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Optimizing 2212 with Overpressure (OP) Processing
Eric Hellstrom, Matt Boebinger, Ernesto Bosque, Peng Chen, Anca-Monia Constantinescu, Erin Flagler, Jianyi
Jiang, Tak Kametani, Hom Kandel, Jun Lu, David Larbalestier, Maxime Matras, Ulf Trociewitz
Applied Superconductivity CenterNational High Magnetic Field Laboratory
Florida State University
WAMHTS-1 – Hamburg, Germany – May 21-23, 2014
Funding: DOE-HEP, NSF-DMR, State of Florida
Collaborations with BNL, FNAL, LBNL, and OST
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Overview
• Why 2212 needs overpressure (OP) processing• JE is now useful for accelerator magnets• Questions that drive research at ASC• Update on OP furnaces at ASC
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Removing bubbles with overpressure (OP) processing more than doubles JE
0 20 40 60 80 1000
200
400
600
800
1000
1200
W13
W7
J E (4.2
K, 5
T), A
/mm
2
Total pressure (bar)
Closed-end wire @ 1 bar OP = long coil
Closed-end wire @ 100 bar OP
~2.5x~6-7x
Short open-end wire
JE = 725 A/mm2 @ 20 T
Gas-filled bubbles due to powder being only 60-70% dense
Squeeze wire to remove bubbles
Kametani, Jiang, Matras, Craig
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JE = 725 A/mm2
High Jc and JE in OP wire (4.2 K, 20 T)JE = 640 A/mm2 Jc = 2500 A/mm2
Lee and Dalban-Canassy
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Lee and Dalban-Canassy
High Jc and JE in OP wire (4.2 K, 20 T)JE = 640 A/mm2 Jc = 2500 A/mm2
JE = 725 A/mm2
Jc = 2900 A/mm2
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What can happen to 2212 filaments during melt processing?
Maximum packing density of 2212 powder in filaments is 60-70%Focus on the 30-40 vol% of the filament that is gas-filled void space
60% dense 2212 powder in green wire
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Kametani
1 bar – clean powder, no CO2, H2O
Best case with 1 bar processing: 30-40% gas bubbles in filament
Scheuerlein
60%
den
se
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Real-time, in situ x-ray microtomography shows how bubbles form and grow during heat treatment
Scheuerlein
Video shows filaments in 2212 wire during heating and cooling in 1 bar air
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1 bar – dirty powder: CO2, H2O
Worst case with 1 bar processing: dedensification and leakage
Scheuerlein• Malagoli• Shen
Internal gas pressure expands filament hole
60%
den
se
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100 bar – dirty or clean powder
Best processing: apply overpressure to squeeze Ag so filament hole
matches 2212 volume 100% dense
Scheuerlein
External overpressure decreases filament hole
60%
den
se
OP decreases wire diameter
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1 bar – clean powder:
no CO 2, H 2O
60 v
ol%
mel
t40
vol
%
gas
100 bar – dirty or
clean powder
100
vol%
mel
t75
vol
% g
as25
vol
%
mel
t
1 bar – dirty powder: CO2, H2O
60%
den
se
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Questions driving our 2212 studiesIn some cases we repeat earlier studies now using OP processed (dense) samples.• Is there any clear evidence that one powder is better than
another?• How uniform along the length does OP leave the samples?• Do billets with less C and H require lower OP pressure?• What is the optimum filament diameter (df) for optimum Jc?• Can we do a better ODS on both Ag/Mg and Ag/Al than we
are doing at present?• How do we measure powder quality?
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1 - Q: Is there clear evidence that one powder is better than another?
4.2 K, 5 T 37x18 wires100 bar OP
Matras, Jiang, Craig
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1 - Q: Is there clear evidence that one powder is better than another?
A: Nexans granulate gives highest JE after OP processing.
All these wires have 37x18. But 85x7 wire with standard powder is comparable with W7.
4.2 K, 5 T 37x18 wires100 bar OP
Matras, Jiang, Craig
Potential new powder sources• Metamateria• nGimat• SMS
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2 - Q: How uniform along the length does OP leave the samples?
A: Ic across 1 m sample shows 1.1% standard deviation
Matras, Jiang, Craig, Kandel
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OPed 2212 coil at 10 bar - generated 2.6 T in 31.2 T background = 33.8 T
Coil Terminal
15 mm TiO2Dielectric coating
71.2 mm36
.3 m
m
Wire Diameter = 1.4 mm
10 bar OP processing• Pressure was only high enough to prevent wire
from expanding• Did not compress Ag sheath and remove bubbles• Insulation - ~15 mm thick TiO2
Trociewitz
Bi01-12-Coil Projection as built:Wire dia. (mm): 1.40 Jw (Winding) (A/mm^2): 212.8nGimat Insulation (mm): 0.015 Je (A/mm^2): 285.8Turn-turn non-tightness (mm): 0.085 Io (A): 440.0layer-layer tightness (mm): -0.065 B [mT]: 2743.4Inner Radius (a1) (mm): 7.25 Coil Constant (mT/A): 6.2Outer Radius (a2) (mm): 18.17 L (mH): 0.8Height (2b) (mm): 71.21 Total Field Energy (J): 78.9Radial Layers (-): 8Turnss/Layer (-): 47Total turns (-): 376Conductor Length (m): 30.03
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3 - Q: Do billets with less C and H require lower OP pressure?A: No marked difference in densification at 25 bar between
high and low C + H wire
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Dirty Clean
CleanClean
Matras, Jiang, Craig
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85x7
4 – Q: What is the optimum filament diameter (df) for optimum transport Jc?
A: Jc decreases with decreasing diam in 27x7 wire with discrete filaments. Inconclusive for wires with extensive bridging.
27x7
Matras, Jiang, Craig
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5 – Q: How do we measure powder quality?A: No specific answer yet.
• Overall composition• Phase assemblage• Purity – no extra chemical species (Ba, Fe …)• C and H (and S) content – gas formers• Particle shape and size distribution• The gold standard for powder quality is Jc and JE in wire.
– Build subscale, multifilamentary wires.
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Update on OP furnaces at FSU
Max pressure
Hot Zone Type of heating CommentsDiameter Length
100-200 bar 25 mm 10 cm Hot wall (external)
Will be used for PhD studies
25 bar 48 mm 10 cm Hot wall (external) In use
75-120 bar 45 mm 25 cm Hot wall (external)
Starting to be used regularly
100 bar 170 mm 50 cm Cold wall (internal) Commissioning
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100 bar OP furnace for large coilsHot Zone:
16 cm , 50 cm
• Controlling uniform hot zone• Maintaining total pressure in system• Measuring and controlling pO2 during
heat treatment• Mixing gases in chamber during heat
treatment
Furnace is being commissioned
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Summary
• Overpressure processing makes 2212 a viable candidate for accelerator magnets– Round wire geometry– JE(B, )– Flexible, multifilamentary architecture– Can be easily cabled
• Rutherford• 6-on-1
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