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Enhancement of J c and B irr on Binary and Alloyed in situ MgB 2 wires by PowerPoint PPT Presentation


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Enhancement of J c and B irr on Binary and Alloyed in situ MgB 2 wires by a new method: Cold High Pressure Densification. M.S.A. Hossain, C. Senatore, R. Flükiger DPMC & MANEP University of Geneva, 1211 Geneva, Switzerland. Outline Introduction

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Enhancement of J c and B irr on Binary and Alloyed in situ MgB 2 wires by

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Enhancement of Jc and Birr on

Binary and Alloyed in situ MgB2 wires by

a new method: Cold High Pressure Densification

M.S.A. Hossain, C. Senatore, R. Flükiger

DPMC & MANEP

University of Geneva,

1211 Geneva, Switzerland

.ExCo Meeting Tampere, 18.5.2009


Outline

Introduction

Cold High Pressure Densîfication on Binary MgB2 wires

Effects on microstructure and mass density

Effects on Jc and Birr

Model for explaining the pressure effects

Malic acid alloyed wires and tapes

Carbon alloyed wires and tapes

Conclusions

.ExCo Meeting Tampere, 18.5.2009


Definition: Field at which Jc = 1 x 104 A/cm2 : B(104)

Mass density in in situ wires:~ 50% of 2.67 g/cm3

High temperature – High pressure treatments

A Serquis et al., HIP on binary MgB2DB(104) = + 1T

Appl. Phys. Lett., 82(2003)2847

T Prikhna et al., 2kbar, on Ti alloyed MgB2DB(104) ~ + 1T

J. Physics: Conf. Series, 97(2008)012022

Conclusion:

Higher mass density leads to higher Jc and higher B(104) values

However, these methods are industrially not practicable

Need for new methods to enhance MgB2 mass densityin view of

industrial applications

.ExCo Meeting Tampere, 18.5.2009


How to enhance mass densities in MgB2?

* Infiltration method, initiated by Giunchi et al., 2005

Recently modified to wire application:

* K. Togano, J.M. Hur, A., Matsumoto, H. Kumakura, SuST 22(2008)

Highest Jc values so far in MgB2 wires: at 4.2 K, B(104) = 15 T

No mass density of the tubular filaments is given.

Probably very high mass density

* Cold high pressure Densification

* R. Flükiger, M.S.A. Hossain, C. Senatore, 2009

arxiv.org/ftp/arxiv/papers/0901/0901.4546, submitted to SuST

* M.S.A. Hossain, C. Senatore, R. Flükiger, M.A. Rindfleisch, M.J.

Tomsic, J.H. Kim, S.X. Dou, submitted to SuST.

.ExCo Meeting Tampere, 18.5.2009


Binary MgB2 wires

Fabrication of square wires, by applying pressure on 4 sides.

.ExCo Meeting Tampere, 18.5.2009


Binary Fe/MgB2 wire

1.0 mm 1.0 mm

Drawn to a square cross section After cold densification at 3 GPa

.ExCo Meeting Tampere, 18.5.2009


Fe/ MgB2 filament at the border of a region pressed at 1.9 GPa (polished sample)

.ExCo Meeting Tampere, 18.5.2009


Reduction of voids in a Fe/MgB2 wire reacted at 650°C for 1 hour

Without pressure Densified at 1.9 GPa.

.ExCo Meeting Tampere, 18.5.2009


Overall volume change in a Fe/MgB2 wire as a function of applied pressure

Initially square wires: higher volume reduction than round ones after densification

.ExCo Meeting Tampere, 18.5.2009


Mass densities of filaments in Fe/MgB2 wires.

Left scale: relative density dm of unreacted (Mg+B) mixture

Right scale: relative mass density df of reacted MgB2 filaments

.ExCo Meeting Tampere, 18.5.2009


Effect of pressure on Jc// at 4.2 K for a Fe/MgB2 wire

.ExCo Meeting Tampere, 18.5.2009


Correlation between Jc and MgB2 mass density df

df (%)

.ExCo Meeting Tampere, 18.5.2009


C4H6O5 Alloyed MgB2 tapes

C4H6O5 Alloyed MgB2 wires

.ExCo Meeting Tampere, 18.5.2009


Variation of Jc// with pressure

.ExCo Meeting Tampere, 18.5.2009


.ExCo Meeting Tampere, 18.5.2009


C4H6O5 Alloyed MgB2 wires

NbTi

Almost isotropic behavior, even at 4.2 K

.ExCo Meeting Tampere, 18.5.2009


C4H6O5 Alloyed MgB2 wires

Isotropic behavior at 4.2 and 20K

Highest Jc value reported so far for in situ wires

.ExCo Meeting Tampere, 18.5.2009


Pressure induces a densification and an increase of connectivity

However, this does not explain

* why the enhancement of Jc at 20K is so much higher

* Why Birr is enhanced

This effect can be understood by taking into account

the Tc distribution in the MgB2 filament

distribution model, based on specific heat measurements

.ExCo Meeting Tampere, 18.5.2009


.ExCo Meeting Tampere, 18.5.2009


Distribution model

Tc distribution in MgB2 bulk

Samples by calorimetry

Model: narrower distribution induced by high pressures

Senatore C, Lezza P, Lortz R, Shcherbakova O

Yeoh W K, Dou S X and Flükiger R

IEEE Trans. Appl. Supercond. 17(2007)2941

.ExCo Meeting Tampere, 18.5.2009


Distribution model

Tc onset is the same, but low Tctailisshifted to higher values

the superconducting surface increases

The existence of a Tc distribution meansthatthereisalso a distribution of Birr and Bc2. Increase of Birr

.ExCo Meeting Tampere, 18.5.2009


Conclusions:

Higher MgB2 mass density has been obtained by

Cold High Pressure Densification (CHPD)

Strong enhancement of Jc and Birr has been observed in binary MgB2 wires4.2K/10T: DTc = 53%, 20K/5T: DTc = 300%

C4H6O5 alloyed MgB2 wires:

4.2K/10T: DTc = 100%, 20K/5T: DTc = 400%

Square MgB2 wires with practically isotropic properties exhibited the highest value of Jc reported so far: B(104) = 12.7 T at 4.2K.

B(104) = 6.0 T at 20K

Further improvements are expected after optimizing the densification process, shifting the crack-free limit to higher pressures

CHPD has the potential for industrial production of long MgB2 wires

.ExCo Meeting Tampere, 18.5.2009


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