SUPERCONDUCTING COIL INSTRUMENTATION

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Submitted on 1 Jan 1984

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SUPERCONDUCTING COIL INSTRUMENTATION

G. Vécsey

To cite this version:

G. Vécsey. SUPERCONDUCTING COIL INSTRUMENTATION. Journal de Physique Colloques, 1984, 45 (C1), pp.C1-643-C1-648. �10.1051/jphyscol:19841130�. �jpa-00223601�

JOURNAL DE PHYSIQUE

Colloque C1, suppl6ment au n o 1, Tome 45, janvier 1984 page C1-643

SUPERCONDUCTING COIL INSTRUMENTATION

G . VQcsey

Swiss Institute for Nuclear Research (SIN), 5234 Villigen, SwitzerZand

Rhsum6 - C e t a r t i c l e p r Q s e n t e une r e v u e d e s c a p t e u r s l e s p l u s u s u e l s p o u r l a s u r v e i l l a n c e d ' a i m a n t s s u p r a c o n d u c t e u r s , s u i v i e d e q u e l q u e s exemples d e g r a n d s s y s t l m e s d ' i n s t r u m e n t a t i o n e t d e l e u r f o n c t i o n n e m e n t . C e r t a i n s r i s q u e s l i 6 s P d e s systBmes d ' i n s t r u m e n t a t i o n compliqu6s a i n s i que l e u r s d5veloppements f u t u r s s o n t a n a l y s g s P p a r t i r d e l ' e x p b r i e n c e p r a t i q u e a c q u i s e a v e c d e g r a n d s aimant s

.

A b s t r a c t - A s u r v e y of c h a r a c t e r i s t i c s e n s o r s f r e q u e n t l y a p p l i e d i n s u p e r c o n d u c t i n g magnet m o n i t o r i n g is f o l l o w e d by a few examples of l a r g e i n s t r u m e n t a t i o n s y s t e m s and a review on t h e i r o p e r a t i o n a l e x p e r i e n c e . An a t t e m p t is made t o i n d i c a t e some of t h e r i s k s r e l a t e d t o s o p h i s t i c a t e d i n s t r u m e n t a t i o n s y s t e m s and t o a n a l y s e f u t u r e t r e n d s on t h e b a s i s of r o u t i n e o p e r a t i o n e x p e r i e n c e i n l a r g e magnet s y s t e m .

1

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We s k i p t h e f i r s t 50 h e r o i c y e a r s of t h e h i s t o r y of s u p e r c o n d u c t i v i t y a s i t is more a p p r o p r i a t e t o remember, t h a t t h e f i r s t l a b o r a t o r y s u p e r c o n d u c t i n g c o i l produced 10 T e s l a j u s t 20 y e a r s ago i n 1967. The i n s t r u m e n t a t i o n f o r t h e 7 cm OD NbSn d e l r ~ o n s t r a t i o n c o i l c o n s i s t e d o f a diaphragm l e v e l s e n s o r , two m e t e r s f o r v o l t a g e and c u r r e n t and a compass. S i n c e t h e n enormeous p r o g r e s s was made i n s u p e r c o n d u c t i n g t e c h n o l o g y and c r y o g e n i c s .

S t a r t i n g w i t h u n s t a b l e s i n g l e c o r e NbZr w i r e s of more o r l e s s u n p r e d i c t a b l e performance i n t h e s e two decades we l e a r n e d t o u n d e r s t a n d , f a b r i c a t e , h a n d l e and t o r e l y upon f u l l y t r a n s p o s e d , m u l t i s t a g e , composite, h i g h c u r r e n t , h i g h f i e l d c o n d u c t o r s w i t h hundred t h o u s a n d s of f i l a m e n t s ; p o s s i b l y t h e y a r e f o r c e - f low c o o l e d o r e v e n h e a v i l y i r r a d i a t e d and, o f t e n enough, s t i l l w o r k i n g r e l i a b l y u n d e r s o c a l l e d " u n s t a b l e " c o n d i t i o n s .

I n c r e a s i n g l y sound e n g i n e e r i n g and c o n d u c t o r development f o r l a r g e s u p e r c o n d u c t i n g magnets a p p l i e d i n h i g h e n e r g y p h y s i c s p a w d t h e way f o r t h e i n d u s t r i a l d e w l o p m e n t

and d e m o n s t r a t i o n of most p o t e n t i a l a p p l i c a t i o n s e v e r proposed.

