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Submitted on 1 Jan 1984
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ELECTRICAL JOINTS FOR THE EUROPEAN LCT COIL
C. Albrecht, H. Marsing, H. Neumüller
To cite this version:
C. Albrecht, H. Marsing, H. Neumüller. ELECTRICAL JOINTS FOR THE EUROPEAN LCT COIL.
Journal de Physique Colloques, 1984, 45 (C1), pp.C1-607-C1-610. �10.1051/jphyscol:19841123�. �jpa- 00223593�
E L E C T R I C A L J O I N T S FOR THE EUROPEAN L C T C O I L
C. A l b r e c h t , H. Marsing and H.W. Neumiiller
Siemens AG, Research Laboratories, 0-8520 Erlangen, F . R. G .
RQsumL: Une d e s c r i p t i o n e s t donnee d l u n r a c c o r d b r a s & - r e t r e i n t d e c o n s t i t u t i o n segment6e pour 1 5 kA s o u s 1 t e s l a a i n s i que d e l ' a p p a r e i l l a g e d e mesure i n d u c t i v e . Une u n i t & de 4 segments e s t longue d e 160 mm e t p r 6 s e n t e une r e s i s t a n c e Q l e c t r i q u e d e 2,3 .10-1052 pour 1 T. La r e s i s t a n c e d ' u n r a c c o r d p r o t o t y p e a 6 t B mesurBe j u s q u ' d 5 T. Des c y c l e s thermiques e n t r e 77 K e t 300 K n ' o n t e x e r c 6 aucune i n f l u e n c e s u r l a r 6 s i s t a n c e . La r e p r o d u c t i b i l i t e en f a b r i c a t i o n a e t 6 v 8 r i f i e e .
A b s t r a c t : A d e s c r i p t i o n i s g i v e n of a s o l d e r - p r e s s j o i n t of segmented d e s i g n f o r 1 5 kA a t 1 T e s l a , a s w e l l a s o f i n d u c t i v e measuring a p p a r a t u s . One &segment u n i t i s 160 mm i n l e n g t h and e x h i b i t s an e l e c t r i c a l r e s i s t a n c e of 2.3 . 10-10 52 a t 1 T.
R e s i s t a n c e of a p r o t o t y p e j o i n t was measured up t o 5 T. Thermal c y c l e s between 7 7 K and 300 K d i d n o t a f f e c t t h e r e s i s t a n c e . R e p r o d u c i b i l i t y of f a b r i c a t i o n h a s been proved.
I n t r o d u c t i o n
The aim was t o d e v e l o p a j o i n t d e s i g n f o r t h e e l e c t r i c a l j o i n t s of t h e LCT c o i l which e x h i b i t s b o t h good e l e c t r i c a l and m e c h a n i c a l p r o p e r t i e s and which c a n be manu- f a c t u r e d a s s i m p l y a s p o s s i b l e . A compact c o n s t r u c t i o n was a l s o r e q u i r e d t o f i t each j o i n t i n a vacuum-tight h o u s i n g of h i g h d i e l e c t r i c s t r e n g t h (12 kV DC). E x p e r i m e n t a l i n v e s t i g a t i o n s showed t h a t a combination of s o l d e r i n g and m e c h a n i c a l p r e s s u r e pro- duced t h e most f a v o u r a b l e r e s u l t s . T h i s s o l d e r - p r e s s j o i n t g u a r a n t e e d a r e p r o d u c i b l e and r e l i a b l e f a b r i c a t i o n f o r t h e complex d e s i g n of t h e LCT c o n d u c t o r which i s c o o l e d by subcooled l i q u i d h e l i u m / I / . The c o n c e p t a l s o f u l l f i l l s t h e r e q u i r e m e n t s f o r minimum h e a t d i s s i p a t i o n , h i g h m e c h a n i c a l s t r e n g t h and r e s i s t a n c e t o t h e r m a l a g i n g . Each of t h e 1 3 j o i n t s i s d i v i d e d i n t o s e v e r a l s e g m e n t s , which c a n be p r e a s s e m b l e d and mounted w i t h o u t m o d i f i c a t i o n s i n t h e c o n d u c t o r s t r u c t u r e . The j o i n t d e s i g n , t h e e l e c t r i c a l p r o p e r t i e s of a p r o t o t y p e j o i n t and t h e i n d u c t i v e c u r r e n t a p p a r a t u s , p r o v i d i n g c u r r e n t s up t o 1 6 kA a r e d e s c r i b e d .
