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Superconducting properties of V2(Hf, Zr) laves phase multifilamentary wires
Journal
of Nuclear
Materials
SUPERCONDUCTING WIRES K. INOUE, National
T. KURODA
Research
815
133&134 (1985) 815-818
PROPERTIES
OF V,(Hf, Zr) LAVES PHASE MULTIFILAMENTARY
and K. TACHIKAWA
Instrtute for Metals, Sengen,
Sakura.
Ntthartgun,
Iharaki
30.5, Jupan
Superconducting properties have been studied for newly developed V,(Hf. Zr) muittfilamentary wires. At 4.2 K. a poHcl of 22 T and an overall J, of 1 x lo4 A/cm* at 17 T are obtained for these wires. At 1.8 K in a field of 15 T. the overall J, of these wires are twice as large as that of the bronze processed Nb,Sn multifilamentary wire. The enhanced J, at reduced temperature scaling law of the pinning force density. p,,Hc2 may be attributed to the rapid increase in pLoHc, by using the temperature measured in pulsed fields is about 28 T at 2.0 K. According to the temperature is estimated to be 2 x lo4 A/cm*. Thus, the present V?(Hf. Zr) multifilamentary high magnetic fields in superfluid liquid helium.
1. Introduction Large current carrying capacities in high magnetic fields, low AC losses, and high stability with respect to mechanical stress and neutron irradiation are required in the practical application of superconductors to large scale magnet systems such as magnetic fusion reactor. On the other hand, V,Hf-based superconductors are very attractive for fusion reactor magnets use due to their promising combination of high upper critical fields, poHc, exceeding 20 T at 4.2 K [l] and insensitivity of superconducting properties to both neutron irradiation [2] and mechanical strain [3]. Pseudobinary laves phase compounds, V,(Hf, Zr), exhibit higher poHc, and superconducting transition temperature, c. than those of binary V,Hf and V,Zr [4]. Recently these materials have been successfully fabricated into multifilamentary wires by the composite diffusion process, where a composite of a V-l at.% Hf alloy matrix with Zr-Hf alloy cores is cold-drawn to a wire and then reacted to form Laves phase compound layers by a diffusion reaction between the matrix and the cores. In the present study the superconducting properties of V,(Hf,Zr) multifilamentary wires with various hafnium contents in the Zr-Hf alloy cores have been examined.
2. Experimental procedure The fabrication process for V,(Hf, Zr) multifilamentary wires was as follows. Arc-melted V-l at.% Hf and Zr-(25, 35, 40, 45, 50) at.% Hf alloy ingots were coldworked into rods and used as the matrix and the core, respectively. The nineteen Zr-Hf alloy rods were inserted into drilled holes in a V-l at.% Hf alloy matrix. The composite was cold-drawn to a wire with intermediate anneals at about 800°C. cut into short pieces and packed into a V-l at.% Hf alloy tube. This composite was again cold-drawn to final diameter and then heat treated at 850-1050°C to form V,(Hf, Zr) layers 0022-3115/85/$03.30 0 Elsevier Science Publishers (North-Holland Physics Publishing Division)
B.V.
scaling law. the overall JL for 1.X K and at 20 T wires are very promising for use in generattng
via diffusion reaction between the V-Hf and the ZrrHf alloys. The values of T, and poHc, were measured by the standard resistive method and defined as the midpoints of the resistive transition curves. pLoHc, measurements at 2.0 to 4.2 K were carried out using a pulsed magnet with a rise time of 10 ms in a controlled pressure liquid helium environment. where temperatures were controlled by changing the helium vapour pressures. The poH,., above 4.2 K was measured in a steady magnetic field with temperatures monitored using a temperature sensitive SrTiO, capacitor. Critical current. I,. measurements at 4.2 K were performed in steady magnetic inductions up to 20 T. The I, was defined as a current where a voltage of 1 PV appeared across the potential leads separated by 10 mm. The I, below 4.2 K was measured in a pressure-controlled liquid helium bath.
