28,29 . ...
... Samples were immersed in liquid helium during experiments at 4.2 K. Samples were in helium gas during experiments at 20 K 26 In experiments up to 31.2 T we used the NHMFL resistive magnet system (cell 7) with a 50 mm bore magnet; 38 mm in Janis cryostat. More experimental detail can be found in 38 . ...
Article
Full-text available
The fusion power density produced in a tokamak is proportional to its magnetic field strength to the fourth power. Second-generation high temperature superconductor (2G HTS) wires demonstrate remarkable engineering current density (averaged over the full wire), JE, at very high magnetic fields, driving progress in fusion and other applications. The key challenge for HTS wires has been to offer an acceptable combination of high and consistent superconducting performance in high magnetic fields, high volume supply, and low price. Here we report a very high and reproducible JE in practical HTS wires based on a simple YBa2Cu3O7 (YBCO) superconductor formulation with Y2O3 nanoparticles, which have been delivered in just nine months to a commercial fusion customer in the largest-volume order the HTS industry has seen to date. We demonstrate a novel YBCO superconductor formulation without the c-axis correlated nano-columnar defects that are widely believed to be prerequisite for high in-field performance. The simplicity of this new formulation allows robust and scalable manufacturing, providing, for the first time, large volumes of consistently high performance wire, and the economies of scale necessary to lower HTS wire prices to a level acceptable for fusion and ultimately for the widespread commercial adoption of HTS.
... There were quite some attempts to increase the thickness of the superconducting layer, but it is generally still below 2 μm in currently available long length conductors. The alternative approach to improve the critical current of a tape is the introduction of artificial pinning [13][14][15][16][17][18][19]. This was widely and successfully done during the past few years, by adding a large variety of secondary phases, which segregate into nano-scaled correlated or uncorrelated pinning centers, thus boosting the performance of coated conductors and helping to reduce their anisotropy. ...
... The optimal concentration of nanorods predicted for a REBCO conductor (Figure 2a) is approximately three to four times larger than the values observed in our experiments on currently available industrial samples containing 7.5 mol% Zr. Extensive recent work on research-scale samples has shown that the critical current density increases strongly with Zr-content , that is, with the concentration of nanorods, [27,39,[45][46][47][48]and samples with Zr-doping up to 25 mol% have been synthesized. Our simulations (Figure 2a) are aligned with these studies and suggest that there is still room for further enhancement. ...
Article
A new critical-current-by-design paradigm is presented. It aims at predicting the optimal defect landscape in superconductors for targeted applications by elucidating the vortex dynamics responsible for the bulk critical current. To this end, critical current measurements on commercial high-temperature superconductors were combined with large-scale time-dependent Ginzburg-Landau simulations of vortex dynamics.
... As noted above the lengthwise dependence of I c , I c (z), is of great importance for magnet use, especially at low temperatures where conductor current densities J E are several times higher than at 77 K and local overheating at 'bad' regions could be fatal to magnet performance. Although several manufacturers now manufacture CCs in lengths of 500-1500 m [18][19][20][21] no one is yet capable of delivering uniform lengths on this scale. For multiple reasons, mostly unreported in the open literature, tapes are cut into lengths of typically 50-200 m after the defect population is assessed by transport or magnetization methods. ...
Article
We present a broad study by multiple techniques of the critical current and critical current density of a small but representative set of nominally identical commercial RE123 (REBa2Cu3O7-δ, RE = rare Earth, here Y and Gd) coated conductors (CC) recently fabricated by SuperPower Inc. to the same nominal high pinning specification with BaZrO3 and RE2O3 nanoprecipitate pinning centers. With high-field low-temperature applications to magnet technology in mind, we address the nature of their tape-to-tape variations and length-wise Ic inhomogeneities by measurements on a scale of about 2 cm rather than the 5 m scale normally supplied by the vendor and address the question of whether these variations have their origin in cross-sectional or in vortex pinning variations. Our principal method has been a continuous measurement transport critical current tool (YateStar) that applies about 0.5 T perpendicular and parallel to the tape at 77 K, thus allowing variations of c-axis and ab-plane properties to be clearly distinguished in the temperature and field regime where strong pinning defects are obvious. We also find such in-field measurements at 77 K to be more valuable in predicting 4.2 K, high-field properties than self-field, 77 K properties because the pinning centers controlling 77 K performance play a decisive role in introducing point defects that also add strongly to Jc at 4.2 K. We find that the dominant source of Ic variation is due to pinning center fluctuations that control Jc, rather than to production defects that locally reduce the active cross-section. Given the 5-10 nm scale of these pinning centers, it appears that the route to greater Ic homogeneity is through more stringent control of the REBCO growth conditions in these Zr-doped coated conductors.
... Nb-Ti and Nb3Sn wires have been exclusively used in these applications. Recently significant progress has been made in doped RE-Ba-Cu-O (REBCO, RE=rare earth) superconductor tapes with superior in-field critical current performance at 4.2 K [3][4][5]. Engineering current densities (Je) as high as 1658 A/mm 2 have been achieved at 4.2 K, 21 T which is more than six times higher than that of Nb3Sn. Additionally, the superior mechanical property and high critical temperature of REBCO tapes make them a competitive candidate for high-field magnets which operate above 20 T or at a temperature higher than liquid helium. ...
Article
Using ultrathin RE-Ba-Cu-O (REBCO, RE=rare earth) superconductor tapes, we have fabricated of a multi-layer round wire with an outer diameter of 1.6 mm on a flexible copper former of 0.8 mm diameter with a critical current of 283 A at 77 K, self-field. A single-layer round wire’s angular dependence of critical current in a magnetic field shows near isotropic characteristics. The critical current of a single-layer round wire has been measured over a temperature range of 30 – 77 K in magnetic fields up to 9 T.
... To date, these conductors are fabricated using different deposition processes by different industrial manufacturers, and they can be expected to have significantly different transport properties. However, there has been limited research published on the lowtemperature high-field properties of REBCO conductors [8][9][10], and most of them are about special conductors that are under development [11][12][13][14]. Thus, we have developed a U-shaped sample holder that can be used in a commonly found high-field magnet and carried out critical current measurements of commercially available REBCO conductors in perpendicular magnetic fields of up to 18 T, at 4.2 K [15]. ...
