DESIGN STUDY OF A THIN, SUPERCONDUCTING SOLENOID

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DESIGN STUDY OF A THIN, SUPERCONDUCTING SOLENOID

J. Zellweger, G. Vécsey, H.-Ch. Walter, J. Crawford, P. Reeve

To cite this version:

J. Zellweger, G. Vécsey, H.-Ch. Walter, J. Crawford, P. Reeve. DESIGN STUDY OF A THIN,

SUPERCONDUCTING SOLENOID. Journal de Physique Colloques, 1984, 45 (C1), pp.C1-351-C1-

356. �10.1051/jphyscol:1984172�. �jpa-00223728�

DESIGN STUDY OF A THIN, SUPERCONDUCTING SOLENOID

J . Z e l l w e g e r , G. V e c s e y , H.-Ch. W a l t e r , J . Crawford and P.A. Reeve*

Suiss Institute for Nuclear Research, CH-5234 Villigen, Switzerland

*TRTUMF, University of B.C., Vancouver VST 2A3, Canada

Résumé - Une étude de construction d'un spectromètre cylindrique avec un diamètre de 1,3 m et une longueur de 1,3 m est présentée. Le champ magnéti- que de 1,7 T est produit par une bobine supraconductrice. Une homogénéité de il% est demandée. L'épaisseur totale de la bobine, chambre à vide inclue, est limitée à 0,6 de la longueur de radiation des photons. On a étudié deux solu- tions : d'abord une bobine composée d'un supraconducteur de Nb-Ti stabilisé avec aluminium ensuite un solenoïde transformateur avec un bobinage primaire supraconducteur et un secondaire normal en aluminium. Dans les deux cas la bo- bine est refroidie indirectement par écoulement forcé d'hélium supercritique à une pression de 10 bar et une température de 4,5 K, une technologie qui est bien établie en SIN.

A b s t r a c t - A d e s i g n s t u d y f o r a t h i n 1 .7 T s u p e r c o n d u c t i n g s o l e n o i d s p e c t r o m e t e r of 1 .3 m d i a m e t e r and 1.3 m l e n g t h i s p r e s e n t e d . A f i e l d homogeneity of ± 1 $ i s r e q u i r e d . The o v e r a l l m a t e r i a l t h i c k n e s s of c o i l and vacuum chamber i s l i m i t e d t o 0.6 photon r a d i a t i o n l e n g t h . Two v e r s i o n s were s t u d i e d : A s i n g l e l a y e r c o i l wound w i t h A l - s t a b i l l z e d N b - T i - s u p e r c o n d u c t o r and t r a n s f o r m e r s o l e n o i d w i t h a s u p e r c o n d u c t i n g p r i m a r y w i n d i n g a a normal c o n d u c t i n g s e c o n d a r y w i n d i n g made o u t of A l . I n both c a s e s t h e c o i l i s c o o l e d i n d i r e c t l y by f o r c e d flow of s u p e r c r i t i c a l He a t 1 0 b a r and 4 . 5 K - a t e c h n o l o g y d e v e l o p e d a t SIN.

I - INTRODUCTION

For t h e s t u d y of f l a v o u r c h a n g i n g muon d e c a y s and o t h e r r a r e muon and p i o n r e a c t i o n s a l a r g e , s u p e r c o n d u c t i n g photon t r a n s p a r e n t m a g n e t i c s o l e n o i d s p e c t r o m e t e r of h i g h f i e l d i s needed. D e t a i l e d i n f o r m a t i o n of t h e e x p e r i m e n t s and of t h e s p e c t r o m e t e r a s s e m b l y i s g i v e n i n Ref. / 1 / . Magnet d e s i g n a s p e c t s a r e '. r e p o r t e d i n C h a p t e r 2 .

The b a s i c d e s i g n d a t a f o r t h e SIN s o l e n o i d i s l i s t e d :

a ) A homogeneous m a g n e t i c f i e l d of up t o 1 .7T \% must be r e a c h e d i n a c y l i n d r i c a l volume of 1 .2m d i a m e t e r and 1m l e n g t h .

b ) The c o i l assembly c o n s i s t i n g of vacuum chamber, t h e r m a l s h i e l d s and s u p e r c o n d u c t i n g c o i l must be t r a n s p a r e n t f o r p h o t o n s . The m a t e r i a l t h i c k n e s s must not exceed 0.6 r a d i a t i o n l e n g t h .

c ) The geometry i s f i x e d by

C o i l d i m e n s i o n s : d i a m e t e r : 1.3 m; l e n g t h : 1.3 m C r y o s t a t l e n g t h : 1 .3 m

A c r o s s s e c t i o n a l view of c o i l and c r y o s t a t i n c l u d i n g i r o n y o k e and p o l e p l a t e s i s g i v e n i n F i g . 1 a, b . The shape of t h e i r o n p a r t s a r e mainly d e f i n e d by p r i m a r y beam, v a r i o u s s e n s o r s a c c e s s t o measurements and s o on.