3. Results and discussions 19, 133, 361 and 1425-core V,(Hf, Zr) multifilamentary wires were prepared. Volume ratios of the V-l at.% Hf matrix to the Zr-Hf cores are about 4.3 for all the samples. Fig. 1 shows a typical cross-section of 1425~core V,(Hf. Zr) multifilamentary wire consisting of Zr-45 at.% Hf cores and V-l at.% Hf matrix. Fig. 2 shows overall .I, versus magnetic induction curves of 1425-core V,(Hf, Zr) multifilamentary wires with various Zr-Hf alloy compositions. The largest J, values in magnetic inductions below 10 T are obtained for Zr-(40-50) at.% Hf core wires. On the other hand, Zrr50 at.% Hf core wires show the largest J, values in magnetic inductions higher than 13 T due to their high poHc,. Overall J, values of about 1 X lo4 A/cm2 are obtained at 4.2 K and 17 T for Zr-(45-50) at.% Hf core wires. These overall J, values are as high as those of the commercial Nb,Sn multifilamentary wires. Fig 3 shows <, p0HCz(4.2 K) and overall J, (4.2 K, 10 T) of 133-core V,(Hf, Zr) multifilamentary wires
816
K. Inoue et 01. / Superconductwrty
Fig. 1. Cross-section
of 1425core
V,(Hf,
Zr) multifilamentary at.‘% Hf matrix and
wire, 1 mm in diameter, consisting of V-l Zr-45
properties of V,(Hl; Zr) Latw phux
at.% Hf cores.
t
“25
30
0 as a function
of hafnium content in the ZrrHf alloy core. These critical parameters improve with increasing hafnium content. T, and overall J,(4.2 K, 10 T) show the maximum values of 9.9 K and 3.5 x lo4 A/cm*, respectively, when the hafnium content in the core is 45 at.%. The highest pLoH,,(4.2 K) of 22.1 T is obtained for the Zr-50 at.% Hf core wire. A heat treatment temperature of 950-1025°C is the most favorable for obtaining
Hf
,,
105 :
1025’C Y 20 hr -
I
I
I Zr-50ot%Hf
‘\
Core
1
Zr-SOat%Hf Core (d-2.6 .Xso=9)
25
Zr-45ut%Hf
I-
2m
; I
0 L
I
Core
30
’A loGIZr-35at%Hf n ee,
50
highest values of Tc, p,,l-I,, and overall -I, in the V,(Hf, Zr) wire. Curves of pLoHc, versus temperature for 133-core
4 “E
LS (at%)
the
Core
rJ+Oat%Hf
60
Fig. 3. c, p,,H,,(4.2 K) and overall J,(4.2 K, 10 T) of 133 -core multifilamentary wires heat treated at quoted conditions as a function of hafnium content in the Zr-Hf alloy core.
35
Zr-&at%Hf
35 Content
950*CXJOhr
Core
20 0 =
15
10
V2(Hf.Zr)
MF
5
Wire
0 0
2
4
6 T
I
IO'1
0
4
I 12
6
B
16
20
(T)
Fig. 2. Overall J, at 4.2 K versus magnetic induction curves for V,(Hf, Zr) multifilamentary wires with Zr-(25, 35.40, 45, 50) at.% Hf aloy cores heat treated at quoted conditions.
0
10
(K)
Fig. 4. poH,, versus temperature curves for V,(Hf, Zr) multifilamentary wires. The dotted line shows the calculated p0 H,, assuming A,, = cc and OL= 2.6 for the Zr-50 at.% Hf core wire. The solid lines show those assuming (A,, = 9, a = 2.6). (A,,, = 6. u = 2.5) and (A,,, = 5, 01= 2.5) for the Zr-50 at.% Hf. Zr-45 at.% Hf and Zr-35 at.% Hf core wires. respectively.