Article
Full-text available
REBCO coated conductors are now available from several industrial manufacturers and are expected to be promising conductors for high-field-magnet applications. Using these conductors, the development of solenoids capable of generating high magnetic fields of 20–30 T is ongoing in major high-field laboratories in the world. In addition, CERN recently launched a conceptual design study for the Future Circular Collider, in which a 20-T dipole magnet is listed as a candidate for the bending magnet of the main ring. However, there has been limited research published on the electrical transport properties of commercially available REBCO conductors in a high-field, low-temperature environment. For magnet designers, the transport properties are of the highest importance in choosing a suitable conductor, and the data form the bases for high-field magnet development. Therefore, in this work, a new sample holder, which allows the measurements of full-width conductors to be carried out relatively easily, was developed, and the transport properties of commercial REBCO conductors from seven manufacturers (AMSC, Fujikura, Shanghai Superconductor, SuNAM, SuperOx, SuperPower, and SWCC Showa) were investigated at 4.2 K in perpendicular fields of up to 18 T. The results show that the Ic values at 4.2 K clearly vary to some extent among these commercial conductors and the higher-current 4-mm-wide conductors have Ic values in the range of 230–305 A at 18 T and in the range of 320–424 A at 12 T.
... [1][2][3][4] Generating strong artificial pinning centers (APCs) of desired morphology, dimension and concentration in HTS films and conductors has been a major focus of research during the past decade. [4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19] Exciting progress has been made via strain-mediated self-organization of nanoscale APCs of impurity phases in YBa 2 Cu 3 O 7δ (YBCO) thin films and conductors. [20][21][22] Among others, c-axis aligned one-dimensional APCs (1D-APCs) have exhibited strong correlated pinning to magnetic vortices at magnetic field H//c-axis, resolving the issue of weak pinning along the c-axis originated from the layered structure of the YBCO. ...
Article
Full-text available
An elastic strain model was applied to evaluate the rigidity of the c-axis aligned one-dimensional artificial pinning centers (1D-APCs) in YBa2Cu3O7-δ matrix films. Higher rigidity was predicted for BaZrO3 1D-APCs than that of the BaHfO3 1D-APCs. This suggests a secondary APC doping of Y2O3 in the 1D-APC/YBa2Cu3O7-δ nanocomposite films would generate a stronger perturbation to the c-axis alignment of the BaHfO3 1D-APCs and therefore a more isotropic magnetic vortex pinning landscape. In order to experimentally confirm this, we have made a comparative study of the critical current density Jc (H, θ, T) of 2 vol.% BaZrO3 + 3 vol.%Y2O3 and 2 vol.%BaHfO3 + 3 vol.%Y2O3 double-doped (DD) YBa2Cu3O7-δ films deposited at their optimal growth conditions. A much enhanced isotropic pinning was observed in the BaHfO3 DD samples. For example, at 65 K and 9.0 T, the variation of the Jc across the entire θ range from θ=0 (H//c) to θ=90 degree (H//ab) is less than 18% for BaHfO3 DD films, in contrast to about 100% for the BaZrO3 DD counterpart. In addition, lower α values from the Jc(H) ∼ H-α fitting were observed in the BaHfO3 DD films in a large θ range away from the H//c-axis. Since the two samples have comparable Jc values at H//c-axis, the improved isotropic pinning in BaHfO3 DD films confirms the theoretically predicted higher tunability of the BaHfO3 1D-APCs in APC/YBa2Cu3O7-δ nanocomposite films.
... µm thick film is lower than that of our 15% Zr-added ~0.9 μm thick film and higher than the ~3.0 μm 15% Zr-added sample 35 . The sample exhibits I c above 1 kA at H up to 13 T, well above all other reported values 37 . Taking into account the ~50 μm thick substrate and ~40 μm thick surround copper stabilizer layer in commercial REBCO tapes, J e of this 20% Zr-added ~3.2 μm thick REBCO film reaches 1 kA/mm 2 at H up to 31.2 T, a real threshold for compelling, cost-effective applications. ...
Article
Full-text available
A main challenge that significantly impedes REBa2Cu3Ox (RE = rare earth) coated conductor applications is the low engineering critical current density Je because of the low superconductor fill factor in a complicated layered structure that is crucial for REBa2Cu3Ox to carry supercurrent. Recently, we have successfully achieved engineering critical current density beyond 2.0 kA/mm² at 4.2 K and 16 T, by growing thick REBa2Cu3Ox layer, from ∼1.0 μm up to ∼3.2 μm, as well as controlling the pinning microstructure. Such high engineering critical current density, the highest value ever observed so far, establishes the essential role of REBa2Cu3Ox coated conductors for very high field magnet applications. We attribute such excellent performance to the dense c-axis self-assembled BaZrO3 nanorods, the elimination of large misoriented grains, and the suppression of big second phase particles in this ~3.2 μm thick REBa2Cu3Ox film.
... The way the deposition it is done, with a double disorder due to Barium Zirconate oxide (BZO) point and columnar defects, and with Yttria precipitates, enhance critical current at high field and low temperature [17]. The improvements of critical current was continuous along the four year of the process. ...
Article
The EuCARD2 collaboration aims at the development of a 10 kA-class superconducting, high current density cable suitable for accelerator magnets, to be tested in small coils and magnets capable to deliver 3-5 T when energized in stand-alone mode, and 15-18 T when inserted in a 12-13 T background magnet. REBCO tape, assembled in a Roebel cable, was selected as conductor. The developed REBCO tape has reached a record engineering critical current density, at 4.2 K and 18 T of 956 A/mm2. Roebel cable carried up to 13 kA at 20K when tested in a small coil (FeatherM0.4). Then a first dipole magnet, wound with two low grade Roebel cables of 25 m each, was assembled and tested. The dipole reached the short sample critical current of 6 kA generating more than 3 T central field at about 5.7 K, with indications of good current transfer among cable strands and of relatively soft transition. The construction of a costheta dipole is also discussed. Eucard2 is reaching its objective and is continuing with the H2020-ARIES program aiming at doubling the Je at 20 T to obtain 6 T as standalone and 18 T as insert in a high field facility.
... The current leads made it possible to input a current of up to 500 A for a short time and in a long-term (several minutes) mode up to 250 A without overheating them. The critical current of a standard HTSC-2G wire in self field in liquid helium is 10─15 times higher than in liquid nitrogen [7], and with a wire width of 4 mm it can reach 2000 A. Therefore, our experimental stand allowed direct measurements on samples with a high critical current only in liquid nitrogen. For measurements in liquid helium, samples with a low critical current at nitrogen temperature were used or, when measured using a fixed current method (see below), the current was reduced to an acceptable level. ...