J o i n t d e s i g n
The d e s i g n of a j o i n t , a s i n s t a l l e d i n t h e LCT c o i l i s shown i n F i g . 1. Compared t o t h e p r o t o t y p e j o i n t , i t i s m e r e l y s h o r t e n e d by one segment. The c u r r e n t t r a n s f e r i s accomplished by 18 s u p e r c o n d u c t i n g N b T i - m u l t i f i l a m e n t c r o s s c o n n e c t i o n c o n d u c t o r s ( c c ) , which a r e p r e s s e d a g a i n s t t h e LCT c o n d u c t o r s u r f a c e s by a n a r r a n g e m e n t of sev- e r a l p r e s s u r e and s u p p o r t i n g e l e m e n t s . The o u t e r s u p p o r t i n g r i n g was made of alumi- nium, which p r o d u c e s a d d i t i o n a l p r e s s u r e on t h e c o n t a c t a r e a s due t o t h e d i f f e r e n t t h e r m a l s h r i n k i n g a f t e r c o o l i n g down t o 4.2 K. The i n d i v i d u a l segments were s o l d e r e d t o t h e LCT c o n d u c t o r ends u s i n g a n Ag4Sn s o l d e r . The c o m p l e t e l y assembled j o i n t i s surrounded by a h e l i u m - t i g h t h o u s i n g . G l a s s - f i b r e epoxy (GFE) d i s c s between t h e segments and b o r e s n e a r t h e c o n n e c t i o n a r e a s conduct t h e h e l i u m f l o w which l e a v e s t h e c o n d u c t o r ends and t h e n p a s s e s i n t o t h e helium o u t l e t s a t t h e t o p of t h e h o u s i n g . A l l 1 3 c o n n e c t i o n s a r e a r r a n g e d w i t h i n t h e s u p p l y dome of t h e LCT magnet ( F i g . 2 ) . D i v i s i o n i n t o segments h a s t h e a d v a n t a g e t h a t a u n i f o r m compression a t t h e c o n t a c t f a c e s of t h e c o n d u c t o r s c a n be a c h i e v e d d e s p i t e t h e t o l e r a n c e s i n t h e dimensions o f t h e LCT c o n d u c t o r s u r f a c e s . The arrangement of t h e CC on b o t h f l a t s i d e s of t h e LCT
Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:19841123
C1-608 JOURNAL DE PHYSIQUE
c o n d u c t o r g u a r a n t e e s t h a t each s i n g l e s t r a n d i s connected w i t h t h e same a r e a i n d e - p e n d e n t of t h e s t r a n d p i t c h . The most i m p o r t a n t d a t a of t h e LCT c o n d u c t o r and CC a r e l i s t e d i n T a b l e I. F i g s . 3a13b show t h e c r o s s - s e c t i o n s .
Table I: Conductor c h a r a c t e r i s t i c s
LC1 c o n d u c t o r : F l a t c a b l e o f 23 s t r a n d s s o l - S i n g l e s t r a n d Dimensions 2.35 x 5.1 mm2
d e r e d on a Vacromium c o r e T w i s t p i t c h 30 mm
Dimensions 7.4 x 38.5 mm2 M a t r i x Cu, oc = 4.7
S t r a n d p i t c h 400 mm I, (4.2 K ) 1500 A / ~ T /I/
c r o s s c o n n e c t i o n T w i s t p i t c h 50 mm
conductor: Type F1250-15 (VRC) M a t r i x Cu,oc= 1.5
Dimensions 1.8 x 3.6 mmz 1, (4.2 K ) 1500 A/5T
E x p e r i m e n t a l s e t - u p
The whole assembly w i t h p r o t o t y p e j o i n t i s shown i n F i g . 4 , ( s e e T a b l e I1 f o r d a t a ) . A LCT c o n d u c t o r loop w i t h o u t s t a i n l e s s s t e e l c o n d u i t , s h o r t - c i r c u i t e d by t h e t e s t j o i n t forms t h e s e c o n d a r y l o o p of a s u p e r c o n d u c t i n g t r a n s f o r m e r . The s u p e r c o n d u c t - i n g p r i m a r y c o i l i s l o c a t e d i n t h e c e n t e r of t h e a p p a r a t u s .
