General Overview of Superconducting General Overview of Superconducting MaterialsMaterials

P. KováčInstitute of Electrical Engineering of Slovak Academy of

Sciences, Bratislava, SlovakiaSuperconductivity in the IEE SAS:more than 40 years experienceTheory: pinning, field penetration, AC losses Superconducting compounds: Nb3Sn, Nb3Ge, YBCO, BSCCO and MgB2

Sup. magnets : modelling, winding tests, mag. prototypesTampere 4.11.2010

99 99 years of superconductivity years of superconductivity ...?...?

Superconducting story: KamerlinghOnnes in 1911 – first measurements to liquid helium

Hg - not formable into the wire- very low Tc , close to L He temp.

What has been found from that time?What about other superconducting elements, ..what applicable materials..?

Superconducting elementsSuperconducting elements

C. Buzea and T. Yamashita, Sup Sci Technology (2001) 14 R315

Today: 30 superconducting elements, max. Tc = 9K (Nb)

SuperconductingSuperconducting compoundscompounds

1900 1910 1920 1930 1940 1950 1960 1970 1980 1990 2000 20100

5

10

15

20

25

30

35

40

45

50

55

HTS materials

GdFeAsO1-δ

La2-xBaxCuO4

intermetallic compounds

alloyspure metals

MgB2

Low Tc superconductors

Nb3Ge

Nb3AlNb3SnVa3Si V3Ga

NbTi, NbZrNb

Pb

Hg

criti

cal t

empe

ratu

re [K

]

year of discovery

L He

L H2

L Ne

HighHigh temperaturetemperature superconductorssuperconductors

1985 1986 1987 1988 1989 1990 1991 1992 1993 19940

20

40

60

80

100

120

140 Hg2Ba2Ca2Cu3O8+yTl2Ba2Ca2Cu3O10

High Tc superconductors

2223

2212Bi-Sr-Ca-Cu-O - Meada

YBa2Cu3O7-x - Wu

La1,82Ba0.15CuO4 - Bednorz & Muller

criti

cal t

empe

ratu

re [K

]

year of discovery

77K

StructureStructure of of superconductingsuperconducting materialsmaterials

c

ab

Iron pniktides: structure similar to HTS materialsC. Buzea and T. Yamashita, Sup Sci Technology (2001) 14 R315

Crit

ical

Cur

rent

Den

sity

, A/m

m²

10

100

1,000

10,000

100,000

0 5 10 15 20 25 30Applied Field, T

YBCO75 K H||a-b

µbridge

Nb3Al DRHQ

NbTi APC

2212 round wire

YBCOH||c µbridge

2223tape B|_

At 4.2 K UnlessOtherwise Stated

1.8 KNb-Ti

PbSnMo 6S8

Nb3Sn Internal Sn

YBCO75 K H||c

1.8 KNb-Ti-Ta

MgB 2

filmNb3Sn

PITNb3Sn

1.8K

Nb3SnTape

Nb3Al RQHT+Cu

Nb3Al+Ge

NbTi +HT

NbTi multilayer

2223tape B||

Nb3SnITER

Critical current densities at 4.2 KCritical current densities at 4.2 K

D. Larbalestier, Univ. Wisconsin

SM for coil SM for coil application application -- compositescomposites::

Superconducting filaments in metallic matrix:

- High Tc, Jc and Bc2 of SF - Chemical compatibility with metallic sheath- Mechanical properties and thermal contractions of components- Formability of SM into ≈ μm size filaments- Sintering temperature and time (atmosphere, pressure ..)- High electrical and thermal conductivity of metallic components

(stability)

- High resistance to mechanical stresses (tension, bending, torsion-twisting)

- Low AC losses (for AC applications)

- Low conductor‘s price (raw materials, applied technology), …. …. decisive for applications

Available filamentary superconductors:Available filamentary superconductors:NbTi/Cu – Nb3Sn/Ta/Cu – BSCCO/Ag, .. // MgB2/Nb(Fe) ..Tc: 9K 18K 92 -105K 33- 39K

HT: 350oC/10h ≈700oC/100h 850-1000oC/100h 650-950oC/0.5hvacuum oxygen argon

1970 1975 1980 1985 1990 1995 2000 2005 2010102

103

104

20T

J c [A

/mm

2 ]

Year

NbTi Nb3Sn

4.2 K 5T

Matsumoto et al. Sup. Sci. Technol. 17 (2004) 989 HyperTech

Columbus

From: 1952 1987 2001Jc improvement of low Tc wires

PnictidePnictide wires by the ex situ PIT methodwires by the ex situ PIT method

Jc of SmFeAsO0.7F0.3−δ superconducting wireY Qi et al. Supercond. Sci. Technol. 23 (2010) 055009

High magnification SEM micrographs for low temp. annealing at 850 ◦C/35h

IEE of CAS HT conditions: - high temperatures ≈ 1200oC/50h- high pressure 1-6GPa

FilamentsFilaments micromicro--structurestructure

α-Ti

SmFeAsO0.8F0.2

Nb3Sn

NbTi

Pinning centres: GB,α-Ti prec., disl., defectscomp. to ξ

Bi-2223_surface

Bi-2223_textured

Weak-links, …texture..

