LOW TEMPERATURE PHYSICS
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
• 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?
From ITER to DEMO
HTS Magnets ?
YBCO, BiSCCO, MgB2
ITER DEMO
LOW TEMPERATURE PHYSICS
Options / Materials
“Demo” design (magnetic field, temperature, fluence)
• Cheaper: MgB2
• Higher fields: HTSBi-2212: ≤ 10 KBi-2223: ≤ 20 KCoated conductors (RE-123): ≤ 50 K
• Higher temperatures:Coated conductors (RE-123) ~ 65 -77 K
LOW TEMPERATURE PHYSICS
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)
NEUTRON SPECTRA
LOW TEMPERATURE PHYSICS
LOW TEMPERATURE PHYSICS
DAMAGE ENERGY SCALING
(E) neutron cross sectionT(E) primary recoil energy distributionF(E) neutron flux density distributiont 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
FAST NEUTRONS (E>0.1 MeV)
COLLISION CASCADES,IF THE ENERGY OF THE
PRIMARY KNOCK-ON ATOM EXCEEDS 1 keV
STATISTICALLY DISTRIBUTED
~ SPHERICAL, ~ 2.5 nm Ø
SURROUNDED BY A STRAIN FIELD OF THE SAME SIZE
5 x 1022 defects m-3 per 1022 neutrons m-2
Neutron-induced Defects in HTS
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
0 2 4 6 8 10 12 14 16 18 20 22
87
88
89
90
91
92
trans
ition
tem
pera
ture
(K)
fast neutron fluence (1021 m-2)
F.M. Sauerzopf: PRB 57, 10959 (1998)M. Eisterer et al.: Adv. Cryog. Eng. 46, 655 (2000)
LOW TEMPERATURE PHYSICS
H || c
H || a,b
Consequences for flux pinning
LOW TEMPERATURE PHYSICS
M. Kraus et al.: Phys. Bl. 50, 333 (1994)
The same defects act differently in different materials
Example: parallel columnar defectsc-axis
Y-123 (“3D”): Peak for H parallel to columns
Bi-2212 (“2D”): Reduction of Jc anisotropy
LOW TEMPERATURE PHYSICS
Experimental Jc data
8x1021m-2
1x1021m-2
(Am
-2)
F.M. Sauerzopf: PRB 57, 10959 (1998)
LOW TEMPERATURE PHYSICS
Connolly et al., TU-Delft 2000
Model defects in “2D” Bi-2223 tapes
LOW TEMPERATURE PHYSICS
0 1 2 3 4 5 6105
106
107
108
18.580
J c (A
/m2 )
µ0H (T)
unirr. 3*1019m-2
HIIab
HIIc
Critical Currents at 77 K
S. Tönies et al.: IEEE Trans. Appl. Supercond. 11, 3904 (2001)
LOW TEMPERATURE PHYSICS
40 50 60 70 80 90 100
0
1
2
3
4
5
6H||ab
unirr.
6*1018m-2
1.2*1019m-2
2*1019m-2
3*1019m-2
5.5*1019m-2
H||c
unirradiated
6*1018m-2
1.2*1019m-2
2*1019m-2
3*1019m-2
5.5*1019m-2
µ 0H(T
)
T(K)
Irreversibility Lines
LOW TEMPERATURE PHYSICS
0 2 4 6 8 10 12 14
108
109
1010
Fission Tracks
77 K
70 K
60 K
50 K
30 K
5 K
J c(Am
-2)
B (T)0 2 4 6 8 10 12 14
Collision Cascades
Y-123: Similar behavior of fission tracks and collision cascades
M. Eisterer et al.: SUST 11, 1001 (1998)
LOW TEMPERATURE PHYSICS
• “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 pancakesReduced intrinsic pinning through disorder (H || a,b)
SUMMARY: NEUTRON - INDUCED DEFECTS
LOW TEMPERATURE PHYSICS
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 RE-123 coated (2G) conductorsITER 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
PRACTICAL MATERIALS
4 HTS compounds suitable for fusion applications
Magnetic field applications at T > 50 K only with RE-123 HTS compounds
LOW TEMPERATURE PHYSICS
Pure MgB2 is anisotropic: = Hc2ab/Hc2
c ~ 5
Grains are randomly oriented:
different upper critical fields in different grains!