Table 11: Data o f t h e i n d u c t i v e c u r r e n t a p p a r a t u s and t h e L C T j o i n t
Primary c o i l : O u t e r d i a . 146 mm Secondary l o o p : Outer dia. 307 mm
Windings 2912 I n d u c t a n c e 7.7 x loe7 H
I n d u c t a n c e 1.12 H M u t u a l
I1 (max.) 70 A i n d u c t i o n 1.75 x H
LCT j o i n t : J o i n t a r e a / RRR (copper) 1 0 0
segment 1540 mm" J o i n t r e s i s t a n c e
Segment l e n g t h 40 mm (4-segments) 2.3 x 5211 T
According t o t h e ramp r a t e o f t h e p r i m a r y c u r r e n t 1 1 , t h e c u r r e n t I t h r o u g h t h e j o i n t i s I = ~ ~ ~ ( l - e - t f ~ ) / R , where T = L/R; T : time c o n s t a n t , L: i n d u c t a n c e of t h e LCT l o o p , M: m u t u a l i n d u c t a n c e .
S i n c e 11 = I1.t and 7 i s v e r y l a r g e : I = M . I l l L = 2 2 7 . I1 i f i l > 0.5 A / S . The i n i t i a l s t a t e I = 0 i s a c h i e v e d by a h e a t e r winding on t h e LCT l o o p .
The j o i n t was mounted w i t h i n t h e b o r e of a 6T magnet 121. The whole p r o t o t y p e assem- b l y was c o o l e d b y l i q u i d h e l i u m (T = 4.2 K ) . The c u r r e n t I was d e t e r m i n e d by meas- u r i n g t h e s e l f - f i e l d u s i n g two H a l l p r o b e s , one s i t u a t e d on each s i d e of t h e LCT c o n d u c t o r . Before t h e j o i n t was assembled a d i r e c t c a l i b r a t i o n was performed f e e d - i n g c u r r e n t ( G 6 0 0 0 A) i n t h e c o n d u c t o r ends and t h e n e x t r a p o l a t i n g t h e c a l i b r a t i o n c u r v e t o h i g h e r c u r r e n t s .
R e s u l t s and D i s c u s s i o n
The j o i n t r e s i s t a n c e s R were d e t e r m i n e d by t h e time c o n s t a n t 7 of t h e c o n d u c t o r l o o p . 7 was measured a t v a r i o u s t i m e s i n o r d e r t o r e g i s t e r a p o s s i b l e dependence of t h e j o i n t r e s i s t a n c e on t r a n s p o r t c u r r e n t 131. The i n d u c t a n c e of t h e s e c o n d a r y l o o p was measured t o w i t h i n 2 1 0 %, R t o w i t h i n + 16%.
