RADIATION EFFECTS ON HIGH
TEMPERATURE SUPERCONDUCTORS
Harald W. Weber
Atominstitut, Vienna University of Technology
Vienna, Austria
From ITER to DEMO
Neutron Spectra
Neutron-induced Defects in HTS
Practical Materials
HTS4Fusion Conductor Workshop, KIT, 27 May 2011
LOW TEMPERATURE PHYSICS
From ITER to DEMO
ITER
DEMO
HTS Magnets ?
YBCO,
BiSCCO, MgB2
•
The cooling power could be significantly reduced.
•
The radiation shields could be significantly reduced and simplified.
•
Higher magnetic fields could be achievable.
•
Smaller coil geometries would become feasible.
•
Could He be replaced?
LOW TEMPERATURE PHYSICS
Options / Materials
“Demo” design (magnetic field, temperature, fluence)
• Cheaper: MgB2
• Higher fields: HTS
Bi-2212: ≤ 10 K
Bi-2223: ≤ 20 K
Coated conductors (RE-123): ≤ 50 K
• Higher temperatures:
Coated conductors (RE-123) ~ 65 -77 K
LOW TEMPERATURE PHYSICS
NEUTRON SPECTRA
Production of 14 MeV neutrons – deposition of energy in the “first wall” 
substantial material problems (~1 MW/m²)!
At the magnet location: Attenuation by a factor of ~ 106. Scattering processes
lead to a “thermalization” of the neutrons!
The lifetime fluence of the ITER magnets amounts to 1 x 1022 m-2 (E > 0.1 MeV)
LOW TEMPERATURE PHYSICS
LOW TEMPERATURE PHYSICS
DAMAGE ENERGY SCALING
(E)
neutron cross section
T(E)
F(E)
t
primary recoil energy distribution
neutron flux density distribution
irradiation time in the neutron spectrum F(E)

< (E) . T(E) >
displacement energy cross section
ED = < (E) . T(E) > . F(E) . t damage energy (total energy transferred to each
atom in the material)
SUCCESSFUL SCALING OF Tc AND Jc IN METALLIC SUPERCONDUCTORS

PREDICTIONS OF PROPERTY CHANGES IN AN UNAVAILABLE NEUTRON
SPECTRUM ARE FEASIBLE!
LOW TEMPERATURE PHYSICS
DAMAGE PRODUCTION in SUPERCONDUCTORS
FAST NEUTRONS (E > 0.1 MeV)
Displacement cascade initiated by the primary knock-on atom, if
its energy exceeds 1 keV
EPITHERMAL NEUTRONS (1 – 100 keV)
Point defect clusters
THERMAL NEUTRONS
Transmutations, point defects
-rays: No influence
HTS: Fast neutrons produce stable collision cascades because of
their low conductivity
LOW TEMPERATURE PHYSICS
Neutron-induced Defects in HTS
STATISTICALLY DISTRIBUTED
~ SPHERICAL, ~ 2.5 nm Ø
SURROUNDED BY A STRAIN FIELD
OF THE SAME SIZE
22
-3
22
-2
5 x 10 defects m per 10 neutrons m
FAST NEUTRONS (E>0.1 MeV)
COLLISION CASCADES,
IF THE ENERGY OF THE
PRIMARY KNOCK-ON
ATOM EXCEEDS
 1 keV
M. Frischherz et al.: Physica C 232, 309 (1994)
LOW TEMPERATURE PHYSICS
YBa2Cu3O7- - Y-123
LOW TEMPERATURE PHYSICS
CONSEQUENCES FOR THE PRIMARY SUPERCONDUCTIVE PROPERTIES:
Introduction of disorder – mainly O-displacements
92
transition temperature (K)
91
90
89
88
87
0
2
4
6
8
10
12
14
16
18
21
20
22
-2
fast neutron fluence (10 m )
M. Eisterer et al.: Adv. Cryog. Eng. 46, 655 (2000)
F.M. Sauerzopf: PRB 57, 10959 (1998)
LOW TEMPERATURE PHYSICS
Consequences for flux pinning
H || c
H || a,b
LOW TEMPERATURE PHYSICS
The same defects act differently in different materials
c-axis
Example: parallel columnar defects
Y-123 (“3D”): Peak for H parallel to columns
Bi-2212 (“2D”): Reduction of Jc anisotropy
M. Kraus et al.: Phys. Bl. 50, 333 (1994)
LOW TEMPERATURE PHYSICS
(Am-2)
Experimental Jc data
1x1021m-2
8x1021m-2
F.M. Sauerzopf: PRB 57, 10959 (1998)
LOW TEMPERATURE PHYSICS
Model defects in “2D” Bi-2223 tapes
Connolly et al., TU-Delft 2000
LOW TEMPERATURE PHYSICS
Critical Currents at 77 K
19
2
Jc (A/m )
unirr.
10
8
10
7
10
6
10
5
3*10 m
-2
HIIab
HIIc
80
18.5
0
1
2
3
4
5
6
µ 0 H (T)
S. Tönies et al.: IEEE Trans. Appl. Supercond. 11, 3904 (2001)
LOW TEMPERATURE PHYSICS
Irreversibility Lines
H||ab
6
unirr.
18
6*10 m
5
-2
19
1.2*10 m
µ0H(T)
4
19
-2
19
-2
2*10 m
3*10 m
3 H ||c
19
5.5*10 m
-2
-2
unirradiated
2 6*10 18 m -2
19
1.2*10 m
-2
1 2*10 19 m -2
19
0
3*10 m
19
-2
5.5*10 m
40
-2
50
60
70
80
90
100
T(K)
LOW TEMPERATURE PHYSICS
Y-123: Similar behavior of fission tracks
and collision cascades
Fission Tracks
Collision Cascades
10
10
5K
-2
Jc(Am )
30 K
9
10
50 K
60 K
8
10
70 K
77 K
0
2
4
6
8
10 12 14 0 2 4
B (T)
6
8
10 12 14
M. Eisterer et al.: SUST 11, 1001 (1998)
LOW TEMPERATURE PHYSICS
SUMMARY: NEUTRON - INDUCED DEFECTS
• “3D” HTS:
Strong pinning of flux
lines for H || c
Reduced intrinsic pinning
through disorder (H || a,b)
• “2D” HTS:
Pinning of a few individual
pancakes
Reduced intrinsic pinning
through disorder (H || a,b)
LOW TEMPERATURE PHYSICS
PRACTICAL MATERIALS
4 HTS compounds suitable for fusion applications
1)
MgB2 (Tc ~ 39 K)
Low temperature (5 – 10 K) and intermediate field (< 10 T) application (PF)
2)
Bi-2212 (Tc ~ 87 K)
ITER like fields up to 25 K (intrinsic limit)
3)
Bi-2223 (Tc ~ 110 K) – 1G conductors  are now being replaced by RE123 coated (2G) conductors
ITER like fields up to 30 K (intrinsic limit)
4)
RE-123 (Tc ~ 92 K)
ITER like fields up to 60 K, higher T operation possible
Magnetic field applications at T > 50 K only with RE-123 HTS compounds
LOW TEMPERATURE PHYSICS
MgB2 Wires
Pure MgB2 is anisotropic: = Hc2ab/Hc2c ~ 5
Grains are randomly oriented:
different upper critical fields in different grains!
Distribution function:
0.40
relative abundance
0.35
0.30
0.25
0.20
0.15
0.10
0.05
0.00
3
Bc2
4

