SOWIT, Rome, 24.10.2011 1

Improvement of Industrial wires: MgB2 and HTS conductors

René Flükiger

Dept. Applied Physics (GAP)University of Geneva, Switzerland

Now: CERN Associate

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Outlook

* Overview: recent progress on various conductor typesfor possible application in wind mill generators

* Y or R.E. based coated conductors* Conductors produced by P/M techniques: - Bi-2223, Bi-2212 (very brief) - MgB2 wires

* Problems to be solved* Conclusions

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Systems to be used at T = 77 K

R.E.BaCuO tapes

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Current density * Carry optimized current in REBaCuO (dopants)

Mechanical * Substrate strong enough at high temperature to stand the formation of REBaCuO * Tape as a whole strong and flexible enough to be wound into cable and coils at 300 K * Tape must withstand longitudinal and transverse stresses during operation

Electrical stability * Carry excess current in Ag layer and in in Al, Cu,……. outer layers

Thermal stability * Enable heat transfer to the coolant

AC losses * Modify architecture to minimize AC losses (Roebel, striations)

Requirements to a REBaCuO tape

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Many ways lead to REBaCuO coated conductor tapes

Coating with liquid (metal organic deposition) MOD (AMSC)

Adsorb vapors (metal organic chemical vapor deposition, MOCVD (SuperPower)

Adsorb metal atoms from vacuum (pulsed laser deposition), PLD (Bruker, SEI) (electron beam evaporation):RCE (SuNAM)

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D. Hazelton et al., ASC 2010

REBaCUO tape of SuperPower

2G wire based on IBAD MgO and MOCVD process

< 0.1 mm

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SEI: Fabrication width 30 mm, No indication about production rate

AMSC: Fabrication width 40 mm, Goal: 100 mm width, lengths: > 500 m> 1’000 km/year of 4 mm tape

SuperPower: Fabrication width 12 mm, Lengths: 1’400 mJuly 2010: > 150 km/year (?)

Fujikura: Fabrication width 10 mm, lengths: > 1’000 m2009: PLD/CeO2 (60 m/h), IBAD MgO (≤1,000 m/h), Y2O3 (500m/h),Al2O3 (150 m/h), GdBaCuO (15 m/h)

SuNAM: Fabrication width 12 mm, lengths: > 100 m (planned: 2’000 m)Nov. 2009: Homoepitactic (70m/h),LMO buffer (50 m/h)Goal: 2,000 km/year (assuming 100% yield)

Bruker: Fabrication width 40 mm, lengths: ≤ 100 m (planned: > 1’000 m) Goal: line speed (ABAD) 30 m/h and PLD (70 m/h)

Summary: Fabrication width, production rate

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What remains to be done ?

*Higher Jc values:

- higher homogeneity over whole length- thicker layers- enhanced pinning by nano-additives- reduced anisotropy by nano-additives

* Reduced ac losses

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Higher critical current density

Enhanced layer thickness

M. Igarishi et al., EUCAS 2009 (Fujikura)

Fujikura reports 6 mm thick layer with 1’040 A/cm-w

(Deposition time not reported)

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2008: BaZrO3 was demonstrated in MOCVD o achieve dramatic in-field performance improvements

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SuperPower, 77K/1T

V. Selvamanickam and J. Deckow, DOE Peer Review 2010

AMSC, 77K, 1 T

M. Rupich, J. McCall, C. Thieme, DOE Peer Review, 2010

Higher critical current densityEnhancement of Jc for fields out-of plane: the minimum Jc is the decisive one for applicationsFurther progress still to expect

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Effect of tensile stress on Jc

Flükiger, Les Diablerets, 29.6.-1.7.2011

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16

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Systems to be used at T ≤ 40 K

Use of cryorefrigerators

Bi- based systems: Bi-2223, Bi-2212 (?)

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The system Bi-2223

Data from K.I. Sato, Sumitomo

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The system Bi-2212

Recent results of D. Larbalestier et al. (Tallahassee):

Application of cold isostatic pressure on Bi-2212 wires

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New data of D. Larbalestier (Peter Lee plot)

⊥

//

Jc doubled after CIP treatment

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Disadvantages of Bi based systems:

* In presence of fields above 0.5 T only operational at T ≤ 30K* Costs of Ag will always be an obstacle (in particular with the future tendency of material costs) * Low mechanical strength (tensile and compressive)

Advantages of Bi based systems:

* High thermal stability

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The system MgB2

Large scale applications:

* LINK (CERN)

* Poloidal field coils ?

* Ignitor ?

Use of cryorefrigerators at T ≤ 20K

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Preparation of MgB2 wires by 3 different P/M techniques

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Comparison between ex situ and in situ binary MgB2 wires

Available literature values for round wires; tapes have higher Jc values

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MID process (Japan)

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Advantages of ex situ technique

* Longer lengths produced (> 2 km)* Higher homogeneity over whole lengths

Advantage of in situ technique

* Possibility of doping (higher values at high fields)

MgB2 wires:much ligh than every other s.c. wires

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Densification of Multifilamentary MgB2 wires

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Drawn to a square cross section After cold densification 1.0 mm 1.0 mm

Binary Fe/MgB2 wire

Densification pressures for MgB2 wires: 1 – 1.5 GPa

R. Flükiger, M.S.A. Hossain, C. Senatore, SuST 22(2009)095004

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Mechanism of densification effects in MgB2 wires

MgB2 is a forgiving material: No cracks at limit between unpressed and pressed filament

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Monofilamentary MgB2 wires with malic acid additives

Highest values known so far for in situ MgB2 wires

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Sheath

Material

P

(GPa)

Wire cross

section

(mm x mm)

Filament

cross

Section

(mm2)

Fill

factor

(%)

Mass

Density

(Mg+2B)

(g/cm3)

Relative

mass

density

(%)

Vickers

micro-

hardness

(GPa)

Monel/Nb/Cu 0 0.61 x 1.00 0.0957 15.5 1.015 51 1.4

Monel/Nb/Cu 1.5 x 1.01 0.0829 14.3 1.413 69 3.6

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Homogeneous areal change of all densified filaments

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4.2 K

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The exponential n factor: strong enhancement

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Densification of long MgB2 wire lengths

Two independent hydraulic systems: 40t/16tControl of the 4 anvils: * independent pressure set

* independent time of pressureVery high exerted pressures: 1 – 1.5 GPa

(several times higher than an extrusion machine)Pressure sequence: 2.3 sTraveling distance between pressing steps: 14 mmPressing length: 70 mmTotal densified length (estimated): 300 m/day

Densified lengths of 1 km / day: possible after modifications

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* Jc of in situ wires: enhanced by a factor 2.3* There is still a potential for improvement of Jc. * Costs a factor 50 to > 100 lower than for HTS superconductors

4 8 12 16 20 24 28

103

104

105

106

//

//

Matsumoto / Thin Film Hässler / Tape Hossain / Rectangular wire Togano / IMD wire

J c [A

/cm2 ]

B [T]

//

Nb3Sn

4.2 K

Conclusions: MgB2

* To improve: thermal stabilization

Densification: applicable on any P/M system:*Bi-2212 (under work)*Future s.c. systems

At B < 3 T (generators):Differences become much smaller between various techniques

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Reduction of AC losses

* Roebel technique,* Striations,* Roebel + striations