MgB2 wire performance

Giovanni GrassoMay 20th, 2008

CoworkersCoworkers BASIC R&D

CNR-INFM: A. Malagoli, V. Braccini, C. Bernini, C. Fanciulli, M. Tropeano, M. Vignolo, C. Ferdeghini, M. Putti

CONDUCTOR DEVELOPMENTColumbus Superconductors: S. Brisigotti, A. Tumino, D. Pietranera, E. Demencik, S. Berta, R. Penco

POWDERS DEVELOPMENTFerrania Technologies: S. Magnanelli, A. Gunnella

MAGNET DEVELOPMENTASG Superconductors: R. Marabotto, M. Modica, D. Damiani, D. Nardelli

MgB2: this new material represents the natural evolution for applied superconductivity of today and tomorrow

Superconductivity in MgB2 was publicly announced in January 2001 by Japanese scientists

From then on MgB2 represents the known binary material showing superconductivity at the highest temperatures to date

As virtually all superconductors used in large-scale industrial applications are binary materials (NbTi, Nb3Sn), it appeared immediately evident that MgB2 might have represented a new option

So far researchers worldwide produced literally hundreds of scientific manuscripts focused on this surprising discovery

Helium (liquid) is a natural resource available in limited quantities and it represents a bottleneck to industrial developments using superconductivity : MgB2 is a convenient solution to that

Preamble

Important parameters for industrial applications

Material Tc Hc2 ( T= 4.2 K) ξ (nm)Mass

Density

Nb-Ti 9 K 10 T 5 6.0 g/cm3

Nb3Sn 18 K 28 T 5 7.8 g/cm3

MgB2 39 K 60 T 5 2.5 g/cm3

YBCO 90 K > 50 T << 1 c 5.4 g/cm3

BSCCO 110 K > 50 T << 1 c 6.3 g/cm3

World market

MgB2 is an HTS with

properties and price

more near to an LTS

The questions are: how much of the current and future LTS and HTS market MgB2 will grab?and how big will the new market generated by MgB2 be?

  C

riti

cal

Cu

rren

t D

ensi

ty,

A/m

m² 

 

10

100

1,000

10,000

100,000

0 5 10 15 20 25 30Applied Field, T

Nb-Ti: Max @4.2 K for whole LHC NbTistrand production (CERN-T. Boutboul)

Nb-Ti: Max @1.9 K for whole LHC NbTistrand production (CERN, Boutboul)

Nb-Ti: Nb-47wt%Ti, 1.8 K, Lee, Naus andLarbalestier UW-ASC'96

Nb-37Ti-22Ta, 2.05 K, 50 hr, Lazarev et al.(Kharkov), CCSW '94.

Nb3Sn: Non-Cu Jc Internal Sn OI-ST RRP1.3 mm, ASC'02/ICMC'03

Nb3Sn: Bronze route int. stab. -VAC-HP,non-(Cu+Ta) Jc, Thoener et al., Erice '96.

Nb3Sn: 1.8 K Non-Cu Jc Internal Sn OI-STRRP 1.3 mm, ASC'02/ICMC'03

Nb3Al: JAERI strand for ITER TF coil

Nb3Al: RQHT+2 At.% Cu, 0.4m/s (Iijima et al2002)

Bi-2212: non-Ag Jc, 427 fil. round wire,Ag/SC=3 (Hasegawa ASC-2000/MT17-2001)

Bi 2223: Rolled 85 Fil. Tape (AmSC) B||,UW'6/96

Bi 2223: Rolled 85 Fil. Tape (AmSC) B|_,UW'6/96

YBCO: /Ni/YSZ ~1 µm thick microbridge,H||c 4 K, Foltyn et al. (LANL) '96

YBCO: /Ni/YSZ ~1 µm thick microbridge,H||ab 75 K, Foltyn et al. (LANL) '96

MgB2: 4.2 K "high oxygen" film 2, Eom etal. (UW) Nature 31 May '02

MgB2: Tape - Columbus (Grasso) MEM'06

2212round wire

2223tape B|_

At 4.2 K UnlessOtherwise Stated

1.8 KNb-Ti

Nb3SnInternal Sn

2 KNb-Ti-Ta

Nb3Sn1.8 K

NbTi +HT

2223tape B||

Nb3SnITER

Nb3Al: ITERMgB2

film

YBCO µ-bridge

H||c

YBCO µ-bridge

H||ab 75 K

MgB2

tape

Nb3Al:

RQHT

Critical currents of technical superconductors at 4.2 K

Superconductors choice is ‘in principle’ quite wide,but jc is not the only important parameter for selection

Low costLow cost

HandlingHandling

SC joints,AC losses,n-factor,etc.

SC joints,AC losses,n-factor,etc.

