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A D.C. QUADRUPOLE 7T TEST FACILITY
J. de Reuver, H. Steffens, L.J.M. van de Klundert
To cite this version:
J. de Reuver, H. Steffens, L.J.M. van de Klundert. A D.C. QUADRUPOLE 7T TEST FACILITY.
Journal de Physique Colloques, 1984, 45 (C1), pp.C1-813-C1-816. �10.1051/jphyscol:19841166�. �jpa-
00223640�
JOURNAL DE PHYSIQUE
Colloque C l , suppl6ment au no 1, Tome 45, janvier 1984 page CI-813
A D ,C a QUADRUPOLE 7T
TEST
F A C I L I T YJ.L. de Reuver, H.A. Steffens and L.J.M. van de Klundert
Twente V n i o e r s i t y of TeehnoZogy, Department of Applied Physics, P.O. Box 217, 7500 AE Eizschede, !The NetherZands
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On presente des informations detaillees sur la conception et la rea- lisation d'un banc d'essais pour cdbles, avec des courants de 20 kA.Abstract
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Detailed information on the concept and construction concerning a new type of test facility for cables up to 20 k~ is presented.INTRODUCTION
Recent development of superconducting high current cables needs a larger high field testfacilitydesign. Present facilities usually consist of a solenoid or a split pair magnet. In both cases ambivalentcies often arise, for an optimal combination of test space, magnet volume and interchangability of the testcable is hard to achieve. Con- sidering the above mentioned items a new type of testfacility has been developed at the Division of Industrial Application of Superconductivity at Twente University.
THE CONCEPT
The D.C. quadrupole 7T magnet consists of two coaxial solenoids carrying current in opposite direction. The available testvolume has the shape of a torus with a large diameter of 200 mm and a small diameter of 30 to 70 mm according to the gap between the two coils (see Fig. 1).
Fig. 1
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Magnet configuration.AS a take off the diameter of 200 mm is chosen providing us a testlength of 600 Calculations of the field show that the diameter where the maximal field occurs equals this mean diar2eter in a good approximation. A secondconstraint is the volume of superconducting wire which is at our disposal to wind the magnet. This limitation
Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:19841166
C1-814 JOURNAL
DE
PHYSIQUEi s mainly a m a t t e r of budget. An-optimal geometry, concerning width and h e i g h t of t h e c o i l ' s c r o s s - s e c t i o n , c a n b e found, independent of t h e superconducting w i r e ' s q u a l i t y o r t h e wanted f i e l d magnitude, i f t h e r a t i o of t h e f i e l d i n t h e t e s t volume and t h e maximum f i e l d a t t h e windings h a s a maximumfora given g a p d i s t a n c e . I n c a s e of t h i s quadrupole geometry two maxima occur. These maxima and t h e o b t a i n e d t e s t f i e l d f o r a c e r t a i n combination of h e i g h t and width of t h e c r o s s - s e c t i o n a g a i n s t t h e g a p d i s t a n c e a r e given i n Fig. 2.
Together w i t h this minimum t h e f i e l d r a t i o a n d t h e g a p d i s t a n c e a t which i t o c c u r s a r e f i x e d . A combination of t h e s e g r a p h s o f f e r s u s equi-width and - h e i g h t l i n e s ( F i g . 3 ) . They can b e extended w i t h equivolume l i n e s . Every c r o s s i n g i n t h i s p l o t corresponds with a f i e l d r a t i o and homogenity. Table 1 can be deduced i n t h i s way.
Fig. 2
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Determination of minimum magnetic f i e l d a t t h e windings and t h e corresponding t e s t f i e l d magni- t u d e f o r a c e r t a i n shape f o r t h e c r o s s - s e c t i o n .1+2: maximum f i e l d s a t t h e windings.
3: f i e l d i n t h e testuolume.
c u r r e n t d e n s i t y 125 ~ / m m ~ . d: gap d i s t a n c e .
4 5 .
-
I--
7 4 . 0 .
3.5
3.0
25.
Fig. 3
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Optima f o r a given width ( b )Vz23 and h e i g h t ( h i n mm) o f t h e c r o s s -
. s e c t i o n of t h e c o i l . Equivolume ( v
i n dm3) l i n e s a r e given a s w e l l .
