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First experiments with a high-Tc superconducting magnet
Physica C 153-155 (1988) 1417-1418 North-Holland, Amsterdam
FIRST
EXPERIMENTS
WITH
A HIGH-T
C
SUPERCONDUCTING
MAGNET
I. KIRSCHNER, M. LAMM x, T. PORJESZ, J. M~TRAI x, GY. KOV~CS, T. TRAGER x, T. K~RM~N, J. GYORGY x and G.
ZSOLT
D e p a r t m e n t for Low T e m p e r a t u r e Physics, EStvSs University, Budapest, Hungary, XCentral Research and Design Institute for Silicate Industry, Budapest, H u n g a r y
A high-T c ceramic rings,
made
superconducting
magnet
of an Y I B a 2 C u 3 0 7 _ x compound.
of c y l i n d r i c a l The magnet
shape
consisting
was
consctructed
of
of 20 i n d i v i d u a l
rings can produce a magnetic field of 0.02 T (exactly 207 0e) at a s u p e r c o n d u c t i n g current of 65 A. To avoid the problems of the J o u l e - h e a t i n g on the r e s i s t i v i t y of ohmic contacts, the magnet was supplied m a g n e t i c a l l y by a contactless, i n d u c t i v e method. In this way, the magnetic field is limited only by the s u p e r c o n d u c t i n g p a r a m e t e r s of the material.
I. I N T R O D U C T I O N The high field magnets, the high power electric energy transport and the rotating electrical machines of d i f f e r e n t kinds are very prospective areas of the a p p l i c a t i o n for the h i g h - T superconducting ceramics. Initiated o~ this basis we began planning and d e v e l o p i n g high-T suc p e r c o n d u c t i n g magnets. These i n v e s t i g a tions are based on our e x p e r i e n c e s in a n a l i t i c a l and computer aided design, b u i l d i n g and operating (1,2,3,4) of conventional s u p e r c o n d u c t i n g magnets and in basic research (5,6,7) on high-T c superconductors. In this paper we present the c o n s t r u c tion and the most important p a r a m e t e r s of a magnet, shown in Fig.l, made of 20 pieces of high-T s u p e r c o n d u c t i n g ceramic rlngs. Thls magnet was e n e r g i z e d by a contactless magnetic i n d u c t i o n method. •
.
ments. S u p p o s i n g an e x c i t a t i o n current having a nominal value of 100 A and a contact r e s i s t i v i t y of about 0.1-0.01 ohms, the d i s s i p a t e d energy is 100 W to 1 kW, being too much to be cooled.
C
2. C O N S T R U C T I O N OF THE MAGNET For planning and building of a magnet made of a rigid and brittle h i g h - T superc o n d u c t i n g ceramics we had two cholces: 1. making a c o n v e n t i o n a l solenoid and s u p p l y i n g it by the aid of a d.c. current source, 2. r e a l i z i n g a magnet d i f f e r e n t l y from the accustomed, c o n s i s t i n g of individual rings, supplying with energy by induction. The first v a r i a t i o n is backed up by usual mode of action and the easily available r e g u l a t e d current sources. The constr u c t i o n of this type of ceramic magnets seemed to be very difficult because of the contact resistances arising from the current lead to s u p e r c o n d u c t o r junctions and from the coupling of structural ele-
0921-4534/88/$03.50 © Elsevier Science Publishers B.V. (North-Holland Physics Publishing Division)
Fig.1.
Picture
of the magnet
C o n s i d e r i n g the above m e n t i o n e d cir3umstances we chose the version of the magnet of second kind, built up of individual rings and m a g n e t i c a l l y energized. In this case, using s u f f i c i e n t l y thin and stabilized rings, the upper limit of the magnetic field which can be produced, is
1418
1. Kirschner et al. / First experiments
d e t e r m i n e d solely by the p r o p e r t i e s s u p e r c o n d u c t o r s applied.
