Better conductors for 16-20 T
dipoles?
David Larbalestier
Applied Superconductivity Center, National High Magnetic Field
Laboratory, Florida State University, Tallahassee FL USA
(special thanks to Lance Cooley (FNAL), Dan Dietderich (LBNL),
Arno Godeke (LBNL) , Peter Lee (ASC), Mark Rikel (Nexans), Venkat
Selvamanickam (TcSUH), Mike Sumption (OSU), Chiara Tarantini
(ASC), and Aixia Xu (TcSUH) for input for this talk)
(And Bruce Strauss for yesterday’s talk)
Future Circular Collider Workshop
UniMail, University of Geneva, Geneva Switzerland
February 12-14, 2014
Supported by DOE-HEP, NSF, State of Florida and CERN
Slide 1
David Larbalestier, Future Circular Colliders Workshop, Geneva CH, February 12-14, 2014
Key points – work required!
Three possible conductors (5 years)
New and very much improved Nb3Sn
Further developed round wire Bi-2212
Cable-friendly REBCO coated conductors
Three long shots (10 years)
Round wire REBCO (2212 analog)
Round wire Fe-base superconductor
MgB2 with in-grain scattering for high
vortex pinning and Hc2 enhancement
Slide 2
David Larbalestier, Future Circular Colliders Workshop, Geneva CH, February 12-14, 2014
Magnet Conductors so far….
1. Nb47Ti conductor- thousands of 8 mm
diameter Nb47Ti filaments in pure Cu (0.8 mm
dia.), easily cabled to operate at 10-100 kA
20mm Cu
< 0.1 mm
2 mm Ag
1 mm HTS
~ 30 nm LMO
~ 30 nm Homo-epi MgO
~ 10 nm IBAD MgO
50mm Hastelloy substrate
20mm Cu
3. REBCO coated conductor – extreme texture (single
crystal by the mile) – for maximum GB transparency
4. Bi-2212 – high Jc without macroscopic texture!
2. Bi-2223 – the first HTS conductor – uniaxial texture
developed by deformation and reaction
Slide 3
David Larbalestier, Future Circular Colliders Workshop, Geneva CH, February 12-14, 2014
Isotropic, multifilament 2212 has higher
conductor Jc than coated conductor!
Requires ~100 bar 890°C
processing
High Jc, high Je and high Jw
has been demonstrated in a
coil already (2.4T in 31T)
Much less field distortion
from 2212 than from coated
conductors – better for high
homogeneity coils
7 times increase in long
length Je by removing
bubbles
~1900
A/mm2
in 2212
+
2212
(25% sc)
REBCO coated conductor (1% sc)
4
Slide 4
David Larbalestier, Future Circular Colliders Workshop, Geneva CH, February 12-14, 2014
Accelerator use demands strong vortex
pinning forces (Fp = Jc x B)
Depinning from a discrete
normal (N) or insulating (I) pin is
better than shear along a
continuous channel (e.g. GB)
which must be at least a weak
superconductor (S or S’) to
transmit supercurrent
I pins are better than N or S’ pins
because the pinning energy scale
is then the full condensation
energy
High Hc2 or irreversibility field
Hirr tilts the pinning force curve
to high field
A high density of strong pins
pushes to full summation of
individual pinning forces (fp) so
that Fp ~ n fp
Slide 5
Multifilamentary Cu/Nb-Ti
Composite SSC Type Strand
in Transverse Cross-Section
Equilibrium Fluxoid
Spacing at 5T, 4.2K
Meingast, Lee and DCL,
J. Appl. Phys. 66, 5971
David Larbalestier, Future Circular Colliders Workshop, Geneva CH, February 12-14, 2014
Nb-Ti optimizes both fp so that Fp ~ n. fp
20
ef
Finer and more densely
packed precipitates
e = 5.3
f
18
16
e f = 4.4
Fp (G N/m3 )
14
e f = 3.4
12
10
e f = 2.5
8
6
e f = 1.1
4
2
0
0
1
2
3
4
5
6
7
8
9
10 11
B (T)
Without a-Ti precipitates, only weak GB pinning occurs
a-Ti precipitates start as normal metal (N) pins but become
weakly superconducting (S’) when optimized because their
high density outweighs their declining pinning strength
At optimum, a-Ti pin density n is several times vortex density
Slide 6
David Larbalestier, Future Circular Colliders Workshop, Geneva CH, February 12-14, 2014
What does Nb3Sn need?
