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ABSTRACT: REBa2Cu3Ox (REBCO) films can achieve remarkably high critical current density Jc values by the incorporation of insulating nanoparticles. A particularly interesting case concerns BaZrO3 (BZO) nanorods which strongly enhance Jc at high temperatures and fields up to a few tesla. Here we investigate the full angular transport Jc over a much broader range of field (up to 31 T) and temperature (4.2–77 K), a range suitable for new very high field magnet applications. We show that the correlated c-axis pinning of BZO nanorods becomes progressively less obvious at lower temperatures and indeed at 4.2 K up to 31 T, the only visible correlated pinning is for fields parallel to the film plane. Jc at 4.2 K is still, however, strongly enhanced by the BZO nanorods, as is clearly manifested by a remarkably high bulk pinning force density Fp ≈ 900 GN/m3 for H‖c, because the BZO nanorods add weak but very dense pins which contribute up to half of Jc in the low temperature limit. Above about 30 K these dense but weak pins lose their effectiveness and Jc then becomes dominated by the sparse but strong BZO pins. This strong temperature dependence of the dominant pinning effects of multiple pin types makes broad range characterization essential to reveal the great flexibility of pinning in modern REBCO films that is almost certainly not yet fully optimized.
Phys. Rev. B. 09/2012; 86(11).
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ABSTRACT: REBa$_{2}$Cu$_{3}$O$_{x}$ films can achieve remarkably high critical current
density values by the incorporation of insulating nanoparticles. A particular
interesting case concerns BaZrO$_{3}$ (BZO) nanorods, whose strongly correlated
effect is seen at high temperatures. Here we investigate the field, temperature
and angular dependence of the critical current density over a wide temperature
range from 4.2 K to 77 K, and magnetic fields up to 31 T. We show that the
correlated c-axis pinning of BZO nanorods becomes progressively less obvious at
lower temperature. Indeed at 4.2 K and fields up to 31 T, the only correlated
pinning is for fields parallel to the film plane. We interpret the change as
being due to significant contributions from dense but weak pins that thermal
fluctuations render ineffective at high temperatures but which become strong at
lower temperatures.
11/2011;
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V. Selvamanickam,
Y. Chen,
I. Kesgin,
A. Guevara,
T. Shi,
Y. Yao,
Y. Qiao,
Y. Zhang,
G. Majkic,
G. Carota,
A. Rar,
Y. Xie,
J. Dackow,
B. Maiorov,
L. Civale,
V. Braccini,
J. Jaroszynski, A. Xu,
D. Larbalestier,
R. Bhattacharya
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ABSTRACT: 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.
IEEE Transactions on Appiled Superconductivity 07/2011; · 1.04 Impact Factor
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V. Braccini, A Xu,
J. Jaroszynski,
Y Xin,
D. C. Larbalestier,
Y Chen,
G. Carota,
J Dackow,
I Kesgin,
Y Yao,
A Guevara,
T Shi,
V. Selvamanickam
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ABSTRACT: BaZrO3 (BZO) nanorods are now incorporated into production IBAD-MOCVD coated conductors. Here we compare several examples of both BZO-free and BZO-containing coated conductors using critical current (Ic) characterizations at 4.2 K over their full angular range up to fields of 31 T. We find that BZO nanorods do not produce any c-axis distortion of the critical current density Jc(theta) curve at 4.2 K at any field, but also that pinning is nevertheless strongly enhanced compared to the non-BZO conductors. We also find that the tendency of the ab-plane Jc(theta) peak to become cusp-like is moderated by BZO and we define a new figure of merit that may be helpful for magnet design - the OADI (Off-Axis Double Ic), which clearly shows that BZO broadens the ab-plane peak and thus raises Jc 5-30{\deg} away from the tape plane, where the most critical approach to Ic occurs in many coil designs. We describe some experimental procedures that may make critical current Ic tests of these very high current tapes more tractable at 4.2 K, where Ic exceeds 1000 A even for 4 mm wide tape with only 1 micron thickness of superconductor. A positive conclusion is that BZO is very beneficial for the Jc characteristics at 4.2 K, just as it is at higher temperatures, where the correlated c-axis pinning effects of the nanorods are much more obvious.
11/2010;
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H.W. Weijers,
U.P. Trociewitz,
W.D. Markiewicz,
J. Jiang,
D. Myers,
E.E. Hellstrom, A. Xu,
J. Jaroszynski,
P. Noyes,
Y. Viouchkov,
D.C. Larbalestier
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ABSTRACT: Development of high-field magnets using high temperature superconductors (HTS) is a core activity at the NHMFL. Magnet technology based on both YBCO-coated tape conductors and Bi-2212 round wires is being pursued. Two specific projects are underway. The first is a user magnet with a 17 T YBCO coil set which, inside an LTS outsert, will generate a combined field of 32 T. The second is a 7 T Bi2212 demonstration coil set to be operated in a large bore resistive magnet to generate a combined magnetic field of 25 T. Owing to the substantial technological differences of the two conductor types, each project faces different conductor and magnet technology challenges. Two small coils have been tested in a 38-mm cold bore cryostat inserted in a 31 T resistive magnet: a Bi2212 round-wire layer-wound insert coil that generated 1.1 T for a total of 32.1 T and a YBCO double-pancake insert that generated 2.8 T for a total central field of 33.8 T. Four larger layer-wound coils have been manufactured and tested in a 20 T, 186-mm cold bore resistive magnet: a sizeable Bi-2212 coil and three thin large-diameter YBCO coils. The test results are discussed. The current densities and stress levels that these coils tolerate underpin our conviction that >30 T all-superconducting magnets are viable.