of
3. F A B R I C A T I O N OF STRUCTURAL ELEMENTS The m a t e r i a l of the rings consists of an Y I B a 2 C u 3 0 7 _ x s u p e r c o n d u c t i n g compound, which was prepared by the usual method (grindings, homogenizing, heat t r e a t m e n t s and pressing) starting from the proper mixture of Y^0~, BaC0~ and Cu0. For getting c o m p a c t ~ a ~ d m e c h a n i c a l l y stable samples we applied a pressure of 100 MPa, r e s u l t i n g a s u p e r c o n d u c t i n g ~ m a t e r i a l having a density of 4.81 g/cm ~. The samples prepared for the different experiments had critical t e m p e r a t u r e s between 87-90 K. For the c o n t i n u o u s l y p e r f o r m e d experiments the rings compressed at different occasions had outer and inner diameter of 4.6-5.0 cm and 2.2-2.4 cm respectively, while the thickness was in the range of 0.3-0.5 cm (Fig.2). Rod shape samples made of the same material and using the same t e c h n o l o g y showed a t h e r m a l ~ e x p a n sion coefficient less than 10-D/grad. It followed from our experiences that the mechanical, electrical and magnetic properties of the samples were rather sensitive to the details of the preparation technique. 4. P A R A M E T E R S OF THE MAGNET Before a s s e m b l i n g of the magnet the rings were covered by an i n s u l a t i n g varnish serving as a surface t r e a t m e n t at the same time. On one of the surfaces of the settingup elements of the magnet there was a circular groove made for holding a soft metal ring (for example indium) to provide a liquid n i t r o g e n c i r c u l a t i o n for better cooling if needed. The energizing procedure of the rings was the following: in an external magnetic field rings cooled below the critical t e m p e r a t u r e and then the external field switched off producing a persistent supercurrent preserving the magnetic field in the rings. The experiments showed an average magnetic field of 17 0e trapped in the rings c o r r e s p o n d i n g to a s u p e r c o n d u c t i n g current of~65 A.oThis value represents a 7.8x I0 ~ A/cm ~ current density if a 2500 p e n e t r a t i o n depth is taken into account. As far as the experiments showed, the i n t e n s i t y of the trapped magnetic field depends merely on the c o m p o s i t i o n and on the p a r a m e t e r s of the m a t e r i a l d e t e r m i n e d by the p r e p a r a t i o n technique. Increasing the external magnetic field above a certain value, there is no more change in the magnetic field and in the persistent
current of the rings. The magnetic fields provided either by the individual rings or by the assembled magnet was m e a s u r e d by a t e m p e r a t u r e stabilized H a l l - p r o b e (Siemens FC-32) calibrated by proton resonance. The a r r a n g e m e n t of the rings of the magnet had a net height of 7.7 cm. The magnetic field obtained by a s o l e n o i d like c a l c u l a t i o n had a value of 212 0e well c o r r e s p o n d i n g to the m e a s u r e d value of 207 0e. At present this method seems to be a reliable way for b u i l d i n g high-T ceramic s u p e r c o n d u c t i n g magnets, c As the s u p e r c o n d u c t i v i t y is e s s e n t i a l ly a surface effect, it makes possible an efficient i m p r o v e m e n t of the ceramic s u p e r c o n d u c t i n g magnets, r e p l a c i n g this simple a r r a n g e m e n t by a more complex system of rings. This latter would consists of layers formed by c o n c e n t r i c a l l y joined rings of different size and then these layers are put on top of the others, increasing the a m p e r - t u r n s and m a g n e t i c field.
Fig.2.
A ring of the magnet
REFERENCES (I) l . K i r s c h n e r et al, IEEE Trans. Magn. 17 (1981) 1999. (2) l.Kov~cs et al, Proc. ICEC-4, p.372, Eindhoven, 1972. (3) J. B~nkuti e$ al, Prdc. MT-6, p.390, Bratislava, 1977. (4) I. K i r s c h n e r et al, Cryogenics 17 (1977) 565. (5) I. K i r s c h n e r et al, Phys.Rev. 36B (1987) 2313. (6) J.B~nkuti et al, Japan.Journ. Appl. Phys. 26-3 (1987) 1073. (7) l . K i r s c h n e r et al, Eursphys. Lett. 3 (1987) 1309.