K. Inoue et al. / Superconductivity
\I,(Hf, Zr) multifilamentary wires are shown in fig. 4. The pLoIi,, of V*(Hf, Zr) wires increase much more rapidly with decreasing temperature than those of Al5 type compounds. This rapid increase in p,,H,, leads to a rapid increase in -I, at reduced temperatures as expected from the temperature scaling law of the flux pinning force described later. Values of the paramagnetic limitation parameter, a, calculated using a = -0.533 x (dp,HJdT),_TL [5], are 2.4 to 2.8, scarcely dependent on the hafnium content and the heat treatment temperature. These (Y values for V2(Hf, Zr) wires are much higher than those for other high-field superconductors; (Y of Nb,Sn is 1.1. VI(Hf, Zr) is known to have a large electronic specific-heat coefficient, y, leading to large (Y [4]. Werthamer et al. [6] have calculated the temperature dependence of p,,H,, taking into account both the paramagnetic effect and the spin-orbit scattering effect. The measured temperature dependence of p,,HC2 values in the present study agrees well with that calculated by assuming the values of the spin-orbit scattering parameter, X,,, are 5, 6, and 9 for the Zr-35 at.% Hf, Zr-45 at.% Hf and Zr-50 at.% Hf core wires, respectively. The spin-orbit scattering effect increases p,,H,, at low temperatures by compensating for the paramagnetic effect which reduces pLot-I,,. According to Neuringer et al. [7], X,, is increased by the addition of heavy elements such as hafnium. The increase of hafnium content in the V,(Hf, Zr) layer should increase p0 I-I,, at low temperature through the increase of the spin-orbit scattering effect, as indicated in fig. 4. For Zr-50 at.% Hf core wires the measured pOHCl,, in pulsed fields is
817
properties of r/,(Hj Zr) Laves phase
about 28 T at 2.0 K, higher than that of the commercial Nb,Sn multifilamentary wire. The overall J, of V,(Hf, Zr) multifilamentary wire is rapidly increased with decreasing temperature. The Jc(1.8 K)/J,(4.2 K) ratio at 12.5 T versus heat treatment temperature curves for \I,(Hf, Zr) multifilamentary wires with different core compositions are shown in fig. 5. Ratios of Jc(1.8 K)/J,(4.2 K) for V;(Hf, Zr) wires are 2.2 to 3.2 at 12.5 T, while that for the Nb,Sn wire is only about 1.4. This difference in J, gain by reducing the temperature for both materials is expected to become even larger in magnetic inductions higher than 12.5 T. With increasing hafnium content and heat treatment temperature, 5,(1.8 K)/J,(4.2 K) ratios at 12.5 T tend to be decreased. Generally, the pinning force density, P = J, X B, obeys the temperature scaling law [8], P = (p. t-l,.)“f( b), where f(b) is only a function of reduced magnetic induction, b = B/pOHC2. Fig 6 shows overall .I, versus magnetic induction curves for \I,(Hf, Zr) multifilamentary wires with 133 Zr-45 at.% Hf cores, and compares these with Nb,Sn multifilamentary wire which is a composite of 180-core Nb/Cu-7.4 at.% Sn with a bronze ratio of 2.7. For V,(Hf, Zr) multifilamentary wires, the increase in overall J, at reduced temperatures is especially remarkable in higher magnetic inductions. Therefore, V2(Hf, Zr) multifilamentary wires show larger overall -I, at 1.8 K than those of Nb,Sn multifilamentary wire in magnetic inductions higher than 9 T. Overall -I, values calculated by using the temperature scaling
,7
I
I Zr-35pt%Hf
Core
3.1 K
3
z
-I
i V,(Hf,Zr)
Nb,Sn 4 MF Wire
1
Zr-50at%Hf
hU
I
at
I Core
I MF Wir,e
12.5 T IO00
Heat
Treatment Temperature (“C ) K)/J,(4.2 K) ratio at 12.5 T for V,(Hf,Zr)
Fig. 5. J,(1.8 multifilamentary wires with Zr-(35,40,45,50) at.% Hf cores as a function of heat treatment temperature. The ratio of Nb,Sn multifilamentary wire is denoted by an arrow.
B
(T)
Fig. 6. Overall JC versus magnetic induction curves for V,(Hf, Zr) multifilamentary wire with Zr-45 at.% Hf core at 1.8-4.2 K. Those of Nb,Sn multifilamentary wire are also exhibited. Dotted lines indicate calculated values found by using the temperature scaling law.
law are also shown in fig. 6 by dotted lines, for magnetic inductions above 12.5 T. The overall .I, extrapolated to 20 T is about 2 X lo4 A/cm2 at 1.8 K, much higher than that of the commercial multifilamentary wires developed so far.