Article
At present, HTSC-2G tape wires (hereinafter wires) are an uncontested basis for creating conductors for the magnetic system of a compact thermonuclear reactor. Since, according to calculations, the tangential mechanical stresses in the windings of its magnetic system can exceed 1000 MPa, the requirement for high electromechanical stability of the HTSC wire used comes first, which makes it possible to raise the constructive current density. In this work, comparative electromechanical test of HTSC-2G wires with different thicknesses of the superconducting layer, on a substrate made of AISI 310S stainless steel, at the temperature of liquid nitrogen and liquid helium were carried out. The factors leading to a decrease in the degradation of the critical current at high tensile stresses have been established. A new method for testing HTSC-2G wires at helium temperature and a simple method for preliminary assessment of their electromechanical properties at nitrogen temperature are proposed.
... The same limitation will apply for H-based superconductors as studies now focus on critical fields properties. [8][9][10] This limitation makes vortex pinning in superconductors at fields above 20 T almost uncharted territory [20][21][22][23][24]. So, a sensible pathway forward is to achieve J c measurements in pulsed magnetic fields [25][26][27], as peak fields up to 100 T are routinely achievable in the millisecond range at large facilities [28][29][30] and 30 T table-top systems are available. ...
Preprint
Full-text available
arXiv:1903.04658 : Non-linear electrical transport studies at high-pulsed magnetic fields, above the range accessible by DC magnets, are of direct fundamental relevance to the physics of superconductors, domain-wall, charge-density waves, and topological semi-metal. All-superconducting very-high field magnets also make it technologically relevant to study vortex matter in this regime. However, pulsed magnetic fields reaching 100 T in milliseconds impose technical and fundamental challenges that have prevented the realization of these studies. Here, we present a technique for sub-microsecond, smart, current-voltage measurements, which enables determining the superconducting critical current in pulsed magnetic fields, beyond the reach of any DC magnet. We demonstrate the excellent agreement of this technique with low DC field measurements on Y$_{0.77}$Gd$_{0.23}$Ba$_2$Cu$_3$O$_7$ coated conductors with and without BaHfO$_3$ nanoparticles. Exploring the uncharted high magnetic field region, we discover a characteristic influence of the magnetic field rate of change ($dH/dt$) on the current-voltage curves in a superconductor. We fully capture this unexplored vortex physics through a theoretical model based on the asymmetry of the vortex velocity profile produced by the applied current.
... One last issue that needs to be mentioned is the fact that above 20 T, the field gradients are so important that they create bubbles in the liquid helium [136], [137], [138] so the cooling process is less efficient and the sample is more likely to burn. This means that after one measurement above 20 T, the background field has to be set up again under 19 T to let the experiment cool down before the next current ramp. ...
Thesis
Recent improvements in High Temperature Superconductors (HTS) make them promising for large scale applications. They show astonishing properties, especially at very low temperature where they are able to carry high amount of current. These conductors are also built on a nickel alloy substrate allowing them to face severe mechanical stresses. For these reasons, HTS are now placed at the heart of numerous projects for building a next generation of high field magnets. This work is conducted in the NOUGAT project, which intends to design and build a 10 T HTS insert working in a 20 T background field. Despite their outstanding properties, HTS conductors show strong inhomogeneities in their performance along their length. This added to their high heat capacity can be at the origin of local hot spots. The transition to a dissipative state on this local area is then difficult to detect; because of the low speed of its propagation. The transition signal is likely to be lost in the high noise level environment, which can lead the winding to severe or irreversible damages.One way of dealing with this problem is to create coils where the electric insulation is removed and replaced by a metallic layer, the so-called Metal-as-Insulation winding technique. In this configuration and in a case of an inhomogeneity, the current bypasses through the turn-to-turn contact resistance and prevents the winding from burning. However, in such kind of winding field stability and linearity can be an issue. The slower dynamics obtained with this method prevent its use in some applications.The main focus of this work is therefore insulated coils especially the study of the transition behaviour to explore the possibility of reliable protections. In the same extend, the present work also considers safe ways to evaluate the performance of a wound sample in order for it to work with appropriate margins when at nominal operating conditions. This would decrease the need of a strong detection/protection system: the high heat capacity of the conductor makes windings unlikely to be damaged by an outside event.For practical reasons, the NOUGAT project will be built using MI technique, and therefore some MI coils results are presented in this work for comparison purpose. In a first step, the general design constrains for the NOUGAT project insert are defined, especially tape requirements and performance calculations. This underlines the necessity of characterizing the HTS conductor under high field and at low temperature, under conditions similar to the expected operation of the final insert prototype.In a second step, this experimental short sample characterization is implemented in a model to simulate the behaviour of pancake coils designed to build magnet. The aim of the model is to investigate on the transition start and propagation inside the winding. One of the main specificities is the simulation of the whole winding taking as an input the continuous critical current density measurement given by the providers at 77 K, self-field.The last axis of this work is the study of several wound samples allowing comparison between both insulated and metallic insulated windings. Their electric, magnetic, mechanic and thermal behaviours are examined as well as the coupling issues while working inside an outer magnet. Experimental results are compared to preliminary calculations and modelling results. An experimental protocol to safely evaluate coil performance margins is also proposed and tested successfully.Conclusions are then drawn about the possibility to operate safely full scale HTS magnets with present day conductor performances.
... This observation is further confirmed by the angular dependence of in-field critical current measurements shown in the inset of figure 7. A sharp J c /J sf c (θ) peak appears when the external magnetic field is parallel to the ab plane. This is attributed to both intrinsic pinning [18,19] and extrinsic planar defects parallel to the ab-planes such as stacking faults [20,21]. It is known that partial dislocations always form at the boundary between the stacking faults and REBCO matrix [22,23]. ...
Article
The development and application of second generation high temperature superconducting (2G-HTS) tapes have attracted much attention in China recently. Progress in upscaling high performance 2G-HTS tape production at Shanghai Superconductor Technology (SST) is reported in this paper. With ion beam assisted deposition, biaxially textured buffer layers with a configuration of CeO 2 /LaMnO 3 /MgO/Y 2 O 3 /Al 2 O 3 /C-276 have successfully been fabricated. In-plane and out-of-plane texture degrees of CeO 2 films achieve 2°-4° and 2°, respectively. A multi-plume multi-turn pulsed laser deposition (PLD) system combined with the so-called 'radiation assisted conductive heater' has been proposed and further developed for REBCO layer deposition. Our effort was focused on minimizing the temperature variations in the deposition region by modifying the heating shield that assists the conductive heater of the drum-like cylinder. A tape travelling speed of 100-180 m h ⁻¹ can be achieved with a steady temperature profile when passing through the deposition zone, which is very beneficial for the growth of the REBCO layer. Taking advantage of the liquid phase growth mode, several compositions of superconducting films with a thickness in the range of 1-2.5 μm have been grown with high growth rates of over 40 nm s ⁻¹ . Furthermore, the microstructures and superconducting performance were investigated in detail. Based on these studies, superconducting tapes with piece lengths of up to 500 meters have been developed. High I c values at 77 K, self-field (over 520 A cm ⁻¹ width) or at low temperature, high magnetic field conditions (over 560 A/4 mm width at 4.2 K, 10 T, perpendicular field) have been achieved. Lamination and jointing techniques have also been developed by SST for power and magnet applications.