H o p e f u l l y soon, s u p e r c o n d u c t i n g c o i l s w i l l become rugged and r e l i a b l e b a s i c components of f a c i l i t i e s f o r t h e g e n e r a t i o n , c o n v e r s i o n and s t o r a g e of e n e r g y , of l e v i t a t e d t r a n s p o r t s y s t e m s , i n d u s t r i a l p r o c e s s i n g equipment and of d e v i c e s f o r m e d i c a l d i a g n o s t i c s and t r e a t m e n t .

Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:19841130

C1-644 JOURNAL DE PHYSIQUE

A t p r e s e n t , i n t h e development and d e m o n s t r a t i o n p h a s e o f a new t e c h n o l o g y , t h e demand f o r i n s t r u m e n t a t i o n i s a t i t s h i g h e s t l e v e l . Normally i t s h o u l d d r o p t o a minimum, once t h e p r o v e n t e c h n o l o g y is a c c e p t e d . The f i n a l need w i l l be d e f i n e d by a b a l a n c e of t h e c o n c u r r e n t t r e n d s t o less based on h i g h c o n f i d e n c e and t o more i f t h e a p p l i c a t i o n s y s t e m h a s h i g h l y complex dynamics ( c o n t r o l and d i a g n o s t i c s ) . The l a t t e r is s u r e l y t h e c a s e a t l e a s t f o r f u s i o n r e a c t o r a p p l i c a t i o n s . The q u e s t i o n seems t h e r e f o r e t o be j u s t i f i e d : Did t h e development i n i n s t r u m e n t a t i o n cope w i t h t h e demand o f c o i l s y s t e m p e r f e c t i o n ?

2 . SENSORS

Concerning s e n s o r s t h e answer t o t h e above q u e s t i o n s h o u l d be " n o t r e a l l y " . I n f a c t , most b a s i c c r y o g e n i c s e n s i n g e l e m e n t s were a v a i l a b l e twenty y e a r s ago. I t is h a r d t o i d e n t i f y a r e a l s i g n i f i c a n t s t e p i n any of t h e f i e l d s s h o r t l y reviewed be low.

2 .I Temperature:

For t h o s e w i t h more academic i n t e r e s t ( o r t h o s e j u s t g i v i n g up t h e home c a l i b r a t i o n of s e c o n d a r y s e n s o r s b a s e d on v a p o r - p r e s s u r e - r e f e r e n c e ) i s good t o know, t h a t s t i l l r e c e n t l y p r o g r e s s h a s been made ( E P T ~ ~ ) i n t h e d e f i n i t i o n o f t h e t e m p e r a t u r e s c a l e 121.

F o r more p r a c t i c a l l y o r i e n t e d c o i l d e s i g n e r s F i g u r e 1 / 2 / g i v e s a comprehensive s u r v e y of t h e c h a r a c t e r i s t i c s of p a s s i v e l e c t r o n i c l o w - t e m p e r a t u r e s e n s o r s . The f u l l r a n g e s e n s i t i v i t y and r e l a t i v e l y good l i n e a r i t y of d i o d e s (GaAs, S i ) , a p p r e c i a t e d e a r l i e r , and t h e h i g h p r e c i s i o n o f Ge thermometers ( 0.5 mK a t 4.2 K) is i n most p r a c t i c a l c a s e s of l i m i t e d i m p o r t a n c e . Both t y p e s a r e extiremely s e n s i t i v e t o h i g h m a g n e t i c f i e l d s , w i t h o r i e n t a t i o n - d e p e n d e n t e r r o r s o f t h e o r d e r of 30% a t 4.2 K and 8 T /3/.

Fig.1 - S e n s i t i v i t y of p a s s i v e t e m p e r a t u r e s e n s o r s S i , GaAs D i o d e s , Germanium R e s i s t a n c e Thermometer, Carbon G l a s s R e s i s t a n c e Thermometers, P l a t i n u m R e s i s t o r s /6/.

F i g . 2 - Magnetic F i e l d I n f l u e n c e on P l a t i n u m a n d Carbon-Glass R e s i s t a n c e Thermometers 141.

The p r o p e r c h o i c e i n most magnet s y s t e m a p p l i c a t i o n s is t h e c a r b o n - g l a s s thermometer (CGRT) w i t h e x t r e m e l y low s y s t e m a t i c ( i . e . c o r r e c t a b l e ) and d i r e c t i o n i n d e p e n t f i e l d s e n s i t i v i t y , a s i l l u s t r a t e d i n F i g u r e 2 /4/. F o r t h e i n t e r m e d i a t e t e m p e r a t u r e r a n g e (cooldown, p r o c e s s c i r c u i t ) i t can be u s e d w i t h s u f f i c i e n t p r e c i s i o n a t h i g h e r c u r r e n t s , o r can be complemented by t h e r m o c o u p l e s o r P t r e s i s t a n c e s e n s o r s

.