Distribution function:
3 4 5 6 7 8 9 10 11 12 13 140.00
0.05
0.10
0.15
0.20
0.25
0.30
0.35
0.40
Bc2||Bc2
rela
tive
abun
danc
e
Bc2(T) M. Eisterer et al.: JAP 98, 033960 (2003)
MgB2 Wires
LOW TEMPERATURE PHYSICS
“Irreversibility line” can be shifted by an increase of Bc2 and / or by a reduction of the anisotropy:
Neutron irradiation increases Bc2 and decreases .
abc
c
Bp
B 222011
1
0 5 10 15 20 25 30 35 400
2
4
6
8
10
12
14
B (T
)
T (K)
undamaged irradiated Bc2
B=0
M. Eisterer et al.: JAP 98, 033960 (2003)
LOW TEMPERATURE PHYSICS
Neutron irradiation:
Bc2 ↑ B=0 ↑ Jc(B) ↑ at high magnetic fields
0 2 4 6 8 10
107
108
109 unirradiated 2x1022 m-2
Ic (A)
J c (Am
-2)
0H (T)
10
100
1000
Cu-sheathed wire
Introduction of defect cascades is less important, grain boundary pinning is dominant !
M. Eisterer et al.: SUST 15, 1088 (2002)
LOW TEMPERATURE PHYSICS
0 2 4 6 8 10 12 14 16 18104
105
106
107
108
109
J c(A
/m2 )
unirr. irr. bulk (5 K) wire (4.2 K)
B(T)
Critical currents can be fully explained by a percolation model (solid lines)
M. Eisterer et al.: Phys. Rev. Lett. 90, 247002 (2003)
dJp
pJpBJc
cc
79.1
1)()(
LOW TEMPERATURE PHYSICS
0 5 10 15 20 25 30 35 40105
106
107
108
109
1010
1011
Bc2=40 T, =4.3
Bc2=55 T, =3.2
J c(Am
-2)
B(T)
Bc2=74 T, =1.85
EXTRAPOLATED PERFORMANCE at 4.2 K
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
50 55 60 65 70 75 80 85 90 95 100 105 1100
2
4
6
8
10
12
14
16 coated conductorsµ0H||ab µ0H||c
BSCCO multifilament tapeµ0H||ab µ0H||c
64 K
µ 0H (T
)
T (K)
77 K
77 K H||c
AMSC 5.6 T
Bruker 7.7 T
Sumitomo 1.15 T
LOW TEMPERATURE PHYSICS
Neutron irradiation
• Jcintra: improved
• Jcinter: degraded
0.01 0.1 1
4x109
6x109
8x109
1010
2x1010
4x1010
T = 64 K unirradiated
irradiated 2x1021 m-2
irradiated 4.15x1021 m-2
irradiated 1x1022 m-2
J c (A
m-2)
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)
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16
108
109
1010
"TF/CS coils"
µ0H||abcoated conductors
77 K 64 K
BSCCOmultifilament tape 50 K 40 K
J C (A
m-2)
µ0H (T)
"PF/CC coils"
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16
108
109
1010
µ0H||ccoated conductors
77 K 64 K
BSCCOmultifilament tape 30 K 20 K
J C (A
m-2)
µ0H (T)
"TF/CS coils""PF/CC coils"
• 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.
H||a,b H||c
LOW TEMPERATURE PHYSICS
0.1 1 10108
109
1010
2.1x106
2.1x107
2.1x108
µ0H||ab µ0H||c 77 K 64 K
50 K
J E (Am
-2)
J C (A
m-2)
µ0H (T)
The engineering critical current densities JE need to be improved!
LOW TEMPERATURE PHYSICS
0 1 2 3 4 5 6 7 889
90
91
92
93
94 Y-123 Nd-123
SmGd-123
T c(K)
fast neutron fluence (1021 m-2)
… but alternative materials exist … RE-123 (RE = Nd, Sm, Gd)
Higher Tc → Higher irreversibility fields at 77 K
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 ATIMichael EistererRené FugerFlorian HengstbergerMartin ZehetmayerJohann EmhoferMichal Chudy
COLLABORATIONS
SuperPower / University of Houston: V. SelvamanickamAmerican Superconductor: A. MalozemoffBruker HTS: A. UsoskinIndustrial Research: N. LongHypertech: M. SumptionSumitomo Electric Industries: K. Sato FZ Karlsruhe: W. Goldacker