Post on 27-Mar-2015
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Lattice structure and misfit between substrate/buffer/YBCO conductor
perovskiterocksaltfcc structurespinelfluoriteC-type REpyrochlore
Material Structure Tm/ oC a0 (300K) Lm
MisfitYBCO (%)
Misfit to Ni (%)
Misfit to NiO
(%)Ni fcc 1455 3.52 3.52 -9.38 0.00 -18.47
YSZ cubic / fluorite 2680 5.13 3.63 -6.06 3.03 -14.88
Gd2Zr2O7 cubic / pyrochlore 10.52 3.72 -3.49 5.38 -12.10
Y2O3 cubic / Mn 2O3 >2400 10.6 3.75 -2.67 6.13 -11.20
LaAlO3 rhombohedral / perovskite 2100 5.36 3.79 -1.58 7.12 -10.03
La2Zr2O7 cubic / pyrochlore 2300 10.8 3.81 -1.05 7.61 -9.45
Gd2O3 cubic / Mn 2O3 >2400 10.81 3.82 -0.79 7.85 -9.16
CaTiO3 orthorhombic / perovskite 5.38x5.44 3.82 -0.79 7.85 -9.16
CeO2 cubic / fluorite 2600 5.41 3.83 -0.52 8.09 -8.88
Eu2O3 cubic / Mn 2O3 >2300 10.87 3.84 -0.26 8.33 -8.59
LaNiO3 rhombohedral / perovskite 5.45 3.84 -0.26 8.33 -8.59YBCO orthorhombic 3.83x3.88 3.85 0.00 8.57 -8.31
Ca0.6Sr0.4TiO3 orthorhombic / perovskite 5.46x5.46 3.86 0.26 8.81 -8.03
NdGaO3 orthorhombic / perovskite 1670 5.43x5.5 3.86 0.26 8.81 -8.03
Sm2O3 cubic / Mn 2O3 >2300 10.93 3.86 0.26 8.81 -8.03
La2NiO4 tetragonal 3.86 3.86 0.26 8.81 -8.03
Sr2RuO4 tetragonal 3.87 3.87 0.52 9.04 -7.75LSMO rhombohedral / perovskite 5.49 3.88 0.77 9.28 -7.47NdBCO orthorhombic 3.87x3.92 3.89 1.03 9.51 -7.20
Pd fcc 1555 3.89 3.89 1.03 9.51 -7.20
Gd2CuO4 tetragonal 3.89 3.89 1.03 9.51 -7.20
SrTiO3 cubic / perovskite 2080 3.91 3.91 1.53 9.97 -6.65
LaMnO3 orthorhombic / perovskite 5.54x5.74 3.91 1.53 9.97 -6.65
Nd2O3 cubic / Mn 2O3 >2300 11.08 3.92 1.79 10.20 -6.38
SrRuO3 orthorhombic / perovskite 5.57x5.54 3.93 2.04 10.43 -6.11
Nd2CuO4 tetragonal 3.94 3.94 2.28 10.66 -5.84
BaTiO3 tetragonal / perovskite 3.99 3.99 3.51 11.78 -4.51Ag fcc 961 4.09 4.09 5.87 13.94 -1.96
SrZrO3 orthorhombic / perovskite 2800 5.79x5.82 4.10 6.10 14.15 -1.71
BaSnO3 cubic / perovskite 4.12 4.12 6.55 14.56 -1.21NiO cubic / rocksalt 1984 4.17 4.17 7.67 15.59 0.00
BaZrO3 cubic / perovskite 2690 4.19 4.19 8.11 15.99 0.48MgO cubic / rocksalt 3100 4.21 4.21 8.55 16.39 0.95TiN cubic / rocksalt 4.24 4.24 9.20 16.98 1.65
Conductive
buffer layers
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B.A.Glowacki
Twisted conductor
- the filaments must be transposed (or twisted) at least one time in the middle of the length provided that the magnetic field is exactly symmetric along both half lengths
-twisted decoupled filaments - ac loss reduction coefficient
- large circulating currents can exist among the filaments due to connections at the ends (in current leads)
-ac losses may increase by one order of magnitude or more in dependence on the distance between the filaments and the resistance at the end.
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3) multifilamentary tapes in a transverse magnetic field
- hysteresis losses in perpendicular magnetic field - about 2-3 orders ofmagnitude higher than in parallel field
Ho - amplitude of the applied magnetic field
w - tape width t - tape thickness
-for decoupled filaments - ac loss reduction directly proportional to the number of filaments (proved experimentaly)
Ho
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Initial design of multifilamentary CC for Supergenerator
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Multifilamentary YBa2Cu3O7 Coated Conductor
CC-20 filaments CC-1filament
1cm
Single filament < 500m
IRC in Superconductivity testing
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B.A.Glowacki
AC field AC current anisotropy at the IRC in Superconductivity
Magnet requirement for YBCO coated conductors in supergenerators is about 2T/400 Hz
QI/Q||~100 (high precision of angle required in parallel field - of the order of 0.1 degree)
Current AC magnet capability
In phase and out of phase measurements for transformers and generators
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Division to smaller filaments essential for Ha perp. to ab plane
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Transport critical current vs angle + Ca doping
102
103
104
105
106
107
0 2 4 6 8 10
grain2 deg4.5 deg7 deg15 deg20 deg24 deg
Cri
tica
l cu
rren
t de
nsit
y J
c (A
cm-2)
Magnetic field oH (Tesla) 102
103
104
105
106
107
0.0 10 20 30 40
BulkThin filmLPE
Cri
tica
l cu
rren
t J
c (A
cm-2)
Angle (degrees)
30
40
50
60
70
80
90
100
0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1
Y0.8Ca0.2Ba2Cu3O6+xYBa2Cu3O6+x
Cri
tical Te
mp
era
ture
Tc
(K)
Oxygen content, x
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Current percolation through the dislocations
I
Important factors:
• conductor aspect ratio • magnetic field angle • sample history • shunt layers, contactswidth
length
4Å
HREM of LAGB
[N.D. Browning et al, Micron 30, 425 (1999)]
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Ap
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hInfluence of misoriented Ni grains on YBCO layer
CuO precipitates
NiO layer grown by surface oxidation epitaxy
CSTO grown by PLD via an amorphous route
YBCO grown by PLD
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0
0.05
0.1
0.15
0.2
0.25
1 10 100 1000 10000
Length (no. of grains)
Jc/J
c0
w=3
w=5
w=9
w=17
w=33
w=129
w=513
1 filament
5 filaments
11 filaments
Recommended division of the coated conductors to narrower tracks/filaments is a compromise between reduction of the current in the longer tracks and gain in reduction of AC losses.