MgB2

Porosity, connectivity,GB pinning, nano-sizedefects, ξ ≈ 5 nm

10nm

IIcc anisotropyanisotropy

2 4 6 8 10

1,0

1,5

2,0

2,5

3,0

3,5

4,0

4,5

ka = Ic-par / Ic-perp

1 filament composite tapes

anis

otro

py fa

ctor

, ka

tape's aspect ratio, b/a

MgB2, 4.2K, 8T Nb3Sn, 4.2K, 4T Bi-2223, 77K, 0.1T NbTi, 4,2K, 4T

Conductor flattening: - non uniform pinning (αTi, GB-Nb3Sn)- texture of Bi-2223 and MgB2 structure

P. Kováč: IEEE Trans. on Appl. Superconductivity, Vol. 16, No. 2, June 2006, 1453

B

B c-axis

Changed density of αTi : less dense in perp. dirr.

Advances of MgBAdvances of MgB2 2 compoundcompound

15- 20K, cooling by: H2 or cryo-cooler

• simple hex. structure• phase stability (temp. scale)• short sintering time• Tc above 20K, cooling costs• missing weak-links• C substitution of B:

Bc2 → 40-50T• 104Acm-2 at B >10T (4.2K)• low mass (space. appl.)• filamentary wires available• long length wires ≈1000 m• low price

CDoping by C:SiC, CNT, graphite, ...

Composition of MgB2 wires by PITMgB2 wires: by powder-in-tube process (PIT) :

powdered filaments deformed in a metallic sheath

Powders: MgB2 – ex-situ: particles 0.1-60µm, Mg-B – in-situ: particles 1-20µm Mg-B+MgB2 – mech. alloyed: particles 5-20nm

Powder flow – particle size (morphology) and hardness (friction) dependent

Metals: Fe, Ni, SS, Cu, Monel, Glidecop, Nb, Ta, Ti, NbTi- different plasticity, σ(ε) , work hardening (wh), annealing for wh recovery, ..

Composition: filaments // barrier // stabilization // mechanical supportBarrier: chemically inert: Nb, Ti, NbTi and Ta Stabilization: OFHC, GlidecopMechanical reinforcement: CuNi, Monel, SS and Glidecop

Transport Jc of 4-fil. rolled MgB2 wires

2 3 4 5 6 7 8 9 10 11 12102

103

104

105

HyperTech, USA

5T 6,5T

7,5T 11,3T10,3T

4 fil. wires

T = 4.2K

criti

cal c

urre

nt d

ensi

ty [A

cm-2]

magnetic field [T]

4 3 5, SiC 5, C 1 2 H.Tech

P. P. KovKovááčč et al., et al., Sup. Sup. Sci.TechnolSci.Technol 22 22 (2009) 075026(2009) 075026

EE II E/IE/I II MAMARWIT techniqueRWIT technique

TAR

2002

2009

Cold drawn SS reinforced MgB2 wiresNbTiNbTi barrier barrier Ti barrierTi barrier

3 4 5 6 7 8 9 10 11103

104

105

0.86mm, 800oC/0.5h

criti

cal c

urre

nt d

ensi

ty [A

cm-2]

magnetic field [T]

4.2 K 20 K

3 4 5 6 7 8 9 10104

105

1-086

criti

cal c

urre

nt d

ensi

ty [A

cm-2]

magnetic field [T]

650oC 750oC 850oC

P. Kováč et al., Sup. Sci. and Technology 23 (2010) 025014,.. 23 (2010) 65010

MgB2/Ti/Cu/SS wire, filament size

0 50 100 150 200 250103

104

105

criti

cal c

urre

nt d

ensi

ty [A

/cm

2 ]

filament size [μm]

19 fil. Ti/Cu/SS [..] 19-361 fil. Ni/Monel [..] 7 fil. NbTi/Cu/SS [..] 18-54 fil. Ti/Cu/Monel [..] 6-24 fil. Cu/Fe [..]

5,5T, 4.2 K

10 x

0,2 0,4 0,6 0,810-1

100

101

102

20 40 60

2x104

4x104

6x104

8x104105

J c [A/

cm2 ]

filament size [μm]

filam

ent s

ize

[μm

], I c(5

,5T)

[A]

wire diameter [mm]

filament size Ic (5,5T)

5,5T, 4.2K

16.616.6μμm fm filaments ilaments –– record!record!

