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FERROMAGNETIC INSERTS INCREASING THE FIELD OF A SOLENOID
P. Genevey, G. Neyret, A. Sagniez, B. Turck
To cite this version:
P. Genevey, G. Neyret, A. Sagniez, B. Turck. FERROMAGNETIC INSERTS INCREASING THE FIELD OF A SOLENOID. Journal de Physique Colloques, 1984, 45 (C1), pp.C1-817-C1-820.
�10.1051/jphyscol:19841167�. �jpa-00223641�
JOURNAL DE PHYSIQUE
Colloque C1, suppl6ment a u n o 1, Tome 45, janvier 1984 page C1-817
FERROMAGNETIC INSERTS INCREASING THE F I E L D OF A SOLENOID
P . Genevey, G . Neyret, A . Sagniez and B . Turck
C. E. A. /Saclay, DPhPE/STIPE, 91 191 Gif-sur-Yvette Cedex, France
Resume
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Durant l e s 1 0 d e r n i e r e s annees, de nombreuses s t a t i o n s d ' e s s a i s p r o - m t des i n d u c t i o n s de 7 & 8 T o n t 6 t 6 c o n s t r u i t e s . Le d6beloppement a c t u e ldes machines s u p r a c o n d u c t r i c e s n 6 c e s s i t e des c a r a c t 6 r i s a t i o n s d 1 6 c h a n t i l l o n s dans des i n d u c t i o n s de 9 & 1 0 T . L ' u t i l i s a t i o n de deux p 6 l e s f e r r o m a g n e t i q u e s permet d ' o b t e n i r simplement un accroissement de 2 Teslas de l ' i n d u c t i o n dans l l e n t : r e f e r . Cet. accroissement d6pend du mat6riau, de l a longueur de l ' e n t r e f e r e t du d i a m e t r e des p 6 l e s . N o t r e d i s p o s i t i f e x p e r i m e n t a l c o n s i s t e en deux p d l e s c y l i n d r i q u e s en a l l i a g e f e r
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25% C o b a l t de 149 mm de d i a m e t r e e t de 20 mm d ' e n t r e f e r . L ' i n d u c t i o n maximale e s t a i n s i augment6e de 7 , 2 & 9,2 T. Ce d i s - p o s i t i f permet de mesurer deux 6 c h a n t i l l o n s en forme d 1 6 p i n g 1 e k cheveux sans a v o i r k r 6 c h a u f f e r l e s o l 6 n o i d e au moment des changements d 8 6 c h a n t i l l o n s . A b s t r a c t-
D u r i n g t h e l a s t t e n years, l o t s o f t e s t f a c i l i t i e s p r o v i d i n g f i e l d s up t o 7 o r 8 T have been b u i l t . The p r e s e n t development o f s u p e r c o n d u c t i n g devices needs s h o r t sample measurement i n f i e l d up t o 9 o r 1 0 T. The use o f 2 f e r r o m a g n e t i c i n s e r t s i n t h e b o r e o f t h e s o l e n o i d a l l o w s a cheap, s i m p l e and r e l i a b l e i n c r e a s e o f t h e f i e l d i n t h e gap up t o 2 T. T h i s i n c r e a s e depends on t h e used m a t e r i a l , t h e w i d t h o f t h e gap and t h e diameter o f t h e i n s e r t s . Our system c o n s i s t s o f a s e t o f two c y l i n d r i c p i e c e s o f a 25% C o b a l t a l l o y , 149 mm i n d i a m e t e r p r o v i d i n g a 1 0 mm gap, w i c h r e s u l t s i n a i n c r e a s e of t h e f i e l d i n a 1 9 0 mm u s e f u l b o r e c o i l , f r o m 7.2 t o 9.2 T. The so m o d i f i e d c o i l a l l o w s two h a i r p i n samples t o be measured i n t h e same r u n . xI n most l a b o r a t o r i e s , s u p e r c o n d u c t i n g magnet ( b u b b l e chamber, a c c e l e r a t o r magnets) have been g e n e r a l l y designed t o g e n e r a t e f i e l d s up t o 7 T. The t e s t f a c i l i t i e s have been designed a c c o r d i n g l y t o q u a l i f y c o n d u c t o r b y s h o r t sample t e s t s i n t h e f i e l d range. F u s i o n programs (Tore Supra, M F T F) r e q u i r e magnets w o r k i n g a t 9 T. o r more.