IEEE Transactions on Appiled Superconductivity 07/2010; · 1.04 Impact Factor
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ABSTRACT: A small coil was made and tested for the purpose of magnet technology development for YBa2Cu3O7−x (YBCO) high field coils. The coil has a winding inner diameter of 24 mm, outer diameter of 36 mm, and length of 46 mm in a pancake wound construction of 5 double pancakes. The YBCO conductor is SuperPower SCS4050 with 2×20 μm of copper stabilizer. The coil was tested in the high field user facility of the NHMFL in a 31 T background field magnet. At this background field, the coil was operated to a current of 325 A and produced a field increment of 2.8 T for a record total field of 33.8 T. The average current density in the windings at full current was very high at 446 A/mm2. The test was complicated by the accumulation of trapped helium gas about the coil due to the diamagnetic effect of helium at high field. Even though the coil operated at elevated temperature during the high field test, the coil performance was limited by mechanical degradation and not a critical current limit.
AIP Conference Proceedings. 04/2010; 1218(1):225-230.
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ABSTRACT: We present very high field angle dependent critical current density (Jc) data for three recently obtained YBa2Cu3O7−x (YBCO) coated conductors used in the construction of high field solenoids. We find that strongly correlated pins, such as BaZrO3 (BZO) nanorods, while yielding strong c-axis peaks at 77 K, produce almost no measurable contribution at 4 K. Raising the field from <5 to 30 T at 4 K causes a marked transition from a Ginzburg–Landau-like Jc(θ) at low fields to a marked cusp-like behavior at high fields. Transmission electron micrographs show that all samples contain a high density of stacking faults which strengthen the plane correlated pinning parallel to the ab planes produced by the intrinsic ab-plane pinning of the Cu–O charge reservoir layers.
Superconductor Science and Technology 12/2009; 23(1):014003. · 2.66 Impact Factor
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S Lee,
J Jiang,
J. D. Weiss,
C M Folkman,
C. W. Bark,
C. Tarantini, A Xu,
D. Abraimov,
A. Polyanskii,
C T Nelson,
Y Zhang,
S H Baek,
H W Jang,
A Yamamoto,
F Kametani,
X. Q. Pan,
E. E. Hellstrom,
A. Gurevich,
C. B. Eom,
D. C. Larbalestier
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ABSTRACT: We show that despite the low anisotropy, strong vortex pinning and high irreversibility field Hirr close to the upper critical field Hc2 of Ba(Fe1-xCox)2As2, the critical current density Jgb across [001] tilt grain boundaries (GBs) of thin film Ba(Fe1-xCox)2As2 bicrystals is strongly depressed, similar to high-Tc cuprates. Our results suggest that weak-linked GBs are characteristic of both cuprates and pnictides because of competing orders, low carrier density, and unconventional pairing symmetry. Comment: To appear in Applied Physics Letters
07/2009;
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S. Lee,
J. Jiang,
J. D. Weiss,
C. M. Folkman,
C. W. Bark,
C. Tarantini, A. Xu,
D. Abraimov,
A. Polyanskii,
C. T. Nelson,
Y. Zhang,
S. H. Baek,
H. W. Jang,
A. Yamamoto,
F. Kametani,
X. Q. Pan,
E. E. Hellstrom,
A. Gurevich,
C. B. Eom,
and D. C. Larbalestier
Applied Physics Letters 01/2009; 95(212505). · 3.84 Impact Factor
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S Lee,
J Jiang,
J D Weiss,
C M Folkman,
C W Bark,
C Tarantini, A Xu,
D Abraimov,
A Polyanskii,
C T Nelson,
Y Zhang,
S H Baek,
H W Jang,
A Yamamoto,
F Kametani,
X Q Pan,
E E Hellstrom,
A Gurevich,
C B Eom,
D C Larbalestier
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ABSTRACT: We show that despite the low anisotropy, strong vortex pinning and high irreversibility field H irr close to the upper critical field H c2 of Ba(Fe 1-x Co x) 2 As 2 , the critical current density J gb across [001] tilt grain boundaries (GBs) of thin film Ba(Fe 1-x Co x) 2 As 2 bicrystals is strongly depressed, similar to high-T c cuprates. Our results suggest that weak-linked GBs are characteristic of both cuprates and pnictides because of competing orders, low carrier density, and unconventional pairing symmetry.
