GENERAL DESIGN AND CONDUCTOR STUDY FOR THE "ALEPH" SUPERCONDUCTING SOLENOID

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GENERAL DESIGN AND CONDUCTOR STUDY FOR THE ”ALEPH” SUPERCONDUCTING

SOLENOID

H. Desportes, J. Le Bars, C. Meuris

To cite this version:

H. Desportes, J. Le Bars, C. Meuris. GENERAL DESIGN AND CONDUCTOR STUDY FOR THE

”ALEPH” SUPERCONDUCTING SOLENOID. Journal de Physique Colloques, 1984, 45 (C1), pp.C1- 341-C1-345. �10.1051/jphyscol:1984170�. �jpa-00223726�

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JOURNAL DE PHYSIQUE

Colloque C1, suppl6rnent au no 1, Tome 45, janvier 1984 page C1-341

GENERAL DESXGN AND CONDUCTOR STUDY FOR THE "ALEPH" SUPERCONDUCTING

SOLENOID

H . Desportes, J. L e Bars and C . Meuris

C . E. N . -SacZay, STIPE, 9 1 191 Gif-sup-Yvette Cedez, France

R6sum6 - Un t r e s l a r g e s o l 6 n o i d e supraconducteur e s t en c o u r s d 1 6 t u d e p o u r l e d 6 t e c t e u r ALEPH d e s t i n 6 au LEP. La c o n c e p t i o n g6nPrale e s t brievement d 6 c r i t e a i n s i que l e s e s s a i s de q u a l i f i c a t i o n du conducteur s t a b i l i s 6 i 1 'a l u m i n i u m en c o u r s de developpement pour c e t aimant.

A b s t r a c t - A l a r g e s u p e r c o n d u c t i n g s o l e n o i d i s b e i n g d e s i g n e d f o r t h e LEP d e t e c t o r ALEPH. The general d e s i g n i s b r i e f l y d e s c r i b e d as w e l l as q u a l i f i c a t i o n t e s t s f o r t h e A l u - s t a b i l i z e d c o n d u c t o r under development f o r t h i s magnet.

I

-

INTRODUCTION

A l a r g e s u p e r c o n d u c t i ~ s o l e n o i d ( f r e e b o r e 5 m i n d i a m e t e r and 7 m l o n g ) i s under d e s i g n f o r t h e ALEPH d e t e c t o r scheduled t o be i n s t a l l e d on t h e LEP c o l l i d e r a t CERN i n 1987.

The S o l e n o i d i s surrounded b y a 2 600 t l a m i n a t e d i r o n yoke and must produce t o g e t h e r w i t h t h e yoke a f i e l d o f 1. 5 T w i t h a h i g h f i e l d u n i f o r m i t y o v e r t h e l a r g e volume o f t h e c e n t r a l d e t e c t o r . A schematic s k e t c h o f t h e whole magnet j s shown i n F i g 1.

The p r e s e n t s t a t u s o f t h e s o l e n o i d , c o n t r a c t e d b y CERN on b e h a l f o f t h e ALEPH european c o l l a b o r a t i o n t o t h e CEN SACLAY, i s concerned w i t h t h e d e s i g n and e n g i n e e r i n g stage, w i n d i n g method e l a b o r a t i o n and c o n d u c t o r development.

F i g 1 - Schematic s k e t c h o f t h e

A L E P H D e t e c t o r

2

-

GENERAL DESIGN

A t t h e p r e s e n t stage, t h e main parameters o f t h e c o i l system a r e t h o s e i n d i c a t e d i n T a b l e 1.

The w i n d i n g c o n s i s t s o f a m a i n , u n i f o r m e l y wound s o l e n o i d , 6. 4 m lorlg, and two compensating c o i l s a t b o t h ends, needed f o r f i e l d homogeneity a d j u s t m e n t . The t h r e e c o i l s a r e c l o s e l y f i t t e d and p o t t e d i n t o a common s t r u c t u r a l member, made of a t h i c k A l u - a l l o y c y l i n d e r , which serves as a mandrel f o r l a y i n g t h e c o n d u c t o r ( i n s i d e w i n d i n g f o r t h e main s o l e n o i d , o u t s i d e w i n d i n g f o r t h e compensating c o i l s ) , and as t h e hoop r e s t r a i n i n g s t r u c t u r e .

Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:1984170

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C1-342 JOURNAL DE PHYSIQUE

C o o l i n g o f t h e s o l e n o i d i s c a r r i e d o u t b y c i r c u l a t i n g 2 phase Helium i n an a r r a y o f p i p e s welded on t h e s t r u c t u r a l c y l i n d e r and f e d f r o m a 300 W r e f r i - g e r a t o r . I n o r d e r t o make p o s s i b l e t h e t r a n s p o r t o f t h e s o l e n o i d t o CERN, i t has been necessary t o d i v i d e i t i n t o two h a l v e s , i n d i v i d u a l l y assembled i n h a l f - c r y o s t a t s , which can be e a s i l y re-connected t o g e t h e r a t t h e e x p e r i m e n t s i t e .

The whole c o n s t r u c t i o n o f t h e s o l e n o i d and o f i t s c r y o s t a t i s made o f Alu-based m a t e r i a l i n o r d e r t o m i n i m i z e t h e w e i g h t and t h e N u c l e a r a b s o r p t i o n t h i c k n e s s seen b y emerging p a r t i c l e s .

The c o i l s t r u c t u r e i s shown s c h e m a t i c a l l y i n F i g 2

TABLE 1

C r y o s t a t i n n e r b o r e C r y o s t a t o u t e r d i a m e t e r C r y o s t a t o v e r a l l l e n g t h Winding l e n g t h

Amp x t u r n s Nominal c u r r e n t C e n t r a l F i e l d S t o r e d Energy T o t a l w e i g h t

F i g 2 - C o i l s t r u c t u r e

3 - CONDUCTOR DESIGN

S p e c i a l a t t e n t i o n has been g i v e n t o t h e development o f an adequate A l u - s t a b i l i z e d c o n d u c t o r w e l l adapted t o t h e chosen i n d i r e c t c o o l i n g scheme.

Aluminium s t a b i l i z a t i o n t a k e s advantage o f t h e l o w r e s i s t i v i t y and h i g h thermal c o n d u c t i v i t y of h i g h p u r i t y Aluminium, t o g e t h e r w i t h l i g h t w e i g h t and s o f t mecha- n i c a l p r o p e r t i e s making i t easy t o wind. I t has been s u c e s s f u l l y used f o r t h e C e l l o magnet and i s adopted f o r s e v e r a l s o l e n o i d s under c o n s t r u c t i o n i n JAPAN.

I n t h e p r e s e n t case, due t o s a f e t y ' c o n s ~ d e r a t i o n s w i t h re g a r d t o t h e v e r y l a r g e s i z e o f t h e s o l e n o i d , a much l a r g e r c o n d u c t o r i s needed and s p e c i a l measures have t o be t a k e n f o r e n s u r i n g a h i g h q u a l i t y and f u l l l e n g t h r e l i a b i l i t y o f t h e manufactured c o n d u c t o r . Two p o i n t s have t o be checked c a r e f u l l y : t h e bond between t h e superconducting composite and t h e s t a b i l i z e d aluminium must have e x c e l l e n t mechanical and e l e c t r i c a l p r o p e r t i e s and t h e superconductor i t s e l f must p r e s e n t no d e f e c t , e i t h e r f r o m i t s o r i g i n a l p r o c e s s i n g o r f r o m damage d u r i n g t h e Aluminium c l a d d i n g o p e r a t i o n .

Two t e c h n i q u e s a r e b e i n g developed b y s e v e r a l European and Japanese m a n u f a c t u r e r s f o r t h e r e q u i r e d c o n d u c t o r : 1 - s o f t s o l d e r i n g o f a c a b l e (made o f Cu/NbTi s t r a n d s ) i n t o an aluminium channel ( t e c h n i q u e a l r e a d y used f o r t h e CELLO c o n d u c t o r ) . 2 - C o - e x t r u s i o n o f Aluminium around a Cu/NbTi composite e i t h e r m o n o l i t h i c o r cabled.

The o v e r a l l dimensions of t h e r e q u i r e d c o n d u c t o r a r e 3. 6 x 35 mm2.

The i n s e r t composize can be a m o n o l i t h r e c t a n g u l a r c o n d u c t o r 1. 8 x 3. 6 mm2 o r a 14 s t r a n d R u t h e r f o r d c a b l e 1 . 4 x 6 mm2 w i t h a r a t i o o f Cu/SC between 1 : 1 t o 2 : 1.

The r a t e d c u r r e n t i s 8 000 Amps a t 2 T and 4. 6 K. An RRR o f 500 t o 1 OUu i s r e q u i r e d f o r t h e A1 u-Sta'bi 1 iz e r .