Nb3Sn has sparse and weak vortex
pinning by grain boundaries that
allows flux sliding along the whole GB
network
What can be done?
Strengthen pinning by increasing the
superfluid density (Tarantini ASC-NHMFL)
Adding point pins (Dietderich LBNL)
Restricting grain growth (Sumption OSU)
Slide 7
David Larbalestier, Future Circular Colliders Workshop, Geneva CH, February 12-14, 2014
GB pins- 30-50 times lower pin
density than Nb-Ti
RRP
620°C / 192h
SEM
Fractographs
A15 % of non-Cu
Grain size / GB density
A15 layer Jc
QGB=Fp/SGB
Peter Lee’s SEM images in Tarantini et al. arXiv 1310.6729, to appear SuST 2014
Slide 8
David Larbalestier, Future Circular Colliders Workshop, Geneva CH, February 12-14, 2014
2700
2400
2100
From VSM data
12 T
1200
16 T
1100
Jc(16T) first increases at medium-high
temperature (680-695°C) before dropping at
750° C, even as the diffusion barriers break
badly and leak large amounts of Sn
1000
900
4.2K
62
0°
C/
19
2h
65
0°
C/
96
h
66
5°
C/
50
h
68
0°
C/
48
h
69
5°
C/
48
h
75
0°
C/
96
h
2
Jc (12T) is dominated by small grain size even
though HT at lower temperature leaves lots of lowSn, low Hc2 A15 present. Higher T HT helps Hc2,
even as it causes grain growth
3000
Non-Cu Jc @ 16T (A/mm )
2
Non-Cu Jc @ 12T (A/mm )
Jc(16T) can be enhanced by HT reaction
(RRP 54/61) – but not to 2000 A/mm2
Slide 9
Strauss (FCC talk Thursday) – we
want 2000 A/mm2 at 15 T
David Larbalestier, Future Circular Colliders Workshop, Geneva CH, February 12-14, 2014
The unit pinning force exerted by GBs on
vortices increases as HT increases
Pinning energy scale is  Tc distribution
2
2
A15 layer-QGB @ 16T (N/m ) A15 layer-QGB @ 12T (N/m )
Vortex pinning strength, QGB(16T) is
strongly
enhanced
by
high
HT
temp.
10000
9500
12 T
9000
8500
+35%
8000
0.20
7500
Nb3Sn
m0H = 16 T
96h
750°C
0.30
16 T
0.15
0.25
48h
695°C
0.10
48h
680°C
0.05
16 T
0.00
750°C
HT T
0.05
680°C
emp
ur e
4000
665°C
erat
+68%
192h
620°C
650°C
620°C
2
4
6
8
10
Tc (K)
4.2K
62
0°
C/
19
2h
65
0°
C/
96
h
66
5°
C/
50
h
68
0°
C/
48
h
69
5°
C/
48
h
75
0°
C/
96
h
3000
Slide 10
0.15
0.10
50h
665°C
96h
650°C
695°C
From VSM data
0.20
f(Tc)
7000
6000
5000
0.25
Higher T reactions require better
diffusion barriers (RRP 54/61)
David Larbalestier, Future Circular Colliders Workshop, Geneva CH, February 12-14, 2014
12
0.00
8
% React-through
The minimum to be done
for high Jc (16T)
Average All Ring
1st Ring (Inner)
2nd Ring
3rd Ring (Outer)
3rd Ring - Corner
3rd Ring - Non Corner
10
1
0.1
0.01 (a)
100
50
100
150
200
250
300
350
400
RRR
(b)
10
1
0.1
0.01
Mean Barrier Thickness (mm)
62
0°
C/
19
2h
Raises the superfluid density f(Tc) and
the energy scale for fp
0
% React-through, % <0.5mm
Raise Hirr by pumping in as much
Sn as possible
(c)
1.4
1.2
75
0°
C/
96
h
69
5°
C/
48
h
68
0°
C/
48
h
0.6
66
5°
C/
50
h
0.8
Average All Row
1st Row (Inner)
2nd Row
3rd Row (Outer)
3rd Row - Corner
3rd Row - Non Corner
65
0°
C/
96
h
1.0
Heat Treatment
Strengthen barriers –
RRR degrades for only 12% of barrier breakdown
