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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


• 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


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


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


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!


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


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)


YBa2Cu3O7- - Y-123


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)


H || c

H || a,b

Consequences for flux pinning


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


Experimental Jc data

8x1021m-2

1x1021m-2

(Am

-2)

F.M. Sauerzopf: PRB 57, 10959 (1998)


Connolly et al., TU-Delft 2000

Model defects in “2D” Bi-2223 tapes


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)


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


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)


• “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


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


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


“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)


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)


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)()(


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


Coated conductors

Focus on commercial tapes


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


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


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)


Neutron irradiation effects on Jc for H parallel c: Bruker HTS


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


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


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!


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)


… and new commercial cc’s, partly with artificial pinning centers

intrinsic pinning

correlated pinning

shoulders


… 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


Homogeneity of cables or striated tapes (magnetoscan analysis)

• Homogeneity of the cable• Identify damage of single strands

Striated tape


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!!


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

RADIATION EFFECTS ON HIGH TEMPERATURE SUPERCONDUCTORS › mumu › target › Weber ›...

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