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4

-

CONDUCTOR QUALIFICATION TESTS

A t e s t program has been i n i t i a t e d i n o r d e r t o measure t h e - r e l e v a n t c h a r a c t e - r i s t i c s o f t h e v a r i o u s c o n d u c t o r s under development and t o compare t h e i r p e r f o r - mances b e f o r e making t h e f i n a l choice. A t a l a t e r s t a g e q u a l i t y c o n t r o l w i l l be needed on t h e c o n t i n u o u s l e n g t h s d u r i n g p r o d u c t i o n .

P r e s e n t t e s t s a r e t h e f o l l o w i n g . 4. 1 Mechanical t e s t s

---

Usual t e s t s such as s t r e s s / s t r a i n c h a r a c t e r i s t i c s , Young's modulus and, most i m p o r t a n t , s h e a r i n g s t r e n g t h o f t h e bond between t h e Aluminium m a t r i x and t h e i n s e r t c o n d u c t o r a r e c a r r i e d o u t . Another way o f c h e c k i n g t h e bond i s b y m i c r o g r a p h y and X-ray a n a l y s i s .

Continuous q u a l i t y c o n t r o l w i l l concern s i z e t o l e r a n c e s and bond q u a l i t y ( u l t r a s o n i c method).

4. 2 E l e c t r i c a l t e s t s

---

R o u t i n e t e s t s c o n s i s t o f s h o r t sample measurements o f t h e B - I c h a r a c t e - r i s t i c s and o f t h e Aluminium r e s i s t i v i t y versus temperature and f i e l d .

More s p e c i f i c t e s t s have been developed f o r measuring t h e r e s i s t i v e p r o p e r - t i e s o f t h e bond between t h e Cu-composite and t h e Aluminium.

The o b j e c t i v e o f t h e 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 i s t o e s t a b l i s h a t e s t i n g procedure w h i c h w i l l p e r m i t a q u a n t i t a t i v e comparison o f d i f q e r e n t bonds by t h e measurement o f t h e e l e c t r i c a l c o n t a c t r e s i s t a n c e . The c u r r e n t t r a n s f e r f r o m a superconductor w i r e t o a normal m e t a l t a k e s p l a c e o v e r a c h a r a c t e r i s t i c l e n g t h , t h e s o - c a l l e d " t r a n s f e r l e n g t h " , which depends on t h e r e s i s t i v i t y o f t h e c o n t a c t b a r r i e r and on t h e r e s i s t i v i t y o f t h e s t a b i l i z e r :

Where rt i s t h e c o n t a c t s u r f a c e r e s i s t a n c e ( i n a m ) which a p p l i e s t o each u n i t l e n g t h o f conductor, and

PAr

/ AA1 i s t h e l i n e a r r e s i s t a n c e o f t h e s t a b i l i z e r .

I n o r d e r t o f o r c e a l l t h e c u r r e n t t o t r a n s f e r f r o m t h e superconductor t o t h e aluminium, t h e superconductor i s removed on a 4 cm - l e n g t h o f c o n d u c t o r . V o l t a g e t a p s a r e p l a c e d a l o n g t h e c o n t a c t area, t h e l e n g t h o f which i s 32 cm on b o t h s i d e s o f t h e p a r t w i t h o u t superconductor. The sample i s immersed i n l i q u i d h e l i u m and f e d w i t h l o w c u r r e n t s i n l o w f i e l d s so t h a t t h e superconductor remains i n i t s s u p e r c o n d u c t i n g s t a t e w i t h z e r o r e s i s t a n c e t h r o u g h o u t t h e l e n g t h o f c o n t a c t . Two c o n d u c t o r s w i t h d i f f e r e n t bond q u a l i t i e s have been t e s t e d . V o l t a g e measurements were taken a t each o f t h e t a p s w i t h one end o f t h e c o n d u c t o r s e r v i n g as t h e

r e f e r e n c e . F i g u r e 3 i s a p l o t o f v o l t a g e versus d i s t a n c e f o r t e s t c o n d u c t o r n O l i n z e r o magnetic f i e l d . I t i s assumed t h a t a n average u n i f o r m l y d i s t r i b u t e d

s u r f a c e r e s i s t a n c e e x i s t s between t h e superconductor and t h e aluminium and t h a t t h e t r a n v e r s e r e s i s t a n c e o f t h e a1 uminium i s n e g l i g i b l e compared t o t h e c o n t a c t r e s i s t a n - ce. The g l o b a l c o n t a c t r e s i s t a n c e i s g i v e n by t h e p o t e n t i a l d i f f e r e n c e a t t h e end o f t h e whole sample which i s equal t o :