Slide 11
David Larbalestier, Future Circular Colliders Workshop, Geneva CH, February 12-14, 2014
Or, add insulating pins to get a full
condensation energy pinning
Fine grains (~50 nm with insulating
(I) Al2O3 pins) drives high Jc and Fp
curve into Nb-Ti form
The problem: these are thin films
and so far ppts. in FM conductors
have been elusive
2000 A/mm2 at 16 T is clearly within
reach
Slide 12
David Larbalestier, Future Circular Colliders Workshop, Geneva CH, February 12-14, 2014
Nb3Sn Conductors with Grain size reduction and Fp,max shift
Xu, Sumption, Peng, Collings Appl. Phys. Letts submitted
What (Aim)?: To increase Jc at 15 T, 4 K in Nb3Sn, increase Bc2, or increase flux pinning. Here we focus on
pinning, by; (1) Fp, or (2) a shift of Fp,max from 0.2 Birr to 0.3 to 0.5 Birr. We will use Grain size refinement.
Why?: If the Nb3Sn grain size (in films) is refined to 15-30 nm, the peak of the Fp-B curve is shifted to 0.5Birr,
improving the 12 T Jc by a factor of three [D. R. Dietderich and A. Godeke, Cryogenics 48, 331 (2008)]
How?: Grain size ↓ by HT Temp ↓ have hit the limit (further T ↓ reduces Sn %). But Rumaner [Metall. Mater.
Trans. A 25, 213 (1994)] used internally oxidized Zr to reduce grain size in films. Zeitlin attempted to transfer to
strands [IEEE Trans. Appl. Supercon. 15, 3393 (2005)], using internally oxidized Nb-Zr but did not see refinement.
(1) We exposed Nb-Zr/Sn wires (no Cu) to Ar- 45 nm Nb Sn grain size
3
Oxygen atmosphere during HT to internally
oxidize Zr and refine Nb3Sn grains – with success!
A ZrO2 particle
(a)
(b)
Fracture SEM images of samples reacted at 850 °C for 10 min in (a)
pure Ar and (b) Ar-O2 atmospheres.
This work was funded by the US Department of Energy,
Division of High Energy Physics, Grant No. DE-FG0295ER40900, and DE-SC0010312.
Slide 13
Average Nb3Sn grain
TEM image showing size as a function of
the ZrO2 particles reaction temperature
David Larbalestier, Future Circular Colliders Workshop, Geneva CH, February 12-14, 2014
Halved grain size (45 nm) shifts Fp and
provides relative Jc advantage
(2) Next Step, Subelement with internal oxidation: based
on a review of the Ellingham Diagram, we put SnO2 powder
between the Cu/Sn core and the Nb-1Zr tube wall:
For comparison, an analog with NbO2 was also
fabricated.
(a)
(b)
Nb-1Zr tube
Cu matrix
SnO2 powder
Cu
Sn core
10 μm
Ellingham Diagram
SEM image of the wire with SnO2, ready
to stack into multi-filament strands.
(a)
(b)
The Fp-B curves with SnO2 and NbO2 peak at ~0.3Birr
and ~0.2Birr, respectively.
•
•
Grain sizes of samples with (a) NbO2 and (b) SnO2, reacted at
650 °C for 150 h, are 91 and 43 nm, respectively.
The (a) Fp-B, and (b) reduced Fp-B curves of samples reacted
at 650 °C for 150 h (note Birr normalized Fp curve at right
indicates peak shift, distinct from Birr shift)
12 T layer Jc of the wire with SnO2 is ~6.1 kA/mm2, that for
Nb2O strand 5.4 kA/mm2 – both excellent, but in fact
suppressed by low Birr (20.5 T), because they are binary.