FIRST
EXPERIMENTS
WITH
A HIGH-T
C
SUPERCONDUCTING
MAGNET
I. KIRSCHNER, M. LAMM x, T. PORJESZ, J. M~TRAI x, GY. KOV~CS, T. TRAGER x, T. K~RM~N, J. GYORGY x and G.
ZSOLT
D e p a r t m e n t for Low T e m p e r a t u r e Physics, EStvSs University, Budapest, Hungary, XCentral Research and Design Institute for Silicate Industry, Budapest, H u n g a r y
A high-T c ceramic rings,
made
superconducting
magnet
of an Y I B a 2 C u 3 0 7 _ x compound.
of c y l i n d r i c a l The magnet
shape
consisting
was
consctructed
of
of 20 i n d i v i d u a l
rings can produce a magnetic field of 0.02 T (exactly 207 0e) at a s u p e r c o n d u c t i n g current of 65 A. To avoid the problems of the J o u l e - h e a t i n g on the r e s i s t i v i t y of ohmic contacts, the magnet was supplied m a g n e t i c a l l y by a contactless, i n d u c t i v e method. In this way, the magnetic field is limited only by the s u p e r c o n d u c t i n g p a r a m e t e r s of the material.
I. I N T R O D U C T I O N The high field magnets, the high power electric energy transport and the rotating electrical machines of d i f f e r e n t kinds are very prospective areas of the a p p l i c a t i o n for the h i g h - T superconducting ceramics. Initiated o~ this basis we began planning and d e v e l o p i n g high-T suc p e r c o n d u c t i n g magnets. These i n v e s t i g a tions are based on our e x p e r i e n c e s in a n a l i t i c a l and computer aided design, b u i l d i n g and operating (1,2,3,4) of conventional s u p e r c o n d u c t i n g magnets and in basic research (5,6,7) on high-T c superconductors. In this paper we present the c o n s t r u c tion and the most important p a r a m e t e r s of a magnet, shown in Fig.l, made of 20 pieces of high-T s u p e r c o n d u c t i n g ceramic rlngs. Thls magnet was e n e r g i z e d by a contactless magnetic i n d u c t i o n method. •
.
ments. S u p p o s i n g an e x c i t a t i o n current having a nominal value of 100 A and a contact r e s i s t i v i t y of about 0.1-0.01 ohms, the d i s s i p a t e d energy is 100 W to 1 kW, being too much to be cooled.
C
2. C O N S T R U C T I O N OF THE MAGNET For planning and building of a magnet made of a rigid and brittle h i g h - T superc o n d u c t i n g ceramics we had two cholces: 1. making a c o n v e n t i o n a l solenoid and s u p p l y i n g it by the aid of a d.c. current source, 2. r e a l i z i n g a magnet d i f f e r e n t l y from the accustomed, c o n s i s t i n g of individual rings, supplying with energy by induction. The first v a r i a t i o n is backed up by usual mode of action and the easily available r e g u l a t e d current sources. The constr u c t i o n of this type of ceramic magnets seemed to be very difficult because of the contact resistances arising from the current lead to s u p e r c o n d u c t o r junctions and from the coupling of structural ele-
0921-4534/88/$03.50 © Elsevier Science Publishers B.V. (North-Holland Physics Publishing Division)
Fig.1.
Picture
of the magnet
C o n s i d e r i n g the above m e n t i o n e d cir3umstances we chose the version of the magnet of second kind, built up of individual rings and m a g n e t i c a l l y energized. In this case, using s u f f i c i e n t l y thin and stabilized rings, the upper limit of the magnetic field which can be produced, is
1418
1. Kirschner et al. / First experiments
d e t e r m i n e d solely by the p r o p e r t i e s s u p e r c o n d u c t o r s applied.