Q A ~ ( L ⁺ I t ) AAl = G I I. L / A ~ , + ~A ~ ~ ~ ~ ~ ~ ' ~ ~

A 1

Table 2 g i v e s t h e values o f rt and It o b t a i n e d a t d i f f e r e n t magnetic f i e l d s f o r t h e two measured samples. C a l c u l a t e d v a l u e s shown in t a b l e 2 aregbased on t h e assumption of a 2 p i n t e r f a c e Alu-Cu w i t h a r e s i s t i v i t y o f 2.10- a m and compare r e a s o n a b l y w e l l w i t h t h e measured data. The r e s u l t s found w i t h c o n d u c t o r 2 show t h e e f f e c t o f a bad c o n t a c t between A1 and Cu, which was a l r e a d y observed on t h i s p a r t i c u l a r sample.

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JOURNAL DE PHYSIQUE

Table 2 V (pVJhA

40

20

0

4. 3 Propagating v e l o c i t y of t h e normal zone 8 , O r

1,1056 A

..

-

U /, ^I +

...

Quench t e s t s a r e performed t o measure propagation v e l o c i t i e s , both longitudinal and t r a n s v e r s e . For t r a n s v e r s e v e l o c i t y , a pancake-type c o i l i s used.

The pancake has a 40 mm ID and 180 mm OD and c o n t a i n s 16 t u r n s . I t i s thermally i n s u l a t e d from t h e helium bath by t h i c k l a y e r s of f i b e r glass.and epoxy. An e l e c t r i c a l h e a t e r i s inbedded i n s i d e the c o i l and covers a whole t u r n , so a s t o induce r a d i a l ( t r a n s v e r s e ) propagation. The v e l o c i t y of propagation i s c a l c u l a t e d from t h e terminal voltage evolution of t h e c o i l and from t h e times when r e s i s t i v e voltages appear a t d i s t r i b u t e d voltage t a p s along t h e conductor.

Results a r e shown in Fig 4 f o r conductorl(same a s i n t a b l e 2) wound with a 0. 4 mm i n s u l a t i o n between t u r n s (epoxy glued).

Calculated values of t h i s v e l o c i t y a r e a l s o shown on Fig 4, using c l a s s i c a l formulae, which do not take i n t o account t h e c u r r e n t d i f f u s i o n time in t h e l a r g e width of t h e pure A l u - s t a b i l i z e r . The l a r g e d e v i a t i o n between experimental and c a l c u l a t e d values may be explained by this l a s t e f f e c t and a l s o by t h e presence

0 15 1 k 1* 19

&

²⁷ ³⁶ ^{x h m )}

]en th w;thout - '

sISpcPconductoP

Fig 3 - P o t e n t i a l d i s t r i b u t i o n f o r conductor f

RRR

428

1080 rt@m)

ExP

0.7 10-I' 1 . 3 10-lo 2.510-'O 1 . 8 10-lo

8 1 0 ~ ~ ~

16.5 10-lo

CROSS SECTION mm ²

3,6x20

3,6x35

-

v-l

+

-0 %

0

+-' 0

u

3 -0 c

0 U

1 t(mm) E x P

0.8 6.5 7 . 5 27 28 3 5 r t ( f i m )

CALCULATED

3.3 lo-'' 3.3 10-l1 6.610-'I

qT)

0 3 6

0

3 6

lt(mrn) CALCULATED

2.2 4.4 6.1

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CONDUCTDR 1

I

Fig 4 - Transverse quench propagation v e l o c i t y

of a longitudinal component of the v e l o c i t y which cannot be completely eliminated.

A d i r e c t measurement of t h e longitudinal v e l o c i t y i s being prepared, using a helix- type t e s t c o i l . The same measurements w i l l then be extended t o t h e f u l l s i z e conductor.

5 - CONCLUSION

The method developed f o r c o n t a c t r e s i s t a n c e measurement appears appro- p r i a t e f o r t h e estimation of bond q u a l i t y and w i l l be used f o r q u a l i f y i n g t h e various conductors under development.

On t h e o t h e r hand, measured v e l o c i t i e s of propagation of t h e normal zone a r e found s u b s t a n t i a l l y higher than those predicted by usual theory and which were used f o r preliminary a n a l y s i s of t h e quench evolution of t h e ALEPH c o i l . This e f f e c t i s most favorable with regard t o t h e s a f e t y of t h e c o i l .