S i m i l a r t h i n , t r a n s p a r e n t s u p e r c o n d u c t i n g s o l e n o i d s have been b u i l t i n F r a n c e : C e l l o / 3 / , i n USA: PEP / 4 / , i n Geneva: ISR / 5 / .

Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:1984172

JOURNAL DE PHYSIQUE

F i g u r e 1 a:

C r o s s s e c t i o n a l view of s o l e n o i d , c r y o s t a t and I r o n y o k e s and m i r r o r p l a t e s .

F i g u r e Ib:

C r o s s s e c t i o n a l view of s o l e n o i d c r y o s t a t and i r o n .

I1 - MAGNET PARAMETERS AT STATIONARY CONDITION

F o r t h e g i v e n c o i l d i m e n s i o n s and t h e d e s i r e d B - f i e l d t h e f o l l o w i n g d a t a summarized i n T a b l e

- were c a l c u l a t e d b a s e d upon t h e model o f p e r f e c t m i r r o r s .

TABLE 1 - Main Parameters o f t h e C o i l

R e f i n e d computer c a l - c u l a t i o n s l i m i t e d t h e d e c e n t e r i n g f o r c e t o 12 to/cm.

I n a d d i t i o n I n a d d i t i o n t h e i n - homogeneity due t o t h e non i d e a l l y s h a p e d i r o n p a r t s was s t u d i e d more c a r e f u l l y . D e t a i l s a r e r e p o r t e d i n Ref 6 .

~ o m e n t

Main p a r a m e t e r s : B - f i e l d on conductor Magnetic energy Amp. t u r n s

F o r c e s : a t t r a c t i n g f o r c e : c o i l - i r o n d e c e n t e r i n g f o r c e i n a x i a l d i r e c t i o n p e r lcm a x i a l d i s p l a c e m e n t c e n t e r i n g t o r q u e due t o a 1°C r o t a t i o n r e l a t i v e t o t h e main a x i s P r e s s u r e : Magnetic p r e s s u r e on winding

Data

B = 1 . 7 T E = 2.0 M J N I = 1.76 Mega-A F < 150 t o dF/dz < 22.5 t o

d ~ / d ( W I ) = 3 . 4 t o 1°c

p = 11.5 kp/cm

A) G e n e r a l F e a t u r e s :

B a s i c a l l y two conduct o r c o n c e p t s were s t u d i e d , which f u l f i l l t h e t r a n s p a r e n c y r e q u i r e m e n t . F u r t h e r o n , we assume t h a t t h e r a d i a l f o r c e i s t a k e n by t h e c o o l i n g t u b e . T h e r e f o r e , no a d d i t i o n a l r e i n f o r c e m e n t m a t e r i a l i n t h e c o n d u c t o r i s n e c e s s a r y .

V e r s i o n 1

A m o n o l i t h i c Nb-Ti f i l a m e n t c o n d u c t o r w i t h c o p p e r m a t r i x i n m e t a l l i c c o n t a c t w i t h h i g h p u r i t y aluminium c o n d u c t o r s i m i l a r t o t h e CELLO d e s i g n was s t u d i e d . The b e s t s o l u t i o n

a Nb-Ti c o n d u c t o r c o e x t r u d e d w i t h aluminium. ( s e e : F i g . 2 a )

V e r s i o n 2: The c o i l w l n d i n g c o n s i s t s of a s u p e r c o n d u c t i n g Nb-Ti p r i m a r y w i n d i n g and a normal c o n d u c t i n g , h i g h p u r i t y aluminium s e c o n d a r y winding. The l a t t e r a c t s a s a t r a n s f o r m e r w i n d i n g a n d i s u s e d f o r t h e e n e r g y dump f o l l o w i n g a quench. Conductor o f b o t h w i n d i n g s a r e shown i n F i g . 2b.

A s i m i l a r d e s i g n i s u s e d i n t h e TPC-coil (USA). C o n t r a r y t o t h e i r d e s i g n t h e s e c o n d a r y w i n d i n g i s n o t s h o r t e d b u t c o n n e c t e d t o a n e x t e r n a l r e s i s t o r o u t s i d e t h e vacuum chamber. The d i s c h a r g e t i m e i s k e p t r e a s o n a b l y low t o be a b l e t o u s e commercial power s w i t c h e s i n s t e a d o f SCR's a s i n t h e TPC-version.