... Критический ток ВТСП-2-провода в гелии в собственном магнитном поле в 10-15 раз выше его величины в азоте [8]. Во всех экспериментах, проведённых нами в гелии, ток всегда возрастал более чем десятикратно. ...
Article
Full-text available
ELECTROMECHANICAL PROPERTIES OF HTSC-2G WIRE WITH AISI 310S STAINLESS STEEL SUBSTRATE IN LIQUID HELIUM AND NITROGEN A.V. Krivykh, A. V. Polyakov NRC “Kurchatov Institute”, Moscow, Russia Now the possibility of creating a compact thermonuclear reactor with magnetic field 18-20 T is under consideration widely. It is obvious that only by the use of conductors based on HTSC-G2 materials such parameters can be provided. Estimates show that mechanical stresses in such systems can exceed 1000 MPa. Electromechanical tests of the first samples of HTSC-2G wires produced by NRC KI with a stainless steel substrate 310S at of liquid helium (4.2 K) and liquid nitrogen (77 K) temperatures has been carried out. Electrical and mechanical characteristics of the wire were measured simultaneously. The deformation of the samples was established by the readings of the extensometer. Wire stretching curves in liquid helium and nitrogen were obtained during electromechanical tests. The stress and strain values at which degradation of the current begins have been determined. The electrical voltage was measured in HTSC-2G wire with a critical current at levels of mechanical stresses 850 – 1100 MPa. Key words: electromechanical properties, HTSC-2G wire, liquid nitrogen (77 K), liquid helium (4,2 K), mechanical stresses
... This is due to the complicated relationship between anisotropic critical current and the specifics of the tape microstructure. For example, the ratio of critical current density values at 4.2 K, 19 T, B||c and at 77 K in the self-field, also known as "lift factor," may reach 10 in one kind of tapes, while other tapes yield a lift factor of only 2-3 [14]. Therefore, the critical current value should be estimated under field and temperature conditions close to the operating magnet conditions. ...
Article
Full-text available
The superconducting magnetic system (SMS) project is proposed. The second-generation high-temperature superconducting tapes for SMS are developed, fabricated and tested in NRC “Kurchatov Institute.” The magnet will be manufactured from non-insulated double pancake coils. Such a double pancake coil is manufactured and tested in liquid nitrogen. The integral radial resistance of this coil is determined.
... We conclude that TLAG-CSD is an ultrafast non-equilibrium and versatile process to grow epitaxial YBCO films at c axis growth rates of ∼ 100 nm s −1 from different routes. This is ~10-100 times faster than most of the thin film processes presently used 8,[29][30][31][32] to grow coated conductors and it confirms fast growth rates observed in other liquid-assisted techniques, such as in REBCO single crystal growth, REBCO bulk ceramic melt-textured growth 33 or REBCO films 14 . However here, the process is not restricted to the use of an equilibrium liquid phase and we demonstrate that the transient liquid formation is compatible with high-throughput CSD film manufacturing. ...
Article
Full-text available
The achievement of high growth rates in YBa2Cu3O7 epitaxial high-temperature superconducting films has become strategic to enable high-throughput manufacturing of long length coated conductors for energy and large magnet applications. We report on a transient liquid assisted growth process capable of achieving ultrafast growth rates (100 nm s−1) and high critical current densities (5 MA cm−2 at 77 K). This is based on the kinetic preference of Ba-Cu-O to form transient liquids prior to crystalline thermodynamic equilibrium phases, and as such is a non-equilibrium approach. The transient liquid-assisted growth process is combined with chemical solution deposition, proposing a scalable method for superconducting tapes manufacturing. Additionally, using colloidal solutions, the growth process is extended towards fabrication of nanocomposite films for enhanced superconducting properties at high magnetic fields. Fast acquisition in situ synchrotron X-ray diffraction and high resolution scanning transmission electron microscopy (STEM) become crucial measurements in disentangling key aspects of the growth process. High throughput manufacturing of long length coated conductors requires fast epitaxial growth of high-temperature superconducting films. Here, Soler et al. report an ultrafast growth rates and high critical current densities of YBa2Cu3O7 films using a transient liquid-assisted growth method.
Article
In order to further understand the multiplume and multiturn PLD process, we propose a strategy to diagnose the issues of 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> films deposited in a reel-to-reel manner. Especially, the test tapes after passing through each turn were deposited. Optical microscopy observation on the test tapes reveals that the void defects on the REBCO films are probably related to grain boundaries of the CeO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> cap layer, and such defects become dense and randomly distributed after more turns deposition. XRD analysis indicates that the test tapes deposited at all the turns exhibit strong c-axis orientation. With increasing the number of turns (i.e., increase the film thickness) by passing more times of deposition zone, enhancement of the crystallinity in the REBCO films is found. However, for the tape deposited at the last turn, both the structure characterization and Ic value suggest that the deposition conditions are out of the temperature window margin for growth of the high-performance REBCO film. The advantage of this method is to obtain superconducting film deposited at each turn without changing the deposition conditions, and the issues of superconducting films deposited at each turn can be easily diagnosed.
Article
Second-generation high-temperature superconductors (HTS) REBCO are promising for high-field application due to the excellent $j_{c}(B)$ performance at low temperatures and for power transmission at liquid nitrogen temperature. For power transmission with HTS, the formation of high-current HTS cables from single HTS tapes is desirable for cable currents of several 10 kA up to more than 100 kA. On the other hand, to avoid high inductances, which would cause high-voltage problems in case of quench or fast shutdown, high-current HTS cables are needed for larger high-field magnets, too, typically operated at 4.5 K or lower. In the last years, several HTS cable designs have been proposed, such as twisted stacked cable, CORC cable, and Roebel cable. This talk will give an overview of such proposals and highlight actual developments in HTS cable design and REBCO tape optimization, e.g., for highest field. In addition, an optimization of round TSTC strand will be introduced, which is designed for simple fabrication in long lengths for versatile use either for the production of cables to be used at high fields or for power transmission.