Acknowledgement
The authors would like to express thetr sincere thanks Professor H. Noto and Dr K. Watanabe of the Research Institute for Iron, Steel. and Other Metals ol Tohoku University for measuring the critical currents by their 20 T hybrid magnet. to
4. Conclusions Multifilamentary wires of V,(Hf, Zr) with Zr-(40-50) at.% Hf cores shows overall J, and poH,, as high as those of the commercial Nb,Sn multifilamentary wire at 4.2 K. Furthermore, the overall .I, of V,(Hf, Zr) multifilamentary wires is increased rapidly with reducing temperature and becomes twice as large as that of the commercial Nb,Sn mult~filamentary wire at 1.8 K and 15 T. The enhanced f, at reduced temperatures may be caused by the rapid increase in p,,H,... The pLoHC, value of the Zr-50 at.% Hf core wire is about 28 T at 2.0 K. The estimated value of overall 1, at 1.8 K is 2 X lo4 A/cm2 at 20 T. The V?(Hf. Zr) nlult~filamentary wire is very promising for use in magnets generating high magnetic fields above 18 T in pressurized liquid He II. They may find application in high-field magnets for fusion reactors.
References
PI K. Inoue and K. Tachikawja, Proc. Applied Superconductivity Conf., IEEE Cat. No. 72 CHO 682 TABSC (1972) 415. PI B.S. Brown. J.W. Hafstron and T.E. Klippert. J. Appi. Phys. 48 (1977) 1759. and J.W. Ekin, Appl. [31 W. Wada. K. lnoue, K. Tachikawa Phys. Lett. 40 (1982) X44. 141 K. lnoue and K. Tachikawa. J. Japan Inst. Metals 39 (1975) 1265. ibid.. 1274. I51 K. Maki, Phys. Rev. 14X (1966) 362. E. Helfand and P.C. Hohenberge. Phys. @I N.R. Werthamer, Rev. 147 (1966) 295. 171 L.J. Neurmger and Y. Shapira, Phys. Rev. Lctt. 17 (1966) 81. PI E.J. Kramer, J. Appl. Phys. 44 (1973) 1360.
of Nuclear
Materials
SUPERCONDUCTING WIRES K. INOUE, National
T. KURODA
Research
815
133&134 (1985) 815-818
PROPERTIES
OF V,(Hf, Zr) LAVES PHASE MULTIFILAMENTARY
and K. TACHIKAWA
Instrtute for Metals, Sengen,
Sakura.
Ntthartgun,
Iharaki
30.5, Jupan
Superconducting properties have been studied for newly developed V,(Hf. Zr) muittfilamentary wires. At 4.2 K. a poHcl of 22 T and an overall J, of 1 x lo4 A/cm* at 17 T are obtained for these wires. At 1.8 K in a field of 15 T. the overall J, of these wires are twice as large as that of the bronze processed Nb,Sn multifilamentary wire. The enhanced J, at reduced temperature scaling law of the pinning force density. p,,Hc2 may be attributed to the rapid increase in pLoHc, by using the temperature measured in pulsed fields is about 28 T at 2.0 K. According to the temperature is estimated to be 2 x lo4 A/cm*. Thus, the present V?(Hf. Zr) multifilamentary high magnetic fields in superfluid liquid helium.
1. Introduction Large current carrying capacities in high magnetic fields, low AC losses, and high stability with respect to mechanical stress and neutron irradiation are required in the practical application of superconductors to large scale magnet systems such as magnetic fusion reactor. On the other hand, V,Hf-based superconductors are very attractive for fusion reactor magnets use due to their promising combination of high upper critical fields, poHc, exceeding 20 T at 4.2 K [l] and insensitivity of superconducting properties to both neutron irradiation [2] and mechanical strain [3]. Pseudobinary laves phase compounds, V,(Hf, Zr), exhibit higher poHc, and superconducting transition temperature, c. than those of binary V,Hf and V,Zr [4]. Recently these materials have been successfully fabricated into multifilamentary wires by the composite diffusion process, where a composite of a V-l at.% Hf alloy matrix with Zr-Hf alloy cores is cold-drawn to a wire and then reacted to form Laves phase compound layers by a diffusion reaction between the matrix and the cores. In the present study the superconducting properties of V,(Hf,Zr) multifilamentary wires with various hafnium contents in the Zr-Hf alloy cores have been examined.