Drawn down to 0.25 mm

P. Kováč et al., Sup. Sci. and Technology 23 (2010) 10506

Degradation of MgB2/ NbTi(Ti)/Cu/SS

0,0 0,2 0,4 0,6 0,8 1,00,0

0,2

0,4

0,6

0,8

1,0

1,2

0

200

400

600

800

1000

1200

600oC/2,5h800oC/0,5h

nor

mal

ized

crit

ical

cur

rent

ε [%]

σ [M

Pa]

The highest The highest εεirrirr

HyperTechHyperTech

Kováč P et al., Sup. Sci. and Technol. 23 (2010) 025014 / 065010

σ(ε) and Ic (ε) char. At 4.2K:

Twisting of 19-filament wire

4 5 6 7 8 9 101

10

100

0 10 20 30 40 50 600,6

0,7

0,8

0,9

1,0

norm

. Ic

Lt / d

4 T 10 T

criti

cal c

urre

nt [A

]

magnetic field [T]

2,50 mm 2,77 mm 3,12 mm 3,57 mm 4,16 mm 5,55 mm 7,14 mm 16,66 mm 25,00 mm

0 10 20 30 40 50 60 70 80 90 100 1100,4

0,5

0,6

0,7

0,8

0,9

1,0

1,1

no

rmal

ized

crit

ical

cur

rent

Lt / d

19 fil. Ti/Cu/SS 12 fil. Nb/Cu/CuNi [8] 4 fil. Nb/AgMg [7] 4 fil. Fe [7]

5T, 4,2K

The best resistance to twisting!The best resistance to twisting!

High resistance to torsion stress (twisting) and no High resistance to torsion stress (twisting) and no IIcc degradation for degradation for LLtt//dd > 30.> 30.

MgB2 cables, round or flat strands

C7

CTC6

W7 C7 C49

C49

MgBMgB22/Ti/Cu/Monel/Ti/Cu/Monel MgBMgB22/Ti/Cu/Ti/Cu MgBMgB22/NbTi/Cu/SS/NbTi/Cu/SS

0.335 mm0.335 mm 0.38 mm0.38 mm1.18 mm1.18 mm

0 .335 x 0.9 mm0 .335 x 0.9 mm22, , filament 135 x 390 filament 135 x 390 μμmm22

≈≈ 100 100 μμmm ≈≈ 120 120 μμmm ≈≈ 30 30 μμmmfilament size:filament size:

LLtt = 13 mm= 13 mm

LLtt = 15 mm= 15 mm

LLtt = 15 mm= 15 mm

Continually transposed conductor (CTC)Continually transposed conductor (CTC)

Current densities of MgB2 cables

Ic – critical current at 1μVcm-1

Jc – filament current densityIc/filaments area

Je – engineering current densityIc/conductor area

Jw – window current densityIc/window area

3 4 5 6 7 8 9

103

104

win

dow

cur

rent

den

sity

[Acm

-2]

magnetic field [T]

W7 C7 CTC6 C49

3 4 5 6 7 8 9

103

104

engi

nner

ing

curr

ent d

ensi

ty [A

cm-2]

magnetic field [T]

W7 C7 CTC6 C49

3 4 5 6 7 8 9104

105

filam

ent c

urre

nt d

ensi

ty [A

cm-2]

magnetic field [T]

W7 C7 CTC6 C49

JJcc

JJee

JJww

Hušek I et al., Cryogenics 2009 49 366

MgB2 thin films ⇔ wires …?A. Matsumoto et al., IEEE TRANS APPL SUP., 19, JUNE 2009

PIT tape with MA powderW. Haessler et all. Sup. Sci. Technol. 2008 21 06201

PIT MgB2 wires: - improved connectivity – reduced porosity andsecondary phases ( < 15 % now) - fine filamentary < 50 μm

Conclusion• After 99 years, only few superconducting materials applicable for

superconducting magnets are available• Filamentary superconductors in ≈ km lengths: NbTi, Nb3Sn, Bi-2212,

Bi-2223, a MgB2• NbTi and Nb3Sn – mostly used, still improved (after 55 years)• MgB2 – under development (9 years, MRI already existing)• Y-123 – high Jc thin films, (23 years), no filaments, lengths & price.???• Iron pnictides – int. studied (3 years), not promising for filam. wiresDecisive matters for future application of SM:• Conductor price – 1- 250 €/kAm• Cooling price: He, cryocoolers, H2, Ne, ... • Trends in energy: power density, energy generation (wind,

fusion…), widely used liquid H2, ...