PerformanceB,TPerformanceB,T

Little investmentfor end-usersto test it on theirproducts

Little investmentfor end-usersto test it on theirproducts

MgB2

superconductor

Driving forces for MgB2

• Low cost and wide Low cost and wide availability of the raw availability of the raw materials, particularly in materials, particularly in EuropeEurope

• Excellent chemical and Excellent chemical and mechanical compatibility mechanical compatibility with various elements (Ni, with various elements (Ni, Fe, Ti, Nb, Ta, Cr, although Fe, Ti, Nb, Ta, Cr, although not with Cu)not with Cu)

• Potential for very good Potential for very good performance at high fields performance at high fields ( thin films show H( thin films show Hc2c2 > 60 T > 60 T ! )! )

• Low anisotropy and Low anisotropy and potential for persistent potential for persistent mode operation (high n-mode operation (high n-value, low current decay value, low current decay at medium magnetic at medium magnetic fields)fields)

About our today’s structure

The new plant is ready and operational for a wire production scalable up to 3’000 Km/yearWire unit length up to 5 Km single piecesTotal plant area 3’400 m2 – 50% only used today

R&D

Powderproduction

7 engineers7 workers2 consultantsIndirect activities to ASG

3 employees

2 professors3 senior researchers4 Postdocs2 PhD students

Columbus Superconductors activities involve about 30 people

Fabrication of MgB2 wires by the ex-situ P.I.T. method used

+

B Mg MgB2amorphous

95-97% purity

325 mesh99% purity

mixing

tube filling1.3 g/cm3

reaction at900°C in Ar

wire drawing to 2 mm cold rolling reaction at900-1000°C in Ar

Straightforward multifilament processing Significant homogeneity over long lengths Allows careful control of the MgB2 particle size and purity

Need of hard sheath materials and strong cold working Jc is very sensitive to the processing route More tricky to add doping and nanoparticles effectively

Reliable method for exploring long lengths manufacturing

advantagesadvantages

disadvantagesdisadvantages

Fabrication of MgB2 wires by the ex-situ P.I.T. method

MicrostructureMicrostructure

Transverse cross section area:

• MgB2 0.21 mm2 (total area)• Cu 0.35 mm2

• Fe 0.19 mm2

• Ni 1.54 mm2

Composite wire:

99.5% pure Nickel matrix

14 MgB2 filaments

OFHC 10100 Copper core

99.5% pure Iron barrier

Dimension 3.6 mm x 0.65 mm ( w x t )

Standard batch length: > 1700 m

Cu Fe NiMgB2

Constant improvement of conductors Constant improvement of conductors from production: Ifrom production: Icc at 20K of 1.7 at 20K of 1.7

Km tapesKm tapes

20K

1.2T

1.4T

1.6T

1000 1005 1010 1015 1020 1025 1030

10

20

30

40

50

60

70

80

n -factor at 1.4T and 16K, 20K, 24K

16K

20K

24K

1.4 Tn-

fac

tor

Conductor #

Ic at 20K, 1 T always >> 90 An-factor at 20K, 1 Tesla >> 30Minimum bending diameter: 65 mmMaximum tensile strain: 150 MPa

A total of 50 lengths of 1.7 Km each have been successfully produced and tested until Nov. 2006

They have been used for two Open MRI systems

Optimisation of the wires fabrication by varying sheaths, Optimisation of the wires fabrication by varying sheaths, geometry of the conductor,…geometry of the conductor,…

Wire B37 filamCu stab

Monel

Cu

Wire C19 filamno Cuup to 61

Ni

Going from flat tape to round-square wires cleans up conductor anisotropy, and the field dependence of Ic improves accordingly

P.I.T. e-situ methodP.I.T. e-situ method+

BB MgMg MgBMgB22

B2O3

Home made boron

MgB2+

B Mg

+B Mg MgB2

Commercial precursors

Commercial MgB2

Possible routes: Possible routes:

High High energenergy ball y ball millinmillin

gg

B

Doped boronMgB2(doped)

+

dopant

+B(doped) Mg

tube filling wire drawing to 2 mm cold rollingreaction at

900-1000°C in Ar

Progress in the Ic of the flat tape conductor in multi Km-length

Time Process 20K, 1 Tesla 20K, 2 Tesla

2006 Standard, 8.5 % filling factor 200 65

Beginning 2007 Improved cold working 250 75

End 2007 Controlled atmosphere 330 80

Today Increased filling factor to 10.5% 390 95

Mid 2008 Improved MgB2 reaction path 500 150

End 2008 MgB2 ball milling and doping >> 500 >250

3.6 x 0,65 mm

2.3 mm2

With Monel sheath minimum bending radius 30 mm

MgB2 grains are covered by 5 nm of MgO layer within 2 hours of exposition of powders to air ( this layer has a thickness ~ ξ )

Working in Oxygen-cleaner conditions is mandatory!