The measured v a l u e s of t h e two H a l l p r o b e s a r e n e a r l y i d e n t i c a l . T h e r e f o r e , a homo- geneous c u r r e n t d i s t r i b u t i o n c a n be assumed w i t h i n t h e LCT c o n d u c t o r c r o s s - s e c t i o n , the'more s o s i n c e t h e c a l c u l a t e d s e l f - f i e l d s a g r e e w i t h t h e measured o n e s t o w i t h i n a few p e r c e n t . The e x p e r i m e n q a l r e s u l t s f o r 5 segments and 3 segments i n F i g . 5 show t h a t t h e c u r r e n t i s a l s o homogeneously d i s t r i b u t e d o v e r t h e i n d i v i d u a l segments of t h e j o i n t . y o r e o v e r , 50 q u i c k c y c l e s (300 K 178 K / 300 X) d i d n o t a f f e c t t h e e l e c t r i c a l p r o p e r t i e s . The j o i n t r e s i s t a n c e was found t o b e i n d e p e n d e n t of c u r r e n t w i t h i n t h e measuring a c c u r a c y . Obviously o n l y t h e p e r i p h e r a l f i l a m e n t s c a r r y t h e
The measured r e s i s t a n c e c o u l d b e d i v i d e d i n t o a f i e l d - d e p e n d e n t / 4 / c o n t r i b u t i o n due t o t h e c o p p e r and i n t o t h e j o i n t i n t e r f a c e ( s o l d e r and c o n t a c t ) r e s i s t a n c e . These two c o n t r i b u t i o n s a r e d e s c r i b e d by t h e q u a r i t i t y pal ( p s p e c i f i c r e s i s t i v i t y ; 1 c h a r a c t e r i s t i c l e n g t h i n t h e d i r e c t i o n of c u r r e n t t r a n s f e r ) . ( p . 1 ) ~ ~ = 4 * 10-9S2cm2 was found f o r t h e c o n t r i b u t i o n of c o p p e r f o r B 3 0 and ( p . 1 ) ~ = 3.4 . 10-9S2 cm2 f o r t h e i n t e r f a c e r e s i s t a n c e , t h e l a t t e r b e i n g comparable t o r e s u l t s i n l i t e r a t u r e 131.
Using t h e s p e c i f i c r e s i s t i v i t y of c o p p e r , 1 i s 3.5 t i m e s a s h i g h a s t h e mean t h i c k n e s s of t h e copper s u r f a c e l a y e r . T h i s e n l a r g e d r e s i s t a n c e c o u l d be e x p l a i n e d by a f i e l d - d e p e n d e n t c o n t a c t r e s i s t a n c e of t h e NbTi copper i n t e r f a c e s o r by t h e i n - c r e a s e d e f f e c t i v e l e n g t h i n c u r r e n t t r a n s f e r . The l a t t e r c o u l d b e due t o t h e j o i n t geometry and t o t h e t w i s t p i t c h of CC which i s a b o u t 25 % g r e a t e r t h a n t h e w i d t h of a LCT c o n d u c t o r .
C o n c l u s i o n
The m e c h a n i c a l c o n c e p t of t h e c o n t a c t d e s i g n h a s been proved w i t h t h e assembly of t h e 1 3 j o i n t s i n t h e LCT c o i l . The j o i n t s a l l o w a r e p r o d u c i b l e m a n u f a c t u r e w i t h i n c l o s e l i m i t s . The LCT c o i l w i l l be t e s t e d a t K a r l s r u h e towards t h e end of 1983.
R e f e r e n c e s , Acknowledgment /1/ SCHMIDT C., IEEE Trans. Mag. 1 9 No. 3 (1983) 707 -
121 NEUMULLER H.-W., IEEE Trans. Mag. 1 7 No. 5 ( 1 9 8 1 ) 2274
/ 3 / GOODRICH L.F. and Ekin J.W., IEEE T & n s . ~ a ~ . 1 7 No. 1 (1981) 69 / 4 / FICKETT F.R., Proc. MT-4 Brookhaven (1972) 5 3 F
The j o i n t d e s c r i b e d i s a p p l i e d i n t h e LCT EURATOM c o i l , m a n u f a c t u r e d by Siemens u n d e r KfK c o n t r a c t No. 130/D1/427.841 ( ~ e r n f ~ r s c h u n ~ s z e n t r u m K a r l s r u h e ) .
LCT conductors Helium /Q
( c o n d u i t removed)
Pressure plater -'
Screw plater
F i g . 1: Design of t h e LCT j o i n t F i g . 2: Connector h o u s i n g s w i t h LCT j o i n t s i n s i d e d u r i n g LCT c o i l assembly.
C1-610 JOURNAL DE PHYSIQUE
Fig. 3a: Cross connection conductor Fig. 3b: LCT conductor with con-
F 1250-15 duit removed (section)
Fig. 5: Joint resistance as a function of applied magnetic field
f
0 5-regment contact
1 2 o 5-segment contact (prototype)
1
[ copper resinanre lfhermally cycled,
1
3-segment contact fextrapolatedl
--- _--_-_______
joint interface resistance
