Critical current density and strain effects of Fe/MgB 2 tapes with different particle sizes...

Critical current density and strain effects of Fe/MgB2 tapes with different particle sizes

Université de Genève

Paola Lezza

Co-workers: H. L. SuoV. AbächerliD. UgliettiN. ClaytonC. SenatoreN. MusolinoR. Flükiger

Département de Physique de la Matière Condensée, Université de Genève, 24, quai Ernst Ansermet, 1211 Genève, Switzerland


Present state of critical current density in MgB2

Tapes preparation

Critical current density Jc for 3 h and 100 h ball milled tapes

n-values

Inductive and transport measurements on 100 h ball milled tape

Irreversibility fields Birr

Strain Effect on 100 h ball milled tape

Conclusion

Outline


Present state, wires and tapes

Wang

Giunchi

Gümbel

Unige

Dhallé

Goldacker

Wire

Wire

Tape

Bulk

Tape

Bulk

Fe

Fe

Soft S.

Fe

R. Flukiger et al., « Superconducting properties of MgB2 tapes and wires », Physica C 385 (2003) 286-305


Present state, films

Bu

Kang

Komori

Unige

Film

YSZ

Tape

Film

Film

Al2O3

None

Al2O3


0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15101

102

103

104

105

106

107

108

Bu Geneva

(tape)//

MgB2

//

20 K4.2 K

Films

0H (T)

J c (A

/cm

2 )

Bu Kang Komori Geneva

(tape)


Present state, effect of additives

Dou

Zhao

Wang

Unige

Wire

Ti

Y2O3

Tape

Bulk

Bulk

SiC

None


0 1 2 3 4 5 6 7 8 9 101112131415100

101

102

103

104

105

106

107

Geneva, without additions

Dou Zhao Wang

Effect of Additives

20 K

4.2 K

MgB2

Dou Zhao Wang

0H (T)J c(

A/c

m2 )


Preparation

Ball milling under Ar

P. I. T.

Swege

Draw

Flat rolling

in= 5 mm

out= 8 mm

= 3.85 mm

= 2 mm

Tape 4 x 0.38 mm2

P.I.T.

Flat rolling

Final Tape

MgB2

0 1 2 3 4 5 6 7 8 9 101112131415

101

102

103

104

105

100 h ball milling in Ar B tape surface

100 h ball milling in Ar B tape surface

B(T)

J c(A

/cm

2 )

Jc at 4.2 K for different powder grain sizes


0.1 1 10 60

3 h ball milled

100 h ball milled

100

90

80

70

60

50

40

30

20

10

00 1 2 3 4 5 6 7 8 9 101112131415

101

102

103

104

105

100 h ball milling in Ar


B(T)

J c(A

/cm

2 )

100

90

80

70

60

50

40

30

20

10

0 0.1 1 10 60

4 5 6 7 8 9 10 11 12 13

10

100



B(T)

n-va

lue

n values for Fe/MgB2 tape


0.1 V/cm

1 V/cm

I

n=148, 4.5 T

n>30, 9.5 T

0.1 V/cm

1 V/cm

I

log-log

Transport measurements on annealed Fe/MgB2 tape 100 h ball milled


1 2 3 4 5 6 7 8 9 10 11 12 13 14 1510

1

102

103

104

105

30 K20 K 4.2 K

10 K

B(T)

J c(A

/cm

2 )

Irreversibility field as a function of grain size


Definitions:


1) A frequently used definition is based on the resistively measured superconducting transition, the criterion being the 10% of RN or the intersection of the extrapolated linear part of R(T) with R=0

2) The field at which the the inductively measured critical current vanishes

10% RN

R(T)

T

R(T)

T

Jc

B

M

H

Irreversibility field as a function of grain size


Third Definition:3) The onset of the third harmonic susceptibility, in presence of a magnetic field Hdc>> Hac results from a crossover between a regime in which the system response is flux low dominated (no harmonic signal) and one which is pinnig dominated. The onset of the third harmonic thus corresponds to a non-zero critical current density J c

5 10 15 20 25 30 35 400

2

4

6

8

10

12

14

100 h ball milling

Birr (

T)

T(K)

3 h ball milling

0 2 4 6 8

-0.02

0.00

0.02

0.04

0.06

0.08

3 (S

I u

nits

)

T = 20 KHAC = 8 Oef = 1607 Hz

0H

DC (Tesla)

'3

"3

|3|

0.00 0.05 0.10 0.15 0.20 0.25 0.30 0.35 0.4005

10152025303540455055606570

9 T

7 T

strain (%)I c

(A)

Strain Effect on MgB2 long tape 100 h ball milled


Strain gauges

Modified Walters Spiral (WASP)

MgB2 Tape

d=26 cm

0.00 0.05 0.10 0.15 0.20 0.25 0.30 0.35 0.4005

1015202530354045505560

9 T

7 T

strain (%)

n-va

lue


Conclusion

The actual state of the critical current densities has been presented, and compared with our latest data.

The critical current densities Jc and the n-values of the Fe/MgB2 tapes, 3 h and 100 h ball milled have been compared. An enhancement is obtained for the smaller particle size.

The critical current densities Jc in the two configurations with the tape surface parallel and perpendicular to the magnetic field direction have been measured. A strong difference has been obtained, reflecting a partial texture of the grains.

The various criteria of the irreversibility field Birr have been discussed.

Strain effects on 100 h ball milled tape have been measured on 80 cm length with a modified Walters Spiral. The degradation of the critical current and the n-values confirming the pre-stress model.

3 4 5 6 7 8 9 10 11 12 13 14 15

10

100

100 h ball milling in ArB tape surface

100 h ball milling in ArB tape surface

B(T)

n-va

lue

n values for Fe/MgB2 tape


Critical current density and strain effects of Fe/MgB 2 tapes with different particle sizes...

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