F i g u r e 2a:

7 i

V e r s i o n A c o n d u c t o r

F i g u r e 2b:

V e r s i o n B c o n d u c t o r

B ) Conductor and i t s o p e r a t i n g p a r a m e t e r s :

The o p e r a t i n g c u r r e n t of t h e 1 .7T s o l e n o i d was chosen t o be 2500A a t a maximum t e m p e r a t u r e of 5.5K. The c r i t i c a l c u r r e n t s h o u l d be above 2750A a t t h i s t e m p e r a t u r e . The f i l a k n t d i a m e t e r i s f i x e d t o a p p r . 30pm a n d t h e t w i s t p i t c h

9 ^{. .}

is lcm. F o r quench c o n d l t l o n s t h e d i s c h a r g e t i m e was s e t t o 2 s e c f o r v e r s i o n A ) and 0.2 s e c f o r v e r s i o n B ) ( s u p e r c o n d u c t o r ) . The h o t s p o t t e m p e r a t u r e s h o u l d n o t exceed 100K. R e l e v a n t d i s c h a r g e c i r c u i t s a r e shown i n F i g . 3 a , b. Quench boundary c o n d i t i o n s f o r t h e c o n d u c t o r a r e l i s t e d i n T a b l e 2 , whereas i m p o r t a n t c o n d u c t o r p a r a m e t e r s a r e l i s t e d i n T a b l e 3.

TABLE 2 - Quench Boundary Conditions f o r Conductor Design

diode cascade ,

---

(forward voltage') ' inductance ( L ) 0.64 H Comment

mutual inductance ( M ) Resistance ( R )

1

VERSION A

I

I

power-switch -50 msec

I

VERSION B

<50 msec -50 msec

I

0.64 H -0.63 H

0.32 Ohm

I ^I

200 msec

1

1

JOURNAL DE PHYSIQUE

TABLE 3 - Important Conductor Parameters

nominal current max.amb-ant temperature rnagn. field

critical current (2T, 5.5K)

overall current density of conductor current density of stabilizing material RRR-Cu

RRR-Alu

A1-Cu (Nb-Ti) ratio conductor area max. conductor temp.

hot spot temperature

Version A

2500 A 5.5 K 1.7 T 2750 A

146 ~ / m '

160 P./mm2

100 250 18-1.3-1.0 17.5 mm2

~ 7 5 K 100 K

Version B

p r i m a r y conductor

I

( 1.7T) 2750 A

F i g u r e 3:

S c h e m a t i c d i a g r a m o f t h e

" 0 2

d i s c h a r g e c i r c u i t

R o t a t i o n : R = R e s i s t o r , L= I n d u c t a n c e

M=Mutual I n d u c t a n c e , S=Power S w i t c h , U ~ D i o d e f o r w a r d V o l t a g e ,

3a 3b ( u D 1 =800V, uD2 1ov)

I V - COIL DESIGN A ) D e s c r i p t i o n :

A 4mm t h i c k aluminium t u b e of 1 .3m d i a m e t e r w i t h two end r i n g s welded on e a c h s i d e s u p p o r t s t h e i n s u l a t e d p r i m a r y o r s e c o n d a r y wind'ing a s s e e n i n F i g . 4 . The i n s u l a t e d c o o l i n g t u b e - a t o t a l o f t e n c o o l i n g c i r c u i t s - i s wound on t o p o f t h e winding. The aluminium f o r m e r , t h e c o o l i n g t u b e s and t h e c o n d u c t o r l a y e r s a r e vacuum i m p r e g n a t e d t o improve t h e i n s u l a t i o n a n d g u a r a n t e e h e a t exchange d u e t o l o c a l t e m p e r a t u r e g r a d i e n t s . The q u a d r a t i c c o o l i n g t u b e must w i t h s t a n d 1 5 0 b a r i n c a s e o f a quench. I t s dimensions a r e 12x12 mm and i t s i n n e r d i a m e t e r is 1 0 mm. The s o l e n o i d i s p o s i t i o n e d and a l i g n e d a z i m u t h a l l y , r a d i a l l y and l o n g i t u d i n a l l y r e l a t i v e t o t h e vacuum-chamber and "I r o n - M i r r o r s " by a p p r o p r i a t e r o d s , which a c t on t h e end r i n g s .

B ) C o o l i n g c o n c e p t :

A c c o r d i n g t o t h e c o o l i n g c o n c e p t u s e d i n t h e muon c h a n n e l s /7/ a n d s e e n i n

Fig. 5 t h e s o l e n o i d and i t s s u s p e n s i o n r e p r e s e n t s e p a r a t e t h e r m a l l o a d s , which

a r e s u b d i v i d e d i n t o 10 s o l e n o i d and two s u s p e n s i o n c o o l i n g c i r c u i t s .