Time c o n s t a n t s a r e i n g e n e r a l s u f f i c i e n t l y low f o r p r a c t i c a l a p p l i c a t i o n s . The need f o r i n d i v i d u a l c a l i b r a t i o n , commercially a v a i l a b l e , and f o r 4 w i r e c o n n e c t i o n remain drawbacks we have t o g e t u s e d t o .

2.2 P r e s s u r e :

P r e s s u r e - and d i f f e r e n t i a l p r e s s u r e - t a p s a r e n o r m a l l y c o n n e c t e d t o c o n v e n t i o n a l room t e m p e r a t u r e g a u g e s o r t r a n s d u c e r s . Long c a p i l l a r y c o n n e c t i o n s , p r e f e r r a b l y of SS w i t h welded c o n n e c t i o n s and f e e d t h r o u g l i s , a r e e v i d e n t l y i n c r e a s i g t i m e c o n s t a n t s and t h e r i s k of l e a k a g e . L e s s e v i d e n t , b u t of c a t a s t r o p h i c consequence can be f o r i n s t a n c e t h e r i s k of l e a k i n g dumping - f l u i d from a d e f e c t t r a n s d u c e r i n t o a r e f r i g e r a t i o n c i r c u i t .

Cold p r e s s u r e t r a n s d u c e r s were known t o be u n r e l i a b l e mainly b e c a u s e of t h e i r s e n s i t i v i t y t o t h e r m a l c y c l i n g , ho~fiever, s u c c e s s f u l a p p l i c a t i o n s a r e a l s o r e p o r t e d on s o l i d s t a t e t r a n s d u c e r s /5/. They w i l l have a c e r t a i n r e l e v a n c e , where t i m e l a g s a r e d i s t u r b i n g , i f t h e i r s e n s i t i v i t y t o h i g h f i e l d s c a n be t o l e r a t e d , o r c l i r n i n a t e d .

2.3 Kassf low:

S i n c e t h e f i r s t s u c c e s s f u l a p p l i c a t i o n s o f f o r c e d - f low c o o l i n g massf low measurements became i n c r e a s i n g l y r e l e v a n t f o r h e l i u m c i r c u i t s . O r i f i c e t y p e d e v i c e s proved t o be c o n v e n i e n t f o r many a p p l i c a t i o n s w i t h one p h a s e c o o l a n t /6/, even i f t h e y a r e non s t a n d a r d s i z e b u t d e s i g n e d a c c o r d i n g t o s t a n d a r d recommendation / 7 / . No d i r e c t s o l u t i o n is known f o r t h e measurement o f two-phase flow. G e n e r a l drawback of t h e t h r o t t l e d e v i c e s is t h e i r l i m i t e d i n d i v i d u a l r a n g e and t h e need f o r s i m u l t a n e o u s l o c a l p,T s e n s i n g .

2.4 L i q u i d Helium-Level:

I n t h e few c a s e s where t h e wide s p r e a d a p p l i c a t i o n o f commercial s u p e r c o n d u c t i n g w i r e s e n s o r s is p r e v e n t e d by t h e p r e s e n c e of h i g h m a g n e t i c f i e l d s t h e t e c h n i q u e of s l i g h t l y o v e r h e a t e d c a r b o n r e s i s t o r s can be u s e d .

2.5 S t r a i n :

D e s p i t e i t s i n c r e a s i n g r e l e v a n c e i n t e s t i n g o f l a r g e h i g h f i e l d s c magnets t h e problem o f s t r a i n c e a s u r e m e n t a t low t e m p e r a t u r e s seems n o t t o be s a t i s f a c t o r i l y r e s o l v e d . Although r e p r o d u c i b l e c o r r e c t i o n s f o r t h e t e m p e r a t u r e dependence o f t h e gauge f a c t o r and t h e f i e l d i n d u c e d e r r o r i n a p p a r e n t s t r a i n c a n be d e r i v e d f o r t h e i n d i v i d u a l s e n s o r s ( ~ r ~ ? i ) , t h e sample t o sample v a r i a t i o n o f t h e combined c o r r e c t i o n seems t o be d o u b t f u l even f o r c a r e f u l l y s e l e c t e d s e n s o r s o f t h e s a x e f a b r i c a t i o n l o t . C o n t r a d i c t o r y r e s u l t s o f ' q u a l i f i e d e x p e r t s i n d i c a t e a need f o r f u r t h e r c l a r i f i c a t i o n i n t h a t f i e l d / 8 / , /3/.