However, a ternary version should have a Birr of ~25 T, if so,
we estimate that the 12 T layer Jc should be significantly
higher (perhaps ~10kA/mm2).
Conclusion: in light of the results obtained, we anticipate that this approach could lead to substantial
improvement in the performance of Nb3Sn conductors – and is ready for ternary multifilament investigation
Paper submitted to Applied Physics Letters
Slide 14
David Larbalestier, Future Circular Colliders Workshop, Geneva CH, February 12-14, 2014
If Nb3Sn is plan A for a 100 TeV
LHC………….
Present RRP and PIT designs are unlikely to satisfy – the
lessons they teach are that higher T reactions with more
homogeneous Sn can raise Jc but that stronger diffusion
barriers are essential – max Jc may be 1200 A/mm2
Insulating pins and finer grains may get the required Jc –
layer Jc of ~5000 A/mm2 (non-Cu ~ half this) shown in thin
films
Fabrication of ppt-containing fine filaments has been
attempted by Supergenics, SupraMagnetics and most
recently Hypertech-OSU
…………….a focused program will be needed to
establish feasibility of a 16 T Nb3Sn conductor
Slide 15
David Larbalestier, Future Circular Colliders Workshop, Geneva CH, February 12-14, 2014
Plan B: 20 T requires HTS conductors
Je≈ 600 A/mm2
DCL et al.
Nature
Materials
accepted,
arXiv
1305.1269
20+ T
16
10 T T
Note that this is
600 A/mm2 (20T)
in a conductor
that is about 25%
2212, so layer Jc
is ~1800 A/mm2
REBCO tapes developed for electric utility applications (several hundred millions)
versus recent HEP-driven development (so far about $5M) for Bi-2212
Slide 16
David Larbalestier, Future Circular Colliders Workshop, Geneva CH, February 12-14, 2014
Round wire
Bi-2212
650
600
Ic(4.2K), A
Can Jc of round wire (RW)
2212 go higher? Almost
certainly……….
700
Field up
Field down
J. Jiang “Overpressure
processing as the route to high Jc
in coil length Bi-2212 round wires”
MT-23 July 14-20, Boston MA, USA
(2013)
550
500
450
Overpressure processing removes gas
bubbles but leaves high angle GBs in
place
However no hysteretic signature of weak
links as is quite obvious in Bi-2223
Bi-2212 phase field is broad, opening
up cation defect pinning
Recall that Bi-2212 is the first HTS
conductor like an LTS conductor
400
350
300
4.2K, H  wire
0
1
2
3
4
5
6
7
8
9 10 11 12 13 14 15 16
Applied Field (T)
Very
different in
Bi-2223
tape
twisted, multifilament, round, good normal
conductor in parallel – no Diffusion Barrier
needed
Bi-2212 RW is an ongoing effort of US BSCCo (Bismuth
Strand and Cable Collaboration at ASC-NHMFL, BNL, FNAL
and LBNL with OST and Nexans (under CERN support) and
in association with EUCARD2
Slide 17
[Ref. **] Martin et al., IEEE Trans.
Appl. Supercond., (1997)
David Larbalestier, Future Circular Colliders Workshop, Geneva CH, February 12-14, 2014
Challenge: understand 2212
phase – complex!
Mark Rikel (Nexans) in the lead (EUCARD2 and BSCCo association)
Slide 18
David Larbalestier, Future Circular Colliders Workshop, Geneva CH, February 12-14, 2014
Cables: Large magnets are better protected
when operated at high current– cables!