2 0 30 40 50 60
d Imml
width
-iio-- ---
hg-ight--- voiu_rne_ ---
PCP---
---homogen&:z---- f l?ir!ra_t&o--
i n c r e a s e c o n s t a n t i n c r e a s e d e c r e a s e i n c r e a s e i n c r e a s e c o n s t a n t i n c r e a s e i n c r e a s e d e c r e a s e i n c r e a s e i n c r e a s e 3
1
i n c r e a s e d e c r e a s e c o n s t a n t i n c r e a s e d e c r e a s e d e c r e a s e 4 i n c r e a s e d e c r e a s e i n c r e a s e c o n s t a n t i n c r e a s e c o n s t a n t Table 1-
I n f l u e n c e on homogenity and f i e l d r a t i o i f t h e t e s t f i e l d i s i n c r e a s e d by changing a r e l e v a n t parameter combination under o p t i m a l geometry c o n d i t i o n s .No. 1 and 2 show t h a t any change i n a width o r h e i g h t t o i n c r e a s e t h e volume f o r h i g h e r f i e l d m a g n i t u d e s , r e f l e c t s i n a d e c r e a s e of t h e g a p d i s t a n c e under optimal geometry c o n d i t i o n s . No. 3 shows t h a t l e s s f a v o u r a b l e c o n d i t i o n s a r i s e i f t h e volume i s k e p t c o n s t a n t and t h e combination width-height i s v a r i e d i n favour of t h e width.
The optimum moves i n t h e d i r e c t i o n of l a r g e r gaps which can be c o n c i l i a t i n g . From no. 4 we can s e e t h a t while s c a l i n g up w i t h keeping t h e g a p d i s t a n c e c o n s t a n t t h e f i e l d r a t i o w i l l b e c o n s t a n t a s w e l l , i n good approximation however, a s h i f t o c c u r s concerning width and h e i g h t i n favour of t h e width.
I n most p r a c t i c a l c a s e s t h e homogenity demand i s l e s s s t r i n g e n t because t h e volume of superconductor i n t h e magnet exceeds t h e t e s t v o l u m e c o n s i d e r a b l y . The main d e t a i l s of t h e f i n a l concept a r e given i n Table 2.
Table 2. - Construction d e t a i l s . M u l t i f i l a m e n t a r y wire: NbTi/Cu
Diameter: .7 mm w i t h o u t - 7 5 mm with i n s u l a t i o n Number of f i l a m e n t s : 132
CN : S.C. : 2.5 : 1
S h o r t sample c u r r e n t s : 6T:120A, 7T:98A, 8T:80A Number o f windings: 25000
Impregnant: MY 740/MY906/~~ 062 100/80/.2 F i l l e r : 60 weight % Quartz c7 < 4 0 um T o t a l mass: 200 kg
Item 5 0 70 mm
... GSEI-~!? ...
T e s t fieldmaximum 7.0 5.3 4.4 T
F i e l d r a t i o .93 .68 .55
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F i e l d - c u r r e n t r a t i o 7 5 55 45 mT/A
S e l f inductance (22.2 H p e r c o i l ) 31 34 36 H
Load energy 156 171 182 kJ
Mutual f o r c e 900 600 500 kN
Homogenity R = 10 m 2 2 2 ,
R = 2 0 m 8 8 8 %
THE CONSTRUCTION
Both c o i l s a r e made of m u l t i f i l a m e n t a r y wire. They a r e wound on aluminium c y l i n d e r s . T h i s c o n s t r u c t i o n m a t e r i a l i s used f o r t h e house t h a t surrounds t h e c o i l s a s w e l l . The w i r e i s wet-wound w i t h an e p o x y , f i l l e d w i t h q u a r t z . Good r e s u l t s with vacuum impregnation a r e n o t l i k e l y because t h e f i l l i n g f a c t o r wire-impregnant i s chosen t o be very high. The windings a r e i n c l o s e c o n t a c t and no p a t h f o r t h e f i l l e d epoxy w i l l be f r e e . Around t h e o u t e r w i n d i n g s g l a s s f i b e r , a s an i n essence redundant r e i n f o r c e m e n t , i s wound. To a v o i d e l e c t r i c a l c o n t a c t between house and w i r e an i n s u l a t o r of GI1 m a t e r i a l i s a p p l i e d . The aluminium house c o n s t r u c t i o n t h a t w i l l b a l a n c e t h e expanding f o r c e s of 900 k N a s w e l l a s t h e c o i l w i t h a maximum f o r c e i n a x i a l d i r e c t i o n of 1400 kN needs s p e c i a l c a r e . The l a t t e r f o r c e i s d i s t r i b u t e d
JOURNAL DE PHYSIQUE
r a t h e r homogeneous which i s a p r o p e r t y of t h e c o i l c o n f i g u r a t i o n . The f o r c e s i n t h e r a d i a l d i r e c t i o n a r e r e l a t i v e l y s m a l l compared with t h e s e azimuthal ones. T e s t s t o examine i f t h e c o i l can s t a n d t h e s e f o r c e s on a t e s t c o i l wound w i t h copper w i r e have ,been f i n i s h e d s u c c e s f u l l y .