w
l
Transport direction
2° 4° 6° 8°
The EBS maps above show regions misoriented by 2°, 4°, 6°, and 8° in a small area of the NiFe substrate.
Using a model with a 2D array of R rows and C columns of hexagonal grains (shown above left), a number of parameters may be assessed over a range of threshold angles.
Current percolation in In-plane and out of plane misoriented GB
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B.A.Glowacki
p=5
p=1
A New Grain Structure Model
MCS = 2 MCS = 25 MCS = 100
A Monte-Carlo grain growth model has been used to simulate more realistic grain structures. The grains are initially made up of single square pixels.
Each pixel has an energy based upon the number of neighbours which are in the same grain.
High energy pixels are consumed by neighboring grains.
As the simulation progresses, grain structures such as those below develop.
After N Monte-Carlo Steps (MCS) each pixel will, on average have been considered N times.
The average grain size in pixels (p) is related to MCS. The figures above shows grain structures for p=1 (simple square model) and p=5, both for samples 25 grains long and 10 grains wide.
2-D Grain growth modelling IBAD and RABIT
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Ic vs length and width of Coated Conductor
Ic (1/NL)1/NW
… a useful working approximation is
10 km1 cm
NL NW
Ic
102
104
106
108102
104
[Rutter and Goyal MRS 2003]
Nw=300 grains
Nw=100 grains
Nw=30 grains
Nw=10 grains
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Orientation of the GB in respect to the applied magnetic field is important
In plane critical current vs magnetic field measurements on YBCO thin films: (a) angular dependence of the critical current crossing low angle grain boundary at 8T. For the higher GB angle the minimum is wider and the absolute valuses are substantially lower; =90o represents Lorentz force-free configuration. Hexagons represent grains whereas black outlines of hexagons represent
grain boundaries; (b) schematic of the Jc vs (B,) in plain measurements.
Elongated hexagonal grains have the better percoative properties than the simple hexagonal ones. There is a difference in the response of hexagonal grains if all of them are aligned.
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Solution for the high magnetic field and low temperature magnet applications
NbTi + Nb3Sn + NbTi3(Sn,Ta) = 22.59T additional magnetic field generated by Bi-2212 coil = 1.46T ; total field > 24T
YBa3Cu2O7 B
I
High magnetic field superconducting electromagnet. (a) schematic cross section of the multi-section hybrid electromagnet. The materials used are NbTi + Nb3Sn + NbTi3(Sn,Ta) resulting in
22.59 Tesla and if additional magnetic field is generated by internal coil in the centre it would generate an additional field. The total magnetic field in such a hybrid configuration, currently exceeds 24 Tesla. (b) schematic outline of the favourable grain structure of the internal HTS coil
made from the YBa2Cu2O7 coated conductor.
(a) (b)
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B.A.Glowacki Presence of the magnetic material can have a detrimental and also beneficial influence on the reduction of AC losses and increase of Jc of superconductors. This problem is particularly important in case of the coated conductors and multifilamentary wires. The latest research on the multifilamentary conductors surrounded by magnetic material proved that losses can be reduced substantially according to eq.1 by coating individual filaments by magnetic material.
By comparing losses in a standard multifilamentary superconductor, Qst, to losses in a multifilamentary superconductor with the magnetic covers around individual filaments, Qcov, at the same reduced current i, one can obtain magnetic decoupling loss reduction coefficient, Kmd, (eq.1); where i=I/Ic Ic1=Ic/N, N number of filaments. The parameters k(i) and are to be determined from experiment and represent individual filament.
K md Q stQ cov
I c
2 F i Nk i a 2 I c 1
2 F i
N 2 I c 12
Nk i 2 I c12 N
k i 2 (eq.1)
3) multifilamentary tapes in a transverse magnetic field
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Minimisation of AC losses Magnetic decoupling
0
0.05
0.1
0.15
0.2
0.25
1 10 100 1000 10000
Length (no. of grains)
Jc/J
c0
w=3
w=5
w=9
w=17
w=33
w=129
w=5131 filament5 filaments11 filaments
0
0.001
0.002
0.003
0.004
0.005
0.006
0.007
0.008
0 2 4 6 8 10 12
Ac loss
(Jm-1
)
Number of filaments
0.25mW/Am
0.45mW/Am
1.7 mW/Am !
Recommended division of the coated conductors to narrower tracks/filaments is a compromise between reduction of the current in the longer tracks and gain in reduction of AC losses.