5
6
7
8
9
Bc2(T)
10
11
12
13
14
Bc2
||
M. Eisterer et al.: JAP 98, 033960 (2003)
LOW TEMPERATURE PHYSICS
“Irreversibility line” can be shifted by an increase of Bc2 and / or by a reduction
of the anisotropy:
B 0 

1
2

 1 pc2  1
Bcab2
M. Eisterer et al.: JAP 98, 033960 (2003)
Neutron irradiation increases Bc2 and decreases .
14
12
B (T)
10
8
6
undamaged
4
2
irradiated
Bc2
B=0
0
0
5
10
15
20
25
30
35
40
T (K)
LOW TEMPERATURE PHYSICS
Neutron irradiation:
Bc2 ↑
B=0 ↑
Jc(B) ↑ at high magnetic fields
1000
Cu-sheathed wire
unirradiated
22
-2
2x10 m
9
100
Ic (A)
-2
Jc (Am )
10
8
10
10
7
10
0
2
4
6
0H (T)
8
10
Introduction of defect cascades is less important, grain boundary pinning is dominant !
M. Eisterer et al.: SUST 15, 1088 (2002)
LOW TEMPERATURE PHYSICS
Critical currents can be fully explained by a percolation
model (solid lines)
2
Jc(A/m )
10
9
10
8
10
7
10
6
10
5
10
4
unirr.
irr.
bulk (5 K)
wire (4.2 K)
0
2
4
6
8
10
B(T)
12
14
16
18
1.79
 p ( J )  pc 