The c o n s t r u c t i o n o f t e s t f a c i l i t i e s i n t h i s range i s expensive. I t seems i n t e r e s t i n g t o use a v a i l a b l e t e s t f a c i l i t i e s b y i n t r o d u c i n g f e r r o m a g n e t i c c o n c e n t r a t o r s t o i n - crease t h e f i e l d i n a gap where t h e s h o r t sample i s l o c a t e d .
The p o s s i b i l i t y t o i n c r e a s e t h e magnetic f i e l d s by f e r r o m a g n e t i c c o n c e n t r a t o r s i s w e l l known b u t has seldom been used a t l i q u i d h e l i u m t e m p e r a t u r e / I / . U s i n g two i r o n c o b a l t a l l o y b l o c k s p u t i n t h e i n n e r p a r t o f a s o l e n o i d , we have i n c r e a s e d f i e l d f r o m 7.2 t o 9.2 T i n a 20 mm gap.
A s i m p l e t h e o r y shows t h a t , f o r t w o i n d e n t i c a l f l a t p o l e s u n i f o r m e l y magnetized a l o n g t h e a x i s o f symmetry, t h e magnetic f i e l d i n t h e m i d d l e o f t h e gap between t h e two p o l e s can be enhanced b y n B .
x Work s u p p o r t e d by t h e A s s o c i a t i o n Euratom
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CEA.Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:19841167
C1-818 JOURNAL DE PHYSIQUE
Where M i s t h e magnetization of t h e material (2.1 T f o r a f u l l y s a t u r a t e d iron and 2.4 T f o r a f u l l y s a t u r a t e d iron-cobalt a l l o y ) Q and Q a r e shown on f i g u r e 1.
2
Figure 1
This value give a good approximation of t h e f i e l d enhancement. The main characte- r i s t i c of t h e solenoid of t h e t e s t f a c i l i t y /2/ a r e given in t a b l e helow :
Useful i n t e r n a l diameter
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206 mmi n t e r n a l diameter
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220 mmWinding external diameter
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300 mmlength
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380 mmCentral f i e l d
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7.2 TA c r y o s t a t i s i n s e r t e d i n t h e bore of t h e solenoid which allows t o introduce and remove t h e t e s t assembly ( s e e f i g . 2, photo 1) ( 3 c u r r e n t l e a d s , 2 ferromagnetic blocks, 2 s h o r t samples) without warming up and recooling t h e c o i l . I t s useful a p e r t u r e i s 189 mm.
Figure 2
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Test assembly Photo 1-
Test assembly 1 : solenoid-
2 : i n s e r t e d c r y o s t a t-
3-4 : lower, upper block-
5 : wedge
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6 : sample holder-
7 : sample-
8 : support.The magnetic m a t e r i a l i s an i r o n - c o b a l t a l l o y (AFK1 f r o m Metalimphy). I t s composi- t i o n i s : i r o n 74.2 %, c o b a l t 25 %, chromium 0.3 %,manganese 0.5 %. When f u l l y s a t u - r a t e d i t s m a g n e t i z a t i o n i s 2.4 T.