of
3. F A B R I C A T I O N OF STRUCTURAL ELEMENTS The m a t e r i a l of the rings consists of an Y I B a 2 C u 3 0 7 _ x s u p e r c o n d u c t i n g compound, which was prepared by the usual method (grindings, homogenizing, heat t r e a t m e n t s and pressing) starting from the proper mixture of Y^0~, BaC0~ and Cu0. For getting c o m p a c t ~ a ~ d m e c h a n i c a l l y stable samples we applied a pressure of 100 MPa, r e s u l t i n g a s u p e r c o n d u c t i n g ~ m a t e r i a l having a density of 4.81 g/cm ~. The samples prepared for the different experiments had critical t e m p e r a t u r e s between 87-90 K. For the c o n t i n u o u s l y p e r f o r m e d experiments the rings compressed at different occasions had outer and inner diameter of 4.6-5.0 cm and 2.2-2.4 cm respectively, while the thickness was in the range of 0.3-0.5 cm (Fig.2). Rod shape samples made of the same material and using the same t e c h n o l o g y showed a t h e r m a l ~ e x p a n sion coefficient less than 10-D/grad. It followed from our experiences that the mechanical, electrical and magnetic properties of the samples were rather sensitive to the details of the preparation technique. 4. P A R A M E T E R S OF THE MAGNET Before a s s e m b l i n g of the magnet the rings were covered by an i n s u l a t i n g varnish serving as a surface t r e a t m e n t at the same time. On one of the surfaces of the settingup elements of the magnet there was a circular groove made for holding a soft metal ring (for example indium) to provide a liquid n i t r o g e n c i r c u l a t i o n for better cooling if needed. The energizing procedure of the rings was the following: in an external magnetic field rings cooled below the critical t e m p e r a t u r e and then the external field switched off producing a persistent supercurrent preserving the magnetic field in the rings. The experiments showed an average magnetic field of 17 0e trapped in the rings c o r r e s p o n d i n g to a s u p e r c o n d u c t i n g current of~65 A.oThis value represents a 7.8x I0 ~ A/cm ~ current density if a 2500 p e n e t r a t i o n depth is taken into account. As far as the experiments showed, the i n t e n s i t y of the trapped magnetic field depends merely on the c o m p o s i t i o n and on the p a r a m e t e r s of the m a t e r i a l d e t e r m i n e d by the p r e p a r a t i o n technique. Increasing the external magnetic field above a certain value, there is no more change in the magnetic field and in the persistent
current of the rings. The magnetic fields provided either by the individual rings or by the assembled magnet was m e a s u r e d by a t e m p e r a t u r e stabilized H a l l - p r o b e (Siemens FC-32) calibrated by proton resonance. The a r r a n g e m e n t of the rings of the magnet had a net height of 7.7 cm. The magnetic field obtained by a s o l e n o i d like c a l c u l a t i o n had a value of 212 0e well c o r r e s p o n d i n g to the m e a s u r e d value of 207 0e. At present this method seems to be a reliable way for b u i l d i n g high-T ceramic s u p e r c o n d u c t i n g magnets, c As the s u p e r c o n d u c t i v i t y is e s s e n t i a l ly a surface effect, it makes possible an efficient i m p r o v e m e n t of the ceramic s u p e r c o n d u c t i n g magnets, r e p l a c i n g this simple a r r a n g e m e n t by a more complex system of rings. This latter would consists of layers formed by c o n c e n t r i c a l l y joined rings of different size and then these layers are put on top of the others, increasing the a m p e r - t u r n s and m a g n e t i c field.
Fig.2.
A ring of the magnet
REFERENCES (I) l . K i r s c h n e r et al, IEEE Trans. Magn. 17 (1981) 1999. (2) l.Kov~cs et al, Proc. ICEC-4, p.372, Eindhoven, 1972. (3) J. B~nkuti e$ al, Prdc. MT-6, p.390, Bratislava, 1977. (4) I. K i r s c h n e r et al, Cryogenics 17 (1977) 565. (5) I. K i r s c h n e r et al, Phys.Rev. 36B (1987) 2313. (6) J.B~nkuti et al, Japan.Journ. Appl. Phys. 26-3 (1987) 1073. (7) l . K i r s c h n e r et al, Eursphys. Lett. 3 (1987) 1309.