2. Experimental procedure The fabrication process for V,(Hf, Zr) multifilamentary wires was as follows. Arc-melted V-l at.% Hf and Zr-(25, 35, 40, 45, 50) at.% Hf alloy ingots were coldworked into rods and used as the matrix and the core, respectively. The nineteen Zr-Hf alloy rods were inserted into drilled holes in a V-l at.% Hf alloy matrix. The composite was cold-drawn to a wire with intermediate anneals at about 800°C. cut into short pieces and packed into a V-l at.% Hf alloy tube. This composite was again cold-drawn to final diameter and then heat treated at 850-1050°C to form V,(Hf, Zr) layers 0022-3115/85/$03.30 0 Elsevier Science Publishers (North-Holland Physics Publishing Division)
B.V.
scaling law. the overall JL for 1.X K and at 20 T wires are very promising for use in generattng
via diffusion reaction between the V-Hf and the ZrrHf alloys. The values of T, and poHc, were measured by the standard resistive method and defined as the midpoints of the resistive transition curves. pLoHc, measurements at 2.0 to 4.2 K were carried out using a pulsed magnet with a rise time of 10 ms in a controlled pressure liquid helium environment. where temperatures were controlled by changing the helium vapour pressures. The poH,., above 4.2 K was measured in a steady magnetic field with temperatures monitored using a temperature sensitive SrTiO, capacitor. Critical current. I,. measurements at 4.2 K were performed in steady magnetic inductions up to 20 T. The I, was defined as a current where a voltage of 1 PV appeared across the potential leads separated by 10 mm. The I, below 4.2 K was measured in a pressure-controlled liquid helium bath.
3. Results and discussions 19, 133, 361 and 1425-core V,(Hf, Zr) multifilamentary wires were prepared. Volume ratios of the V-l at.% Hf matrix to the Zr-Hf cores are about 4.3 for all the samples. Fig. 1 shows a typical cross-section of 1425~core V,(Hf. Zr) multifilamentary wire consisting of Zr-45 at.% Hf cores and V-l at.% Hf matrix. Fig. 2 shows overall .I, versus magnetic induction curves of 1425-core V,(Hf, Zr) multifilamentary wires with various Zr-Hf alloy compositions. The largest J, values in magnetic inductions below 10 T are obtained for Zr-(40-50) at.% Hf core wires. On the other hand, Zrr50 at.% Hf core wires show the largest J, values in magnetic inductions higher than 13 T due to their high poHc,. Overall J, values of about 1 X lo4 A/cm2 are obtained at 4.2 K and 17 T for Zr-(45-50) at.% Hf core wires. These overall J, values are as high as those of the commercial Nb,Sn multifilamentary wires. Fig 3 shows <, p0HCz(4.2 K) and overall J, (4.2 K, 10 T) of 133-core V,(Hf, Zr) multifilamentary wires
816
K. Inoue et 01. / Superconductwrty
Fig. 1. Cross-section
of 1425core
V,(Hf,
Zr) multifilamentary at.‘% Hf matrix and
wire, 1 mm in diameter, consisting of V-l Zr-45
properties of V,(Hl; Zr) Latw phux
at.% Hf cores.
t
“25
30
0 as a function
of hafnium content in the ZrrHf alloy core. These critical parameters improve with increasing hafnium content. T, and overall J,(4.2 K, 10 T) show the maximum values of 9.9 K and 3.5 x lo4 A/cm*, respectively, when the hafnium content in the core is 45 at.%. The highest pLoH,,(4.2 K) of 22.1 T is obtained for the Zr-50 at.% Hf core wire. A heat treatment temperature of 950-1025°C is the most favorable for obtaining
Hf
,,
105 :
1025’C Y 20 hr -
I
I
I Zr-50ot%Hf
‘\
Core
1
Zr-SOat%Hf Core (d-2.6 .Xso=9)
25
Zr-45ut%Hf
I-
2m
; I
0 L
I
Core
30
’A loGIZr-35at%Hf n ee,
50
highest values of Tc, p,,l-I,, and overall -I, in the V,(Hf, Zr) wire. Curves of pLoHc, versus temperature for 133-core
4 “E
LS (at%)
the
Core
rJ+Oat%Hf
60
Fig. 3. c, p,,H,,(4.2 K) and overall J,(4.2 K, 10 T) of 133 -core multifilamentary wires heat treated at quoted conditions as a function of hafnium content in the Zr-Hf alloy core.