Critical current improvement followed by inert-atmosphere handling

Ic is improved by a factor larger than 2 at virtually all fields just by inert atmosphere powder handling during the entire process

10000 20000 30000 40000 50000

10000

100000

1000000

Jc (

A/c

m2

)

B (Gauss)

CG152a T=730°C CG148a T=745°C CG125a T=752°C CG127a T=760°C CG126a T=768°C CG155a T=737°C

MgB2 powder synthesis temperature

Wires T=5K

730 740 750 760 770 7800

20000

40000

60000

Fili

Jc (

A/c

m2

)

T set (°C)

Jc vS T @ 5K-4,5T

SQUID

1.0E+03

1.0E+04

1.0E+05

1.0E+06

0 1 2 3 4 5

Magnetic Field (T)

Mag

net

ic J

c [A

/ cm

2 ] Jc@5K

1.0E+03

1.0E+04

1.0E+05

1.0E+06

0 1 2 3 4 5Magnetic Field (T)

Mag

net

ic J

c [A

/ cm

2 ] Jc@5K

0.0

0.2

0.4

0.6

0.8

1.0

1.2

0 0.2 0.4 0.6 0.8 1H / Hk

Fp

/ F

p m

ax

Effect of synthesis temperature

Decreasing synthesistemperature

Point Defect Pinning

Grain Boundaries Pinning

Decreasing synthesistemperature

Not controlled atmosphere Glove box

0

0.2

0.4

0.6

0.8

1

1.2

0 0.2 0.4 0.6 0.8 1H/Hk

Fp

/Fp

ma

x 5K 5K

The effect of high energy ball milling is evidentTo increase the milling time (up to a certain value) – the tightness of the jars needs to be improved on longer times

-1x106 0 1x106 2x106 3x106 4x106 5x106 6x106 7x106 8x106 9x106 1x107

0

5000

10000

15000

20000

25000

30000

35000

36x360

0x0

72x360

72x300

72x240

36x300

36x240

Jc (

A/c

m^

2)

rpm^2 x h

B=4.5TT=5K

Giara da 500ml in SSBPR=8.4

new

Milling

0.0 2.0x106 4.0x106 6.0x106 8.0x106 1.0x107

0

1x104

2x104

3x104

4x104

5x104

6x104

7x104

13

12

1110

9

87

6

5

43

2

1

1=(0x0)2=(180x5)3=(180x24)4=(300x15)5=(240x36)6=(180x72)7=(300x36)8=(240x72)9=(180x144)10=(300x72)11=(180x256)12=(360x72)13=(360x36)Jc

(A

/cm

^2)

rpm^2 x t

B=4 T T=5 K

Milling

0 10000 20000 30000 40000 50000102

103

104

105

106

Jc (

A/c

m^2

)

B (Gauss)

180x144 BPR 14 300x36 BPR 8.4 300x36 BPR 17

50g MgB2

Milled with different BPR

Carbon additions can be also introduced during ball milling. Because it does not enter MgB2 in a very uniform way by such a process, it is benificial if it is added to a very low levels.

Doping with ex-situ is underway

Doping with nanosized SiC is effective provided that it is added to the Boron powders prior to MgB2 synthesis

Further improvement is expected while SiC is added to optimized milling process

Control of powder production Control of powder production process is crucial to achieve process is crucial to achieve

optimal particle sizeoptimal particle size

1000 nm1000 nm

450 nm450 nm

30 μm30 μm30 μm

CommercialMgB2 MgB2 from

commercial Boron

MgB2 from own Boron

T = 20 K

SQUID measurements

What is necessary to do to meet current wire demands?

Some applications do not need better powders than today’s production (dedicated low-field MRI, FCL, CERN), only more engineered conductors are preferrable – strong activity is ongoing to reach targets over long lengths

Fully non-magnetic, high resistive matrix, twisted, for low-AC loss applications

What is necessary to do to meet current wire demands?

Most of the applications do need better powders than today’s production in very large quantities, as well as more engineered conductors are preferrable – the last point has been already addressed – wires are twisted with no degradation, and electrically insulated with different techniques as braiding, wrapping, etc.

All wires produced in Km-class length with no degradation

• Boron• Magnesium• Other metals and alloys constituents of the wire

Compound Typical batch of today (x Kg)

Amorphous Boron (97%) 250 €

Magnesium source (-325 mesh) 100 €

Pure Nickel 80 €

Pure Iron 1 €

Cu OFHC 10 €

SS 304 4 €

Materials cost estimate

In a wire we have:

60% Ni

15% Cu

15% MgB2

10% Fe

Materials cost target for large production volumes:

below 1 €/m

MgB2 wire technologies

• The production of long length of MgB2 wires has been demonstrated in the past years, with supply to ASG and other customers of about 150 Km of conductor

• In 2008 the wire production will be of about 200-300 Km, although our production capability, considering some additional limited investment, can be raised to >1’000 Km/year in 3-6 months time in the present production plant

• Survey of different technologies to produce wires (in-situ, ex-situ), and different ways to produce and improve B and MgB2 powders is always active

• Most of today’s effort is concentrated on reliability demonstration and on scaling-up technologies as much as possible in-house in order to produce enhanced MgB2 in relevant quantities (> 10 Kg/day) using cost-effective technologies