Easy path to 2212 cables
through the standard
Rutherford cable
REBCO cables are harder
(Coated Conductor is a
single filament) – but
possible (IRL, KIT, CORC,
twisted stack (MIT)
Cables vital for 60 T hybrid
at the NHMFL, an LHC
energy upgrade and a
neutrino machine based on
a Muon Collider at Fermilab
Bi-2212 Rutherford cables
(Arno Godeke LBNL) with
mullite insulation sleeve
REBCO coated conductor cable wound in
many layers helically on a round form
Other
variants too:
e.g. Roebel
cable
Danko van der Laan
Slide 19
David Larbalestier, Future Circular Colliders Workshop, Geneva CH, February 12-14, 2014
Plan C: REBCO vortex pinning engineering works –
MOCVD on IBAD substrates compatible with e.g.
Cable on Round Cores (CORC)
Strong recent developments in Selvamanickam group at TcSUH (Aixia
Xu et al. MT23 presentation)
Strongly enhanced vortex pinning from 4 to 77 K in magnetic fields up to 31 T in a 15 mol% Zradded (GdY)-Ba-Cu-O superconducting tapes - Xu, Delgado, Khatri, Liu, Selvamanickam (TcSUH) and
Abraimov, Jaroszynski, Kametani and Larbalestier (ASC-NHMFL) – in final draft
Slide 20
David Larbalestier, Future Circular Colliders Workshop, Geneva CH, February 12-14, 2014
The insulating vortex pins that
one would love in Nb3Sn too..
TEM by Kametani ASC-NHMFL
BaZrO3 and RE2O3 pins give REBCO the same
Jc properties as Nb-Ti
At 77K, not 4.2K
But layer thickness is 1 mm
3-5 mm REBCO and thinner substrates would go far to
equalize JE too
Pinning force at 4.2 K now exceeds 1500
GN/m3, 75 times Nb-Ti
Slide 21
David Larbalestier, Future Circular Colliders Workshop, Geneva CH, February 12-14, 2014
JE comparisons today clearly favor RW Bi-2212 –
Fine filament twisted
conductor is ideal for
high homogeneity NMR
and accelerator magnets
From the cover of the
MagSci report
(DCL et al. arXiv 1305.1269 – to
appear Nature Materials 2014)
Slide 22
Bi-2212 conductor support by DOE–OHEP: an outcome of
Bismuth Strand and Cable Collaboration (BSCCo)
David Larbalestier, Future Circular Colliders Workshop, Geneva CH, February 12-14, 2014
Making common cause across many
sectors is possible and desirable
http://www.nap.edu/catalog.php?record_id=18355
High Magnetic Field Science and Its
Application in the United States: Current
Status and Future Directions
(Halperin Chair
Met in 2012, report about to issue
Report released November 2013
Note the cover image! Bi-2212 developed under OHEP support!
Slide 23
David Larbalestier, Future Circular Colliders Workshop, Geneva CH, February 12-14, 2014
High Magnetic Field Science and Its
Application in the United States: Current
Status and Future Directions
The recommendations (Halperin (Harvard) Chair
Consider regional 32 T superconducting magnets at 3-4 locations
optimized for easy user access.
Establish at least 3 US 1.2 GHz NMR instruments (planned
commercial) for broad access and plan for ~1.5 GHz class system
development
Establish high field (~30 T) facilities at neutron and photon
scattering facilities
Construct a 20 T MRI instrument (for R&D)
A 40 T all‐superconducting magnet should be designed and
constructed,
A 60 T DC hybrid magnet that will capitalize on the success of the
current 45 T hybrid magnet at the NHMFL‐Tallahassee should be
designed and built.
Very strong synergy with HEP goals (LHC energy upgrade
and Muon Accelerator) for high field use – needs HTS strand
AND cable development
Slide 24
David Larbalestier, Future Circular Colliders Workshop, Geneva CH, February 12-14, 2014
Summary
16-20 T magnets require conductor development
Nb3Sn is probably still plan A, but:
New conductor concepts needed
Stability margin may be too small, so pointing to HTS……
HTS now has a round wire, multifilament, twisted,
good normal metal conductor (Bi-2212)
But it requires special processing
Strength properties uncertain
All HTS have quench protection issues
Specific solutions only – need general ones
Other sectors need HTS conductors too
NMR, MRI, Photon, neutron, national magnet labs
Slide 25
David Larbalestier, Future Circular Colliders Workshop, Geneva CH, February 12-14, 2014