I n o u r system, t h e upper b l o c k i s n o t e x a c t l y a x i s y m m e t r i c a l t o p r o v i d e room f o r t h e sample h o l d e r i t s e l f . The diameter o f t h e b l o c k s i s 149 mm. The f i e l d has been c a l c u l a t e d b y a computer code. The depth o f t h e gap has been choosen t o o b t a i n t h e 2 T enhancement and t h e b e s t f i e l d homogeneity i n t h e p l a n e where t h e sample t o be measured i s l o c a t e d . F i g u r e 3 g i v e s t h e f i e l d homogeneity B ( x )
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B ( 0 ) along t h eR i n )
conductor a x i s , f o r a gap depth o f 20 mm (B ( 0 ) b e i n g t h e field-0;-the a x i s and B ( x ) t h e v e r t i c a l component a t a d i s t a n c e x f r o m t h e a x i s ) . I n t h e u s e f u l p a r t x 2.5 cm t h e f i e l d homogeneity w i t h t h e f e r r o m a g n e t i c i n s e r t i s t h e same as t h e one w i t h o u t . The use o f shims can improve t h i s homogeneity i f needed.
F i g u r e 3 : f i e l d homogeneity F i g u r e 4 : m a g n e t i c f i e l d 1
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w i t h o u t i n s e r t2
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w i t h i n s e r t1
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w i t h o u t i n s e r t 2-
w i t h i n s e r tThe f i e l d has been measured b y a s m a l l i n t e g r a t i n g c o i l and an i n t e g r a t o r v o l t m e t e r w i t h a low d r i f t ( p h o t o 2 ) . The d e v i c e has been c a l i b r a t e d u s i n g c o i l s whose f i e l d have been c a l i b r a t e d b y N.M.R. The v a l u e o f t h e f i e l d i n t h e m i d p l a n e i s g i v e n i n f i g u r e 4. The p r e c i s i o n on t h e f i e l d i s b e t t e r t h a n 5 10-4. One p r o b l e m i s t h e remanent f i e l d Br, s i n c e i n t e g r a t i n g method can o n l y measure t h e f i e l d v a r i a t i o n s and n o t t h e a b s o l u t e v a l u e . We have observed t h a t B r i s t h e same a t 4.2 K and a t room t e m p e r a t u r e and does n o t v a r y when t h e two b l o c k s are t a k e n a p a r t and p u t again t o g e t h e r i n o r d e r t o change t h e sample. The B r v a l u e w i t h a 20 mm gap i s 0.004 T. I n a 9 T f i e l d such an e r r o r becomes n e g l i g i b l e .
C1-820 JOURNAL DE PHYSIQUE
Photo 2 : sample h o l d e r
Another problem a r i s e s f r o m t h e magnetic f o r c e s when t h e i n s e r t i s n o t e x a c t l y a t t h e m a g n e t i c c e n t e r . The i n s e r t i s f i r s t p u t a l i t t l e l o w e r t h a n t h e m a g n e t i c c e n t e r w i t h i t s mechanical s u p p o r t b e i n g f r e e t o move. When i n c r e a s i n g t h e f i e l d t h e i n s e r t moves up t o t h e good p o s i t i o n , t h e n t h e s u p p o r t i s clamped.
A sample h o l d e r a l l o w s t w o h a i r p i n samples t o b e measured i n t h e same r u n . Two samples o f t h e " t o r e supra" c o n d u c t o r have been measured i n t h e 10 T t e s t f a c i l i t y and t h e n i n t h i s (7 + 2) T f a c i l i t y . The r e s u l t s a r e i d e n t i c a l . ( c o n d u c t o r : 2.8 x 5.6 mm2, c r i t i c a l c u r r e n t a t 9 T and 4.2 K : 1400 A.).
As f a r as t h e s h o r t sample measurements a r e concerned t h i s t e c h n i q u e a l l o w s t o i n c r e a s e t h e magnetic f i e l d o f a t e s t f a c i l i t y b y about 2 t e ~ l a s a v o i d i n g t h e use o f an i n s e r t c o i l which decreases t h e u s e f u l b o r e ' o f t h e t e s t f a c i l i t y .
REFERENCES :
1
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I. R u z i c k a and M. L i t o m i s k y . Les champs magnetiques i n t e n s e s , l e u r p r o d u c t i o n e t l e u r a p p l i c a t i o n .Grenoble Sept. 66 p. 1 2 1 (C.N.R.S.)
2