THE QUENCH BEHAVIOUR
I n emergencies t h e e n t h a l p y of t h e copper m a t r i x i s s u f f i c i e n t t o keep a maximum h e a t r i s e b e l o w 100 K r e g a r d i n g a w o r s t c a s e . Some i n t e r e s t i n g f e a t u r e s a r e t h e propagation t h a t can b e c a l c u l a t e d t o be 1 m / s ( / I / ) and t h e matching o v e r a l l time c o n s t a n t o f 1 s e c . C a l c u l a t i o n s on t h e worst c a s e g i v e a t o p v o l t a g e of 4000 V r e s - p o n s i b l e f o r t h e d i s s i p a t i o n . F a s t propagat-ion g u a r a n t e e s t h e p r e v e n t i o n of high g r a d i e n t s i n t h e r e s i s t a n c e a l o n g t h e windings which would l e a d t o e l e c t r i c a l outburn damage. E v i d e n t l y good i n s u l a t i o n p r o v i s i o n i s taken c a r e f o r . A dump r e s i t o r of 20 D d e c r e a s e s t h e t o p v o l t a g e down t o 3000 V. A h i g h l y r e s i s t i v e p e r s i s t e n t mode s w i t c h i s r e q u i r e d . I t has t o d e a l w i t h a v o l t a g e o f 1000 V f o r a s h o r t time. The dumped energy w i l l o n l y b e 1/3 of t h e t o t a l l o a d energy. The tempe- r a t u r e r i s e w i l l be 75 K now. I n t h e s e c a l c u l a t i o n s no assumptions on t h e c o i l house behaviour have been included.
DISCUSSION
The manner t o o b t a i n an optimum i n t h e v o l u m e r a t i o testspace-magnet,combines t h e advantage of t h e i n t e r c h a n g a b i l i t y of a s p l i t p a i r magnet and t h e r e l a t i v i l y h i g h e r
fieldratio testspace-coilwindings o f a s i n g l e s o l e n o i d . I n t h e l a t e r c a s e f o r con- v e n t i o n a l s i t u a t i o n s t h i s r a t i o w i l l be h i g h e r .
The c o n s t r u c t i o n i s simple. Many a s p e c t s , l i k e manufacture o f t h e c o i l s , c o o l down a n d q u e n c h p r o t e c t i o n can be t r e a t e d i n t h e approved way.
A s p e c i a l item is t h e n e g a t i v e c o u p l i n g of t h e two c o i l s . This f a c t d i m i n i s h e s t h e s e l f i n d u c t a n c e a n d t h e r e l a t e d load energy. However, t h e c o n s t r u c t i o n s complexity i n c r e a s e s because of t h e induced expanding f o r c e s . Surveying t h i s , t h e good t r a i n i n g behaviour of s o l e n o i d s i s expected t o b e p r e s e r v e d .
The n e g a t i v e coupling, mentioned above, g u a r a n t e e s t h e absence of i n d u c t i v e coupling w i t h t h e t e s t s a m p l e . The magnet is t h e r e f o r e very a p p r o p r i a t e f o r t h e i n v e s t i g a t i o n of a . c . a p p l i c a t i o n s .
A f u t u r e o p t i o n i s an e x t e n s i o n w i t h a cryogenic 20 kA c u r r e n t source. The low f i e l d s c a t t e r background is t h e r e f o r e favourable. To complete t h e f a c i l i t y i n t h i s way i s s e t an aim f o r t h e n e a r f u t u r e . Of minor importance i s t h e p o s s i b i l i t y t o use t h e magnet f o r high g r a d i e n t f i e l d t e s t i n g a s w e l l .
CONCLUSION
Applying a simple quadrupole geometry, a t e s t f a c i l i t y can be developed having t h e b e n e f i t of a high r a t i o of t h e f i e l d i n t h e t e s t v o l u m e and t h e maximum f i e l d a t t h e windings. A s themagnetvolume compared w i t h t h e achieved t e s t v o l u m e c a n be k e p t small a low budget t e s t f a c i l i t y f o r high c u r r e n t c a b l e s can be a f f o r d e d . Other advantages of t h i s system, i f d e s i r e d , a r e t h e e a s y i n t e r c h a n g a b i l i t y of t h e samples and t h e non-inductive coupling between t h e sample and magnet. Summarizing t h e b e n e f i t s t h e f p t u r e a p p l i c a t i o n of t h i s t e s t f a c i l i t y l o o k s promising.
REFERENCE
1. Hagedorn, D . J . , T h e s i s Bochum (W.73).