Article
Pulsed laser deposition (PLD) is classically considered as a very reliable process that provides correct stoichiometry of the deposited layer when the deposition speed is below 0.1 nm per deposition pulse. Initially, we found significant critical currents of 200-400 A/cm-width by very high deposition rates. Later, in this work, a study of reproducibility and feasibility of high- and ultrahigh-speed PLD is performed. With high speed, we denote a range from 0.1 to 0.3 nm/pulse, whereas ultrahigh speed corresponds to higher numbers, i.e., above 0.3 nm/pulse. At ultrahigh laser energy density, an optimum deposition rate is found that maximizes the critical current, i.e., Ic. The Ic at this maximum may reach 500-700 A/cm-width by relatively low (< 1.5 MA/cm2) Jc. The optimal deposition rate and energy density may be employed in cost-feasible technological solutions because deposition time may be shortened by a factor of ∼5. A suggested double-layer model with different critical currents in layers provides good fitting of the experimental dependence.
Article
Progress in the upscaling of multibeam pulsed laser deposition (PLD) is reported. Tapes 220 m long were repeatedly processed using an extended drum in PLD installation employed for the deposition of ceria cap buffer and YBCO layers. A Cr-Ni stainless steel tape preliminary coated with a biaxially textured yttria-stabilized-zirconia buffer layer via alternating-beam-assisted deposition was used as a substrate. In 2014, the upscaling of the PLD technique was performed in three steps. In the first step, a 22-m-long tape with record "in-field" critical current (500 A in a 4-mm-wide tape at 4.2 K, 18 T, B//c) was achieved in February 2014. The second step enabled the deposition of 110-130-m-long tapes with moderate (20%) reduction of critical current and sufficiently small local dropouts of the current. The third step resulted in the upscaling of tape processing to 230 m in length. First tapes of such length were already obtained in December 2014. Further upscale of the tape length toward 600 m and more is in progress so far. The most important feature of the PLD process is that the critical current in the coated conductors demonstrates no reduction in the end of the tape, which was exposed to a single run of translation of the rotating drum with the tape, i.e., from one end to the other end. Moreover, in many cases, a tendency of increase of critical current was observed during deposition run. Pulses of oxygen pressure formed by the deposition system together with the influence of barium zirconate precipitations enabled rather high in-field critical currents in 230-m-long tapes.
Article
In this work, we present a study of the resistive transition in magnetic field of 2G high-temperature superconductor wire samples with BaSnO3 (BSO) artificial pinning centres (APCs) in a GdBa2Cu3O7−x (GdBCO) superconductor. The GdBCO layer was fabricated by pulsed laser deposition, using production equipment to obtain samples with varied concentrations of APC: 0, 6, 12 and 18 mol% of BSO. Resistive transition curves were measured in the magnetic field range from 0 to 9 T, and magnetic field orientations from Bmidmidc (θ = 0°) to Bmidmidab (θ = 90°) with an angle step of 15°. We observed an irreversibility temperature peak at the Bmidmidab orientation. We determined the angular regions where correlated pinning centres dominated and found them to expand with the increase of BSO concentration. The activation energy (U a) obtained from the lg(ρ/ρ 0) against the 1/T plots was almost constant in the whole angular range, with a small peak at Bmidmidab. The activation energy as well as the irreversibility temperature decreased with the increasing doping level, but the U a(θ) curves looked similar for all samples with APCs. The logarithmic resistivity plot of the undoped sample looked substantially different from those of the APC samples, with a kink and two different slopes corresponding to two regions with different U a. We discuss that this difference is related to the different pinning landscapes in samples with and without APCs.
Article
The influence of magnetic flux creep on the dynamics of vortices in percolation superconductors containing fractal clusters of the normal phase has been considered. Dependences of the resistance of these superconductors on the transport current are obtained for different fractal dimensions of cluster boundaries. It is established that the vortex-glass state is implemented in percolation superconductors with a fractal cluster structure under collective creep of vortices.
Article
Full-text available
The in-field orientation dependence of critical current and n-value in second generation high temperature superconductive tapes was investigated. The samples were manufactured by Metalorganic Chemical Vapour Deposition method with BaZrO3 inclusions (SuperPower Inc.) and Pulsed Laser Deposition method (Bruker HTS). For samples of each kind of fabrication techniques we observed higher critical current value in the case of external magnetic field aligned along (or nearby) c-axis direction in comparison with one aligned along ab-plane. We analysed possible reasons for this effect. Angular dependences of the critical current and n-value were investigated. The microstructure images of superconductive layer of studied samples show tilt of BaZrO3 nanorods in MOCVD sample and high density of structural defects for PLD sample.
Article
The current carrying capabilities of high critical temperature (T <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</sub> ) technical conductors have considerably improved in recent years, and this has practical consequences on the requirements of the measurement equipment. We have designed, constructed, and tested a probe for high-current, high-precision critical current measurements in liquid helium and in gas flow at different temperatures. To minimize the ohmic heating and the thermal conduction losses, the probe employs high-temperature superconductors (HTS) current leads rated at 2000 A, which are cooled by the exhaust helium gas at temperatures below 70 K. An active temperature stabilization system keeps the sample temperature constant at the target during current runs with a precision of ±0.01 K. It consists of a proportional-integral-differential loop that controls heaters close to the sample taking the current-induced heating effects into account. We present the design of the probe and data collected on HTS from different manufacturers, which highlight the performance of the system.
Article
The influence of fractal normal phase clusters on the electric field induced by the flow and creep of the magnetic flux in percolation superconductors has been considered. The current–voltage characteristics of such superconductors with allowance for the influence of the fractal dimension of cluster boundaries and the pinning barrier height have been obtained. The vortex dynamics in percolation superconductors with a fractal cluster structure in a viscous flow of the magnetic flux, the Anderson–Kim creep, and the collective flux creep has been analyzed. It has been discovered that the fractality of normal phase clusters reduces the electric field arising in the initial stage of the resistive transition.
Article
Superconducting magnets with magnetic fields of approximately 20 T will be needed for future high-energy accelerators, such as the Future Circular Collider at CERN and/or the Muon Collider in the United States. Such field strengths exceed the levels achievable using low-temperature superconductors, such as Nb3Sn or Nb3Al. Only hightemperature superconductors can currently achieve such high field strengths. However, there has been little research published on the electrical transport properties of REBCO coated conductors in high-field, low-temperature magnet applications. Thus, we have started the critical current characterization of commercially available REBCO-coated conductors in fields of up to 18 T at 4.2 K. This paper reports some of the critical current measurement results at 4.2 K and 77 K for conductors from four different manufacturers: Fujikura Ltd.; SuNAM Co., Ltd.; SuperOx Japan LLC; and SuperPower Inc.