2.6 P,lagnetic I n d u c t i o n :

Commercially a v a i l a b l e low t e m p e r a t u r e h a l l - p r o b e s o f < ^I%o p r e c i s i o n a r e commonly u s e d h i g h l y r e l i a b l e i t e m s i f p r o p e r l y i n s t a l l e d . F o r h i g h e r p r e c i s i o n s t a n d a r d X'bR t e c h n i q u e s c a n be u s e d .

JOURNAL DE _PHYSIQUE

2.7 O t h e r s :

For l e s s f r e q u e n t s p e c i f i c a p p l i c a t i o n s c r a c k d e t e c t o r s , d i s p l a c e m e n t s e n s o r s , a c o u s t i c d e t e c t o r s e t c . have been d e v e l o p e d , f o r which t h e r e a d e r s h o u l d r e f e r t o t h e l i t e r a t u r e .

3 . DATA ACQUISITIOX AND CONTROL

The f i r s t i n t e g r a t e d c i r c u i t was d e v e l o p e d a b o u t t h e same t i m e a s 1 0 T were a c h i e v e d , and A D C - s a r e o n l y few y e a r s o l d e r . T h e i r tremendeous impact t o g e t h e r w i t h t h a t o f PLC-s (1970) and m i c r o p r o c e s s o r s (1974) overcornpensate f o r many of t h e f o r n ~ e r s e n s o r d e f i c i e n c i e s ( r a n g e l i m i t a t i o n s , nou l i n e a r i t y , i n d i v i d u a l c a l i b r a t i o n , e t c . ) Ever i n c r e a s i n g a c c u r a c y , r e p r o d u c i b i l i t y , s p e e d and f l e x i b i l i t y combined w i t h a u t o m a t e d s e q u e n c e o p t i o n s , r e l i a b l e s i g n a l c o n d i t i o n i n g e t c . up t o a u t o m a t i c c a l i b r a t i o n , L u i l t i n s e l f - c h e q u e and s e l f - d i a g n o s t i c f e a t u r e s become s t a n d a r d c h a r a c t e r i s t i c s of i n s t r u m e n t a t i o n even a t s m a l l s c a l l l a b o r a t o r y a p p l i c a t i o n s . T h e i r s t i l l o n g o i n g r a p i d development make any e f f o r t f o r a comprehensive review o b s o l e t e b e f o r e w r i t t e n down and would be a welcome s u b j e c t f o r a s e p a r a t e c o n f e r e n c e .

Some o f t h e advanced s y s t e m s i n t h e f i e l d s h o u l d be mentioned merely a s examples.

The PIOTRON /13/ i s a s u p e r c o n d u c t i n g p i o n i r r a d i a t i o n f a c i l i t y r o u t i n e l y o p e r a t e d by a m e d i c a l team a t SIN s i n c e 1980. I t s two t o r o i d a l magnets of 7 t o n s each w i t h a t o t a l o f 120 s e p a r a t e s u p e r c o n d u c t i n g pancakes a r e c o o l e d by f o r c e d flow of s u p e r c r i t i c a l h e l i u m . The a c t i v e s e n s o r s o f t h e s y s t e m a r e a m u l t i p l e quench d e t e c t o r . 1 3 thermometers and two l e v e l s e n s o r s i n t h e h e a t e x c h a n g e r s . T h e s e s i g n a l s a r e c o m p l e t e l y s u f f i c i e n t f o r t h e e l e c t r o n i c h a r d w a r e c o n t r o l f u n c t i o n s f o r cooldowrl, s t e a d y s t a t e and s a f e t y modes. The o n l y c o u p l i n g t o t h e h i g h l e v e l m i c r o p r o c e s s o r - c o n t r o l o f t h e f u l l y a u t o m a t i c t h e r a p y s y s t e m i s r e p r e s e n t e d by s e t t i n g t h e v a l u e s f o r t h e c u r r e n t s u p p l y f o r t h e magnets. The e u r o p e a n c o n d u c t o r t e s t f a c i l i t y SULTAN is e q u i p p e d w i t h a c o m p l e t e l y au tomated p r o c e s s corlt r o l s y s t e m h a n d l i n g cooldown, v a r i a b l e p a r a m e t e r s t e a d y s t a t e and a b o r t e d o p e r a t i o n modes. A s e p a r a t e d a t a a c q u i s i t i o n s y s t e m d e l i v e r s raw d a t a o r c a l i b r a t e d r e s u l t s on s c r e e n , t a p e o r a s hardcopy i n c l u d i n g g r a p h s r e a d y f o r p u b l i c a t i o n . The m i c r o p r o c e s s o r c o n t r o l l e d 1.4 kbl SULTAN- r e f r i g e r a t o r (SULZER) i s a b l e t o r e s t a r t a u t o m a t i c a l l y a f t e r a mains f a i l u r e .