35
Zr-&at%Hf
35 Content
950*CXJOhr
Core
20 0 =
15
10
V2(Hf.Zr)
MF
5
Wire
0 0
2
4
6 T
I
IO'1
0
4
I 12
6
B
16
20
(T)
Fig. 2. Overall J, at 4.2 K versus magnetic induction curves for V,(Hf, Zr) multifilamentary wires with Zr-(25, 35.40, 45, 50) at.% Hf aloy cores heat treated at quoted conditions.
0
10
(K)
Fig. 4. poH,, versus temperature curves for V,(Hf, Zr) multifilamentary wires. The dotted line shows the calculated p0 H,, assuming A,, = cc and OL= 2.6 for the Zr-50 at.% Hf core wire. The solid lines show those assuming (A,, = 9, a = 2.6). (A,,, = 6. u = 2.5) and (A,,, = 5, 01= 2.5) for the Zr-50 at.% Hf. Zr-45 at.% Hf and Zr-35 at.% Hf core wires. respectively.
K. Inoue et al. / Superconductivity
\I,(Hf, Zr) multifilamentary wires are shown in fig. 4. The pLoIi,, of V*(Hf, Zr) wires increase much more rapidly with decreasing temperature than those of Al5 type compounds. This rapid increase in p,,H,, leads to a rapid increase in -I, at reduced temperatures as expected from the temperature scaling law of the flux pinning force described later. Values of the paramagnetic limitation parameter, a, calculated using a = -0.533 x (dp,HJdT),_TL [5], are 2.4 to 2.8, scarcely dependent on the hafnium content and the heat treatment temperature. These (Y values for V2(Hf, Zr) wires are much higher than those for other high-field superconductors; (Y of Nb,Sn is 1.1. VI(Hf, Zr) is known to have a large electronic specific-heat coefficient, y, leading to large (Y [4]. Werthamer et al. [6] have calculated the temperature dependence of p,,H,, taking into account both the paramagnetic effect and the spin-orbit scattering effect. The measured temperature dependence of p,,HC2 values in the present study agrees well with that calculated by assuming the values of the spin-orbit scattering parameter, X,,, are 5, 6, and 9 for the Zr-35 at.% Hf, Zr-45 at.% Hf and Zr-50 at.% Hf core wires, respectively. The spin-orbit scattering effect increases p,,H,, at low temperatures by compensating for the paramagnetic effect which reduces pLot-I,,. According to Neuringer et al. [7], X,, is increased by the addition of heavy elements such as hafnium. The increase of hafnium content in the V,(Hf, Zr) layer should increase p0 I-I,, at low temperature through the increase of the spin-orbit scattering effect, as indicated in fig. 4. For Zr-50 at.% Hf core wires the measured pOHCl,, in pulsed fields is
817
properties of r/,(Hj Zr) Laves phase
about 28 T at 2.0 K, higher than that of the commercial Nb,Sn multifilamentary wire. The overall J, of V,(Hf, Zr) multifilamentary wire is rapidly increased with decreasing temperature. The Jc(1.8 K)/J,(4.2 K) ratio at 12.5 T versus heat treatment temperature curves for \I,(Hf, Zr) multifilamentary wires with different core compositions are shown in fig. 5. Ratios of Jc(1.8 K)/J,(4.2 K) for V;(Hf, Zr) wires are 2.2 to 3.2 at 12.5 T, while that for the Nb,Sn wire is only about 1.4. This difference in J, gain by reducing the temperature for both materials is expected to become even larger in magnetic inductions higher than 12.5 T. With increasing hafnium content and heat treatment temperature, 5,(1.8 K)/J,(4.2 K) ratios at 12.5 T tend to be decreased. Generally, the pinning force density, P = J, X B, obeys the temperature scaling law [8], P = (p. t-l,.)