Article
Alternative concepts based on (i) drum design and (ii) reel-to-reel design were studied in the course of the development of industrial technology of long (up to 600 m) YBCO coated tapes. According to our previous route we investigated double disordered YBCO layers deposited by using extrinsic precipitations as well as intrinsic precipitations and structural defects. These superimposing of the nano-defect and inhomogeneities resulted in very high critical currents optimized for high-field operation. The HTS layers in our experiments were deposited onto CrNi stainless steel substrates which were polished and buffered with an in-plane textured yttria-stabilizedzirconia layer, 1.2-2 μm thick. Critical currents in 220 m and 550 m long tapes were 20-30 % lower compared to length of 20 m, but still representing champion current values for long tapes. Development of the process based on drum concept resulted in finding a relationship between the tape throughput and the a wall thickness of the drum. A concept of light, dynamic drum with thin walls, reduced heat capacity and radial elasticity was analyzed and employed in processing of long, up to 600 m YBCO coated tapes. Comparison between drum and reel-to-reel techniques is provided. Newest status in long tape processing is reported.
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To increase the throughput and to further improve the performance of REBCO superconductors are two hot topics for deposition of REBCO by pulsed laser deposition (PLD) routes. In this work, we developed a radiation assisted conductive heating (RACH) technique, in order to obtain homogeneous temperature on the tape surface when passing the deposition zone at dynamic PLD process. Three series of high performance REBCO productions: material A, B and C have been fabricated for power and magnet applications. High $J_c$ of 3 MA/cm2 at 77 K self-field was achieved at film thickness over 2 μm and excellent $I_c$ homogeneity along the length was achieved for over 300 meters long tape. Compared with traditional conductive heating mode, in-field $I_c$ performances were increased by over 50% at 30 K and 4.2 K on the REBCO tape with optimized composition by using the RACH PLD system. Moreover, high tape travelling speed of over 100 m/h was used for all the REBCO deposition process, which provides possibility of up-scaling the techniques for meeting requirements of the mass production. Improvements of superconductivity performance demonstrates that the RACH technique is a high-efficient and stable approach for long-length REBCO tape fabrication.
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Our project is to build an HTS insert generating 10 T in its center and expected to work inside a 20 T background field. In a first step, the background field is provided by a resistive magnet to avoid major coupling issues. Nevertheless, the final goal is to have the insert operating inside a LTS magnet to yield a 30 T-class all-superconducting magnet. The insert is designed as a stack of pancakes and double pancakes wound with REBCO tapes. Preliminary tests are performed on a deposited polyimide insulated coil, although design has started with metallic-insulation coils. This paper presents results obtained on a double pancake insulated HTS coil that was tested inside both a resistive coil at LNCMI and a superconducting magnet at Tohoku University. The electrical and mechanical behaviors of the sample coil are discussed, and margins are estimated taking into account the field distribution on each point of the coil. Results are encouraging as the coil passes 370 A (82.9 % lc) self-field and 260 A (68.6 % lc) under 8 T. Moreover, the coil is still working even after the outer magnet quench.
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In this work, polycrystalline samples of nominal composition YBa2Cu3O7−δ with co-addition of 5.0 mol% of Y2O3 and x mol% of BaZrO3 (BZO) nanoparticles (x = 0.0, 1.0, 2.0, 3.0, 5.0 and 7.0) were prepared using co-precipitation (COP) method. Data of X-ray diffraction (XRD) showed that all the samples were composed of Y-123 as the major phase and Y-211 as the minor phase. XRD peak of BZO was also observed in the samples co-added with BZO nanoparticles. Refinement of lattice parameters of a, b, and c-axis showed that the orthorhombic structure of the samples was retained without occurance of orthorhombic-tetragonal phase transition. The average grain size was increased from 0.30 ± 0.02 µm for the pure sample to 0.47 ± 0.03 µm for the sample with 7.0 mol% BZO as revealed by the scanning electron microscope images. Plots of normalized resistance versus temperature showed metallic behavior in the normal state and a single step transition in the samples. Tc-onset was decreased with co-addition of Y2O3 and BZO probably because of reduced hole concentration. The higher Josephson’s current, Io of the samples with co-addition of 0.0–2.0 mol% BZO compared with that of the pure one is likely to be due to improved grain coupling as shown by the AC susceptibility measurement. The calculated intergranular critical current density, Jcm based on the Bean critical state model is 1.88 A/cm² at Tp = 84.8 K for the pure sample. The highest Jcm obtained is 2.10 A/cm² at Tp = 85.4 K for 2.0 mol% BZO co-added sample.
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Understanding the critical current performance variation of Nb3Sn superconducting wires under mechanical loading is a crucial issue for the design of next generation accelerator and fusion magnets. In these applications, the mechanical properties of the conductors may become a limiting factor due to the strong electro-magnetic forces resulting from the combination of large magnets and intense magnetic fields. In particular, the presence of voids in the superconducting filament structure, which are formed during the fabrication and the reaction heat treatment, determines localized stress concentrations and possibly the formation of cracks. In this work, we demonstrate a quantitative correlation between the void morphology and the electro-mechanical limits measured on different Bronze route Nb3Sn wires. Hot Isostatic Pressing (HIP) prior to the reaction heat treatment is utilized to partially eliminate the voids. The wires' void distributions - with and without HIP treatment - are detected and statistically analyzed using high energy X-ray micro tomography. The stress concentration due to the shape and distribution of the voids as well as their impact on the electro-mechanical properties are determined through finite element method modeling. Finally, the results are quantitatively correlated with the experimentally determined limits of the irreversible critical current degradation upon mechanical loading.
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Scaling relations describing the electromagnetic behaviour of coated conductors (CCs) greatly simplify the design of REBCO-based devices. The performance of REBCO CCs is strongly influenced by fabrication route, conductor architecture and materials, and these parameters vary from one manufacturer to the others. In the present work we have examined the critical surface for the current density, Jc(T,B,$\theta$), of coated conductors from six different manufacturers: American Superconductor Co. (US), Bruker HTS GmbH (Germany), Fujikura Ltd. (Japan), SuNAM Co. Ltd. (Korea), SuperOx ZAO (Russia) and SuperPower Inc. (US). Electrical transport and magnetic measurements were performed at temperatures between 4.2 K and 77 K and in magnetic field up to 19 T. Experiments were conducted at three different orientations of the field with respect to the crystallographic c-axis of the REBCO layer, $\theta$ = 0$\deg$, 45$\deg$ and 90$\deg$, in order to probe the angular anisotropy of Jc. In spite of the large variability of CCs performance, we show here that field and temperature dependences of Jc at a given angle can be reproduced over wide ranges using a scaling relation based only on three parameters. Furthermore, we present and validate a new approach combining magnetic and transport measurements for the determination of the scaling parameters with minimal experimental effort.