S u p e r c r i t i c a l h e l i u m a t 4.5K and 10 b a r l e a v i n g a h e l i u m b a t h h e a t e x c h a n g e r i s

c i r c u l a t e d between c o o l i n g c i r c u i t s and b a t h h e a t e x c h a n g e r s . F i n a l l y , t h e

s u p e r c r i t i c a l h e l i u m h a v i n g p a s s e d a l l c o o l i n g c i r c u i t i s expanded i n t o t h e

h e l i u m b a t h by a J o u l e Thompson v a l v e . I n t h e c o l d s t a t e a l l c i r c u i t s a r e

c o n n e c t e d i n s e r i e s . Massflow c o n t r o l i s done w i t h t h e J o u l e Thompson v a l v e by

k e e p i n g t h e h e l i u m b a t h l e v e l c o n s t a n t . The b a t h t e m p e r a t u r e i s a l s o k e p t

c o n s t a n t by b a t h p r e s s u r e c o n t r o l . The e x p e c t e d t h e r m a l l o a d i s 65W. The

c u r r e n t l e a d s , which a r e h e l i u m v a p o r c o o l e d , a r e a n a d d i t i o n a l l o a d .

A c c o u n t i n g 0.5 gm/sec f o r t h e l e a d s , t h e t o t a l He-massflow is 4.8 gm/sec. The

t h e r m a l h e a t s h i e l d s , a t a b o u t 90K, a r e a l s o h e l i u m c o o l e d . The e x p e c t e d h e a t

l o a d i s 1000W.

C r o s s s e c t i o n t h r o u g h t h e c r y o s t a t and t h e c o i l ( v e r s i o n B ) :

( 1 ) I n n e r c r y o s t a t w a l l ,

( 2 ) Vacuum w i t h s u p e r i n s u l a t i o n (3) N i t r o g e n s h i e l d ,

( 4 ) O u t e r honeycomb c r y o s t a t w a l l , ( 5 ) C o i l s u p p o r t c y l i n d e r ,

( 6 ) G l a s s mesh i n s u l a t i o n ( 7 ) Pure A1 s e c o n d a r y w i n d i n g , (8) Cu-Nb-Ti s u p e r c o n d u c t o r

w i n d i n g ( 9 ) C o o l i n g t u b e s

F i g u r e 5:

S c h e m a t i c d i a g r a m o f c o o l i n g c i r c u i t g o t a t i o n

-vvv- hes.t e x c h a n g e r

0 0

S u s ? e n s i o S u s p e n s i o n

V - ^CRYOSTAT

Thermal r a d i a t i o n s h i e l d s made o u t o f aluminium a t a p p r o x i m a t e l y 90K s u r r o u n d e d t h e

c o i l s u r f a c e . They a r e mounted i n t h e c r y o s t a t . ( s e e : ~ i ~ . 4 ) . C o i l a n d t h e r m a l

s h i e l d s c a r r y s e v e r a l l a y e r s o f s u p e r i n s u l a t i o n , which i s a common method f o r

r e d u c i n g t h e r m a l r a d i a t i o n l o s s e s . The c r y o s t a t must be l e a k t i g h t and must

s u f f i c e t h e f o r c e r e q u i r e m e n t s w i t h r e g a r d t o m e c h a n i c a l s t a b i l i t y . F o r c e s a r i s e

from vacuum p r e s s u r e a n d from 0 . 5 b a r peak r a d i a l p r e s s u r e d u e t o eddy c u r r e n t s

d u r i n g quench d i s c h a r g e . F o r t h e o u t e r c r y o s t a t w a l l , which must be d e s i g n e d t o

a v o i d b u c k l i n g , a honeycomb r e i n f o r c e d s t r u c t u r e o f low t r a n s p a r e n c y i s s u g g e s t e d ,

o t h e r w i s e a n aluminium s h e l l o f a t l e a s t 1 2 mm t h i c k n e s s i s r e q u i r e d . I n a l l c a s e s

t h e t r a n s p a r e n c y r e q u i r e m e n t i s f u l f i l l e d a n d t h e magnet m a t e r i a l t h i c k n e s s does

n o t exceed 0.57 r a d i a t i o n l e n g t h .

JOURNAL DE PHYSIQUE

REFERENCES

/1/ E n g f e r R . , Domingo J . , W a l t e r H . C . , e t a l . , SINDRUM-Proposal, SIN.

/2/ Z e l l w e g e r J . , I n t e r n a l R e p o r t KRYO-81.11 , SIN (1981).

/3/ Genevey P . , l e B a r s J . , 6 t h I n t e r n a t i o n a l C o n f e r e n c e on Magnet Technology (MT-61, B r a t i s l a v a , (1977).

/4/ Green M.A. e t a l . , Adv. C r y o g . E n g . 3 , (1980).

/5/ Morpurgo M . , C r y o g e n i c s , F e b r u a r y (1977) 89.

/6/ Reeve P.A., I n t e r n a l R e p o r t , KRYO-81 . l o , SIN (1981).

/7/ Vecsey G . , 5 t h I n t e r n a t i o n a l C o n f e r e n c e on Magnet Technology (MT-5), Roma

f ^1975).