“f( b), where f(b) is only a function of reduced magnetic induction, b = B/pOHC2. Fig 6 shows overall .I, versus magnetic induction curves for \I,(Hf, Zr) multifilamentary wires with 133 Zr-45 at.% Hf cores, and compares these with Nb,Sn multifilamentary wire which is a composite of 180-core Nb/Cu-7.4 at.% Sn with a bronze ratio of 2.7. For V,(Hf, Zr) multifilamentary wires, the increase in overall J, at reduced temperatures is especially remarkable in higher magnetic inductions. Therefore, V2(Hf, Zr) multifilamentary wires show larger overall -I, at 1.8 K than those of Nb,Sn multifilamentary wire in magnetic inductions higher than 9 T. Overall -I, values calculated by using the temperature scaling
,7
I
I Zr-35pt%Hf
Core
3.1 K
3
z
-I
i V,(Hf,Zr)
Nb,Sn 4 MF Wire
1
Zr-50at%Hf
hU
I
at
I Core
I MF Wir,e
12.5 T IO00
Heat
Treatment Temperature (“C ) K)/J,(4.2 K) ratio at 12.5 T for V,(Hf,Zr)
Fig. 5. J,(1.8 multifilamentary wires with Zr-(35,40,45,50) at.% Hf cores as a function of heat treatment temperature. The ratio of Nb,Sn multifilamentary wire is denoted by an arrow.
B
(T)
Fig. 6. Overall JC versus magnetic induction curves for V,(Hf, Zr) multifilamentary wire with Zr-45 at.% Hf core at 1.8-4.2 K. Those of Nb,Sn multifilamentary wire are also exhibited. Dotted lines indicate calculated values found by using the temperature scaling law.
law are also shown in fig. 6 by dotted lines, for magnetic inductions above 12.5 T. The overall .I, extrapolated to 20 T is about 2 X lo4 A/cm2 at 1.8 K, much higher than that of the commercial multifilamentary wires developed so far.
Acknowledgement
The authors would like to express thetr sincere thanks Professor H. Noto and Dr K. Watanabe of the Research Institute for Iron, Steel. and Other Metals ol Tohoku University for measuring the critical currents by their 20 T hybrid magnet. to
4. Conclusions Multifilamentary wires of V,(Hf, Zr) with Zr-(40-50) at.% Hf cores shows overall J, and poH,, as high as those of the commercial Nb,Sn multifilamentary wire at 4.2 K. Furthermore, the overall .I, of V,(Hf, Zr) multifilamentary wires is increased rapidly with reducing temperature and becomes twice as large as that of the commercial Nb,Sn mult~filamentary wire at 1.8 K and 15 T. The enhanced f, at reduced temperatures may be caused by the rapid increase in p,,H,... The pLoHC, value of the Zr-50 at.% Hf core wire is about 28 T at 2.0 K. The estimated value of overall 1, at 1.8 K is 2 X lo4 A/cm2 at 20 T. The V?(Hf. Zr) nlult~filamentary wire is very promising for use in magnets generating high magnetic fields above 18 T in pressurized liquid He II. They may find application in high-field magnets for fusion reactors.
References
PI K. Inoue and K. Tachikawja, Proc. Applied Superconductivity Conf., IEEE Cat. No. 72 CHO 682 TABSC (1972) 415. PI B.S. Brown. J.W. Hafstron and T.E. Klippert. J. Appi. Phys. 48 (1977) 1759. and J.W. Ekin, Appl. [31 W. Wada. K. lnoue, K. Tachikawa Phys. Lett. 40 (1982) X44. 141 K. lnoue and K. Tachikawa. J. Japan Inst. Metals 39 (1975) 1265. ibid.. 1274. I51 K. Maki, Phys. Rev. 14X (1966) 362. E. Helfand and P.C. Hohenberge. Phys. @I N.R. Werthamer, Rev. 147 (1966) 295. 171 L.J. Neurmger and Y. Shapira, Phys. Rev. Lctt. 17 (1966) 81. PI E.J. Kramer, J. Appl. Phys. 44 (1973) 1360.