J c ( B )   
 1  pc 
dJ
M. Eisterer et al.: Phys. Rev. Lett. 90, 247002 (2003)
LOW TEMPERATURE PHYSICS
EXTRAPOLATED PERFORMANCE at 4.2 K
11
10
10
10
Bc2=74 T, =1.85
9
-2
Jc(Am )
10
8
10
Bc2=55 T, =3.2
7
10
Bc2=40 T, =4.3
6
10
5
10
0
5
10
15
20
25
30
35
40
B(T)
LOW TEMPERATURE PHYSICS
Coated conductors
Focus on commercial tapes
LOW TEMPERATURE PHYSICS
Microstructure
Key elements:
•
JcGB (grain boundaries – inter-grain
currents)
– relevant at small fields
– grain boundary angle
– doping
•
JcG (grains – intra-grain currents)
– relevant at high fields
– pinning centres
•
Jc vs. field orientation
•
Homogeneity along (long) lengths
current
LOW TEMPERATURE PHYSICS
Irreversibility Lines
64 K
16
77 K
coated conductors
µ0H||c
µ0H||ab
14
H||c
AMSC
5.6 T
Bruker
7.7 T
Sumitomo
1.15 T
10
µ0H (T)
77 K
BSCCO multifilament tape
µ0H||c
µ0H||ab
12
8
6
4
2
0
50
55
60
65
70
75
80
85
90
95
100
105
110
T (K)
LOW TEMPERATURE PHYSICS
4x10
10
2x10
10
-2
Jc (Am )
Neutron irradiation
10
10
8x10
9
6x10
9
4x10
9
•
Jcintra: improved
•
Jcinter: degraded
T = 64 K
unirradiated
21
irradiated 2x10 m
-2
21
irradiated 4.15x10 m
22
irradiated 1x10 m
0.01
-2
-2
0.1
1
µ0H (T)
LOW TEMPERATURE PHYSICS
Neutron irradiation effects on Jc for H parallel c:
Bruker HTS
LOW TEMPERATURE PHYSICS
Neutron irradiation effects on Jc anisotropy: AMSC
•
•
•
Reduced critical currents for fields
parallel a,b
Improved critical currents for fields
parallel c
At higher neutron fluence: second
peak
LOW TEMPERATURE PHYSICS
Summary: Critical Current Densities (JC)
H||a,b
H||c
"PF/CC coils"
"TF/CS coils"
"PF/CC coils"
10
JC (Am )
10
coils"
-2
-2
JC (Am )
10
10
µ0H||c
coated conductors
"TF/CS
77 K
64 K
BSCCOmultifilament tape
30 K
20 K
9
10
µ0H||ab
coated conductors
77 K
64 K
BSCCOmultifilament tape
50 K
40 K
8
10
0
1
2
3
4
5
8
10
6
7
8
9
µ0H (T)
•
•
9
10
10
11
12 13
14
15 16
0
1
2
3
4
5
6
7
8
9
10 11
12 13 14 15 16
µ0H (T)
The ellipses represent possible design requirements for fusion magnets (ITER
specification). A field of around 6 T is specified for the ITER PF coils and of around
13 T for the CS/TF coils.
The range of current densities between 108 Am-2 and 1010 Am-2 is highlighted.
LOW TEMPERATURE PHYSICS
The engineering critical current densities JE need to be improved!
2.1x10
8
9
2.1x10
-2
JE (Am )
10
-2
JC (Am )
10
10
7
µ0H||ab
µ0H||c
77 K
64 K
50 K
10
8
6
2.1x10
0.1
1
10
µ0H (T)
LOW TEMPERATURE PHYSICS
… but alternative materials exist … RE-123 (RE = Nd, Sm, Gd)
Higher Tc
→
Higher irreversibility fields at 77 K
Y-123
Nd-123
SmGd-123
94
93
Tc(K)
92
91
90
89
0
1
2
3
4
5
21
6
-2
fast neutron fluence (10 m )
7
8
M. Eisterer et al.: Adv. Cryog. Eng. 46, 655 (2000)
R. Fuger et al.: Physica C 470, 323 (2010)
LOW TEMPERATURE PHYSICS
… and new commercial cc’s, partly with artificial pinning centers
intrinsic pinning
correlated pinning
shoulders
LOW TEMPERATURE PHYSICS
… but we need
cables with highly demanding performance at high fields and temperatures
 high amperage (some 10 kA)
 long lengths
 high homogeneity
 low Jc anisotropy
 low ac losses
 high stress tolerance
e.g. Roebel cables or striated conductors
LOW TEMPERATURE PHYSICS
Homogeneity of cables or striated tapes (magnetoscan analysis)
• Homogeneity of the cable
• Identify damage of single strands
Striated tape
LOW TEMPERATURE PHYSICS
LOW TEMPERATURE PHYSICS
CONCLUSIONS
• Cc‘s are close to the field requirements of ITER / DEMO magnets at elevated
temperatures
• Neutron irradiation is beneficial as long as Tc is not too much depressed ()
• Neutron irradiation reduces the Jc anisotropy (may not be so important – AP’s!)
but
• Cable development is needed
• Y-substitution may be advisable
• Neutron irradiation to higher fluences is required
• Homogeneity issues must be carefully addressed
and
• all the other issues discussed at this conference must be solved!!
LOW TEMPERATURE PHYSICS
CO-WORKERS and COLLABORATIONS
CO-WORKERS at ATI
Michael Eisterer
René Fuger
Florian Hengstberger
Martin Zehetmayer
Johann Emhofer
Michal Chudy
COLLABORATIONS
SuperPower / University of Houston: V. Selvamanickam
American Superconductor: A. Malozemoff
Bruker HTS: A. Usoskin
Industrial Research: N. Long
Hypertech: M. Sumption
Sumitomo Electric Industries: K. Sato
FZ Karlsruhe: W. Goldacker
LOW TEMPERATURE PHYSICS