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REBa2 Cu 3Ox ((REBCO), RE = rare earth) superconductor tapes with moderate levels of dopants have been optimized for high critical current density in low magnetic fields at 77 K, but they do not exhibit exemplary performance in conditions of interest for practical applications, i.e., temperatures less than 50 K and fields of 2–30 T. Heavy doping of REBCO tapes has been avoided by researchers thus far due to deterioration in properties. Here, we report achievement of critical current densities (Jc) above 20 MA/cm2 at 30 K, 3 T in heavily doped (25 mol. % Zr-added) (Gd,Y)Ba2 Cu 3Ox superconductor tapes, which is more than three times higher than the Jc typically obtained in moderately doped tapes. Pinning force levels above 1000 GN/m3 have also been attained at 20 K. A composition map of lift factor in Jc (ratio of Jc at 30 K, 3 T to the Jc at 77 K, 0 T) has been developed which reveals the optimum film composition to obtain lift factors above six, which is thrice the typical value. A highly c-axis aligned BaZrO3 (BZO) nanocolumn defect density of nearly 7 × 1011 cm−2 as well as 2–3 nm sized particles rich in Cu and Zr have been found in the high Jc films.
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In pulsed laser deposited YBa2Cu3O7−x thin films containing 5 mol. % Ba2YNbO6 pinning additions, we show that a growth rate of 1 nm/s (10 Hz laser repetition rate with an instant rate ∼0.1 nm/pulse) gives remarkably strong c-axis correlated pinning which is associated with the presence of Ba2YNbO6 nanocolumns. This is different to the behaviour of other well-studied pinning additions where only random nanoparticles of the pinning phase are present at high growth rates and is an important finding for industrial fabrication of coated conductors where fast growth is required.
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Applications of REBCO coated conductors are now being developed for a very wide range of temperatures and magnetic fields and it is not yet clear whether vortex pinning strategies aimed for high temperature, low field operation are equally valid at lower temperatures and higher fields. A detailed characterization of the superconducting properties of a 15 mol. % Zr-added REBCO thin film made by metal organic chemical vapor deposition, from 4.2 to 77 K under magnetic fields up to 31 T is presented in this article. Even at a such high level of Zr addition, Tc depression has been avoided (Tc = 91 K), while at the same time an exceptionally high irreversibility field Hirr ≈ 14.8 T at 77 K and a remarkably high vortex pinning force density Fp ≈ 1.7 TN/m3 at 4.2 K have been achieved. We ascribe the excellent pinning performance at high temperatures to the high density (equivalent vortex matching field ̃7 T) of self-assembled BZO nanorods, while the low temperature pinning force is enhanced by large additional pinning which we ascribe to strain-induced point defects induced in the REBCO matrix by the BZO nanorods. Our results suggest even more room for further performance enhancement of commercial REBCO coated conductors and point the way to REBCO coil applications at liquid nitrogen temperatures since the critical current density Jc(H//c) characteristic at 77 K are now almost identical to those of fully optimized Nb-Ti at 4 K.
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REBa2Cu3Oy, (RE : rare earth elements, RE123) coated conductors are expected to show high performance in superconducting applications, due to their high mechanical strength and high current density in magnetic fields. Fujikura has developed ion-beam-assisted-deposition (IBAD) and pulsed-laser-deposition (PLD) technique, and today we routinely manufacture coated conductors with length over 500 m and Ic over 500 A/cm-width at 77 K, self field. We have also been able to fabricate long conductors with higher Ic by thickening RE123 layer. Although Ic performances at 77 K, self field are important, but performances in magnetic fields at lower temperatures below 77 K are more important for coil applications. In this work, we evaluated coated conductors with thick RE123 layer in magnetic fields at low temperatures. All samples are fabricated with long length. We measured samples by four-probe transport method at wide temperature range from 77 K to 10 K by using cryo-cooled cryostat. A conductor with 5.5 μm thick RE123 exhibits high Ic values of 937 A/cm-width at 77 K, self field, 637 A/cm-width at 50 K, 5T and 976 A/cm-width at 40 K, 5T.
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A new model of light-target interaction, which takes into account multiple interaction of the scattered laser beam with the surface structure of a target, is reported. The model is based on calculations of the local intensity of the electromagnetic wave, from which the local amount of ablated material can be obtained after each simulated laser pulse. The simulations of the sequence of laser pulses was employed to explain the observed development of the particular surface topography. It is shown that during laser ablation a small initial surface roughness is sufficient to initiate further deepening of the surface relief. During this preliminary development of the relief, the 1st-order scattering plays a dominant role. But, as soon as the surface acquired a relatively deep relief, the 2nd-order interaction leads to the appearance of "hot" valleys, where the electromagnetic energy of the light wave is significantly more concentrated and, therefore, the ablation is more efficient. As a result of this effect the depth of the valleys increases and the cone structure becomes more and more pronounced.
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High-temperature superconductors of the second generation—coated conductors—are based on an architecture of YBCO films deposited on a well-textured substrate tape. The deposition technique used in the processing of YBCO films is responsible not only for both the resulting critical currents in the conductors and the cost efficiency of the employed production route, but also for the ultimate viability of the chosen technology. This article describes an advanced deposition method for YBCO films using high-rate pulsed laser deposition (HR-PLD).An elaborate variable azimuth ablation allows target roughening to be considerably reduced in the course of continuous deposition, and as a result, the integral deposition speed and speed stability can be increased to technologically interesting high values.Well-selected process parameters have been demonstrated to yield high currents of up to 480A/cm-width in short tapes and 360A/cm-width in 6-m-long tapes.Together with quasi-equilibrium heating, the HR-PLD method allows the processing of long-length YBCO-coated conductors and offers a cost-efficient route for their production on an industrial scale.
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The traditional view of the surface diffusion of metal atoms on metal surfaces was that atoms carry on a random walk between nearest-neighbor surface sites. Through field ion microscopic observations and molecular dynamics simulations this picture has been changed completely. Diffusion by an adatom exchanging with an atom of the substrate has been identified on fcc(110), and subsequently also on fcc(100) planes. At elevated temperatures, multiple events have been found by simulations in which an atom enters the lattice, and a lattice atom at some distance from the entry point pops out. Much at the same time the contribution of long jumps, spanning more than a nearest-neighbour distance, has been examined; their rates have been measured, and such transitions have been found to contribute significantly, at least on tungsten surfaces. As higher diffusion temperatures become accessible, additional jump processes can be expected to be revealed.