The MAGCOOL s y s t e m f o r ISABELLE has an i n p u t / o u t p u t g e a r d r i v i n e 178 v a l v e s , c o n t r o l l i n g 38 d i r e c t d i g i t a l c o n t r o l l o o p s and r e a d i n g more t h a n 100 a n a l o g i n p u t s w i t h d i s p l a y a c c o m p l i s h e d t h r o u p h a c o l o r g r a p h i c s t e r m i n a l /11/.

The LCTF (Large C o i l T e s t F a c i l i t y ) I n s t r u m e n t a t i o n System /12/ w i l l h a n d l e a b o u t 1400 i n p u t s and 700 o u t p u t s f o r c o n t r o l w i t h 850 a d d i t i o n a l a n a l y t i c d a t a a c q u i s i t i o n c h a n n e l s and r e p r e s e n t s t h e l a r g e s t c o i l i n s t r u m e n t a t i o n s y s t e m a t p r e s e n t .

4 . QUhiCII PROTECTION

I n t h e l a r g e s t c o i l s y s t e m s p r e s e n t l y u n d e r c o n s t r u c t i o n o r o p e r a t i o n hundreds of I ~ l e g a j o u l e s have t o be s a f e l y dumped i n c a s e of emergency. The i m p o r t a n c e of a b s o l u t e r e l i a b i l i t y of t h e c o r r e s p o n d i n g s a f e t y s y s t e m c a n n o t be - o v e r e x a g g e r a t e d . S e l f - i n d u c t i v e b r i d g e s were r e l i a b l y u s e d f o r quench d e t e c t i o n i n most of t h e o p e r a t i o n a l s y s t e m s on s i n g l e c o i l s . With i n c r e a s i n g s t o r e d e n e r g y t h e c o r r e s p o n d i n g h i g h e r r e q u i r e m e n t s on r e l i a b i l i t y c o u l d o n l y be f u l f i l l e d by r e d u n d a n t m u l t i p l e b r i d g e d e t e c t o r s / I ? / . I n l a r g e m u l t i c o i l s y s t e m s w i t h a s s y m e t r i c c o u p l i n g s i t u a t i o n s r e d u n d a n t d e t e c t o r s y s t e m s have t o be u s e d b a s e d on a c o m b i n a t i o n o f s e l f - and m u t u a l - i n d u c t a n c e b r i d g e s i n c l u d i n g p o s s i b l y pick-up and Rogowski c o i l s /14/, /15/.

JOURNAL DE PHYSIQUE

5. FINAL REMRKS

A c t u a l problem a r e a s seem t o be t h e f o l l o w i n g :

- r e l i a b l e s t r a i n s e n s o r s i n h i & m a g n e t i c f i e l d

- vacuum m o n i t o r i n g i n v a r i a b l e f i e l d d e v i c e s

- two p h a s e rnassf low i n h e l i u m

- p r e s s u r e and f l o w i n s u p e r f l u i d

- r o t o r s i g n a l t r a n s m i s s i o n

- quench d e t e c t i o n i n p r e s e n c e o f e x t e r n a l d i s t u r b a x e e s - r a d i a t i o n dan;age i n low t e m p e r a t u r e s e n s o r s

Some i n t e r e s t i n g developrnents a t p r e s e n t a r e o f e x p e c t e d i r o n ; t h e a r e a of "cold e l e c t r o n i c s " ( a m p l i f i e r s and multiplexer) s i m p l i f y i n g s i & a l c o n d i t i o n i n g and t r a n s m i s s i o n .

A s a d e s i g n e r o f f o u r l a r g e r o u t i n e l y o p e r a t i n g s y s t e m s w i t h m u l t i r c e ~ a j o u l e c o i l s and w i t h kWatts o f r e f r i g e r a t i o n l e t me c l o s e i n s t e a d o f a c o n c l u s i o n w i t h two remarks t o c o i l s y s t e m d e s i g n e r s :

- No advanced i n s t r u m e n t a t i o n s y s t e m , however s o p h i s t i c a t e d , j u s t i f i e s a s a c r i f i c e i n s i m p l e , s o u n d l y e n g i n e e r e d c o i l d e s i g n w i t h a h i g h d e g r e e e o f i n t r i n s i c s a f e t y .

-

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