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High quality high-temperature-superconducting YBa2Cu 3O7-x (YBCO) films for industrial applications demand very high critical current densities Jc, which can only be achieved by strong three-dimensional (3D) pinning with deliberately introduced nano-precipitates. The purpose of this thesis is to provide an in-depth understanding of the 3D pinning in such YBCO films. In pulsed laser deposition (PLD) prepared YBCO films, a high density of anti-phase boundaries and stacking faults were found to be effective pinning defects for improving Jc in small fields. However, their failure to improve Jc at high fields shows that such naturally generated defects are not strong 3D pinning centers. A demonstration of strong 3D pinning was found in a metal organic chemical vapor deposition (MOCVD) grown YBCO coated conductor (CC) with a high density of (Y,Sm)2O3 nano-precipitates. We observed a significantly enhanced irreversibility field Hirr which, like other superconducting properties was independent of thickness, due to strong vortex-pin interactions. The advantage of 3D pinning was further illustrated by a bi-layer metalorganic deposition (MOD) grown YBCO CC with different 3D pinning structures in each layer. The Jc anisotropy of the bilayer was found to be the thickness-weighted sum of the anisotropy of the two individual layers, demonstrating an applicable way to tune the Jcanisotropy. Moreover, extensive low temperature and high magnetic field evaluations performed on an MOCVD CC with dense 3D (Y,Sm) 2O3 nano-precipitate pinning centers showed that its strong vortex pinning at 77 K correlated well to strong performance at 4.2 K too. YBCO films with quantitatively controlled artificial Y2O 3 nano-precipitates were also grown by PLD, and characterized over wide temperature and field ranges. Their Jc was found to be determined by the vortex pinning mediated by thermal fluctuation effects. In weak thermal-fluctuation situations Jc increased with decreasing effective precipitate spacing Lc. In other situations, Jc depends on both Lc and the size and elementary pinning strength of the nano-precipitates. In summary, this thesis presents detailed pinning studies on several differently grown YBCO films. Our results identify the optimum pinning structures in YBCO films and provide a systematic guidance for optimizing vortex pinning.
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We have fabricated YBa2Cu3O7−x (YBCO) multi-layer films by pulsed laser deposition (PLD) method on a metallic substrate. The multi-layer structure was composed of YBCO and YBCO with the bamboo structure, which is the columnar microstructure of YBCO/BaZrO3 (BZO) and is effective for pinning. From the transmission electron microscopy (TEM), the bamboo structure was well-established on the YBCO layer. In a magnetic field angular dependence of Ic, it seemed that the anisotropy was improved in the multi-layer film. It was considered that the insertion of the YBCO layer into the bamboo layer contributes to random pinning for the magnetic field vertical to the c-axis, and then the anisotropy was improved.
In standard ion beam assisted deposition (IBAD), the growing film is exposed to inclined ion etching in order to achieve a preferable in-plane orientation of the crystalline structure. Recently, we suggested exposing the film periodically to deposition pulses and to etching pulses, i.e. to assisted beam pulses. As a long sequence of alternations of these two pulses is needed, we named this method “alternating beam assisted deposition” (ABAD). In real application, the substrates exposed to the molecular/atomic flow originating from the sputter source acquire a few nanometer thick layer of yttria-stabilized zirconia (YSZ). In the next step, this layer undergoes ion etching with an Ar ion beam emitted from the source with a particle energy between 200 and 300 eV. Simultaneously with ion-beam exposition, an additional electron beam provides neutralizing of the electrical change in the substrate plane. The ion beam guided 55° at a 55° angle of incidence provides selective etching of the YSZ layer, leading finally after numerous deposition-etching cycles to a sufficiently high quality of in-plane texture in the YSZ layer with the best FWHM values of 8°-9°.
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A new development of the pulsed laser ablation (PLA) technique based on variable azimuth ablation (VAA) is reported. The VAA itself is based on periodic variations of the azimuth of the laser beam relative to the target at a constant angle of beam incidence. Such variations result in a suppression of cone-valley surface structures which tend to develop in the case of a fixed azimuth. VAA leads to high-level stabilization of the laser plume during a long-term deposition process. As a result, the VAA method stabilizes the deposition rate with a tolerance of only 3-6% instead of a 90% decrease in the rate as in conventional PLA. Different possibilities for the realization of the VAA technique based on 2- and 3-way target scans are discussed. In the case of large areas, VAA technique with a meander beam target scan is capable of the deposition of high-quality multicompositional superconducting films on tubes and tapes more than 1 m in length.
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Second-generation (2G) HTS wires are now being produced routinely in kilometer lengths using Metal Organic Chemical Vapor Deposition (MOCVD) process with critical currents of 300 A/cm. While this achievement is enabling several prototype devices, in order to reach a substantial commercial market, the cost-performance metrics of 2G HTS wires need to be significantly improved in device operating conditions. Zr-doping has been found to be an effective approach to improve in-field critical current performance of MOCVD-based HTS wires. In this work, we have explored modifications to the Zr-doped precursor compositions to achieve three and two-fold increase in deposition rate in research and production MOCVD systems respectively. Production wires made with modified Zr-doped compositions exhibit a self-field critical current density of 50 MA/cm<sup>2</sup> at 4.2 K and a 55 to 65% higher performance than our previous wires with Zr-doping, over magnetic field range of 0 to 30 T. We have also developed an alternate, low-cost technique, namely electrodeposition, to deposit silver overlayer on superconducting film. Wires made with electrodeposited silver are able to sustain the same level of overcurrent as sputtered silver layers. This process has been successfully scaled up to 100 m lengths.
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By applying high-rate copper electroplating technique the reliable fabrication of a copper stabilizer on coated conductor with an 1 μm Ag cap is investigated. The obtained mechanical, electrical and encapsulation properties due to a 20 μm thick Cu stabilizer on the surface improve the practical and technical performance. A copper sulphate CuSO<sub>4</sub> based pulse plating technique is capable to deposit a 20 micrometer thick copper layer in a fast and continuous non-vacuum process. A surround Cu layer protects the HTS conductor surface against salt aqueous solutions, humidity, and against cryogenic liquids LN<sub>2</sub> and liquid helium. With the copper stabilizer conductor solder joining with a contact resistance of 200 nΩcm<sup>2</sup> becomes possible. Further effort is being made to develop and construct a high-rate and high throughput continuous reel-to-reel modular plating unit for deposition of long length ( >; 400 m). The paper describes the practical achievements within the conductor fabrication.