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ALTERNATIVES AND IMPROVEMENTS FOR SUPERCONDUCTING DIPOLE COILS FOR HERA
G. Horlitz, H. Kaiser, G. Knust, K.-H. Mess, S. Wolff, P. Schmüser, B. Wiik
To cite this version:
G. Horlitz, H. Kaiser, G. Knust, K.-H. Mess, S. Wolff, et al.. ALTERNATIVES AND IMPROVE- MENTS FOR SUPERCONDUCTING DIPOLE COILS FOR HERA. Journal de Physique Colloques, 1984, 45 (C1), pp.C1-259-C1-262. �10.1051/jphyscol:1984152�. �jpa-00223708�
ALTERNATIVES AND IMPROVEMENTS FOR SUPERCONDUCTING DIPOLE COILS FOR HERA
G. Horlitz, H. Kaiser, G. Knust, K.-H. Mess, S. Wolff, P. schmi;serr and B.H. wiikrr
DESY, Hamburg, F. R. G.
'II. I n s t . fiir ExperimentaZphysik, Univ. Hamburg, F. R. G.
++ II. Inst. f u r ExperimentaZphysik, Univ. Hamburg and DESY, Hamburg, F.R.G.
& s d - L a bobine d'un aimant de 1 m de long a B t & bridge avec des c o l l i e r s en aluminium. Les performances atteintes sont l e s &es qu' avec des c o l l i e r s d'acier inoxydable. Jusqu' a prgsent aucun e f f e t de fatigue n'a &Ye observg apr6s 5000 cycles de montk de courant.
Plusieurs aimants de 1 m e t de 6 m ont Bt6 construits avec des cales longitu- dinales dans chacune des 2 bobines, ce qui Blimine l e s contributions 14- polaires e t 18-polaires.
Abstract - A 1 m long dipole c o i l has been clamped with aluminum collars. The sane performance has been reached a s with stainless s t e e l collars. Up to now no fatigue effects have been observed a f t e r 5000 ramping cycles. Several 1 m and 6 m long c o i l s have been b u i l t with longitudinal wedges i n both c o i l layers which eliminate 14-pole and 18-pole contributions.
TEST OF ATXNDWM COLLARS
Our prototype dipole c o i l s b u i l t so f a r have been clamped with stainless s t e e l collars similar to those used a t Fermilab. The main task of these collars is t o define the c o i l I
geometry with a high precision and to support the conductors against the very large magne- t i c forces. A cross section of the f i r s t four prototype c o i l s i s shown i n Fig. 1. The magnetic forces a t 4.53 T are plotted in Fig. 2 as a function of conductor number.
Close t o the mid-plane the forces are mainly radial with a net ccinpnent i n the outward direction. A t the c o i l edges the forces have a large azimuthal component directed towards the mid-plane which tends to w e the c o i l edges away from the key angles of the collars. Since such a conductor motion m y lead to a quench the c o i l package has t o be precornpressed so t h a t the mechanical forces are well above the highest magnetic forces.
For the layout of the collars the magnetic forces of Fig. 2 were increased by a safety
factor of 1.5 and it was required t h a t the Fig. 1 - Coil cross section of f i r s t remaining catpressing force had t o be prototypes (quadrant, uniform current 2 - 1 o5 N/m a t the edges of both c o i l layers. &stributlon) . Inner c o i l layer (1 ) ,
The mechanical precompression a t helium tern- outer c o i l layer ( 2 ) , GI1 layer ( 3 ) , perature is then 6.4 . 105 N/m a t the edge c o i l insulation (4) , stainless s t e e l of the inner c o i l layer and 3.7 - 1 o5 N/m a t collars (5) , longitudinal rods (6) ,
the edge of the outer layer. (These forces R~ = 37.50 m, R~ = 47.76 m, R3 = have been computed by G. Meyer, DESY.) The 48.25 m, Rq = 58,51 m, 9 1 = 71.89501 precompression needed a t r m temperature i s q2 = 35.1770
Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:1984152
JOURNAL DE PHYSIQUE
I Icood. no.)
Fig. 2 - Magnetic forces a t nominal cur- rent f o r individual conductors. Azimuthal forces in inner c o i l layer ( I ) , azimuthal forces i n outer layer ( 2 ) , both directed tmards the mdian plane, radial forces i n inner c o i l layer ( 3 ) , directed out- wards, radial forces i n outer c o i l layer
( 4 ) , directed inwards.
Fig. 3 - Straight section harmonics of aluminum collared c o i l without iron yoke. Normal harmonics b2 (quadrupole) and b3 ( s e x t u p l e ) and skew harmonics a2 and a3 versus current before cyc- l i n g (e) and a f t e r 5373 cycles between 3000 A and 6000 A (x) .
about 13% higher i f the collars a r e made from stainless s t e e l whose thermal shrinkage between 300 K and 4 K i s smaller than t h a t of the c o i l package (3 -
a s compared to about 3.3 . 1 0-3) .
A s these large forces may lead to a creep of the Kapton insulation of the cable w e have considered t o use aluminum a s a collaring material instead. It has a thermal contraction of 4.1 . and therefore requires a 37% lower precampression a t 300 K than a t 4 K. Moreover the costs a r e considerably lower. The lower modulus of e l a s t i - c i t y and possible fatigue may be a disadvantage compared t o stainless steel. Alumi- num clamps of 4 m thickness were made from a high yield strength alloy (Al Zn 4.5 Mg 1) using the same stamping d i e a s f o r the stainless s t e e l clamps. A I m long dipole c o i l (1S2) which had been tested with stainless s t e e l collars previouslyl) was disassembled and equipped with the aluminum clamps. Since the geometry of t h i s c o i l had been matched t o the thermal shrinkage of stainless s t e e l the c o i l was some- what oversized f o r the aluminum collars. For t h i s reason it was not yet possible t o realize the lower precompression a t room temperature.
The c o i l was tested in a v e r t i c a l bath cryostat. No training steps were observed and the same currents were reached a s with stainless s t e e l collars. The maximum quench current was 7156 A a t 3.93 K corresponding t o 5.16 T i n the c o i l center and 5.60 T a t the conductor. The quadruple and s e x t u p l e coefficients a r e shown in Fig. 3 a s a function of current. Except f o r the well-known hysteresis, the sextupole has no significant current dependence up t o 7000 A which indicates t h a t the higher d e f o m - tion of the aluminum c o l l a r s has l i t t l e influence on the f i e l d quality. To study fatigue effects, the current was cycled 5000 times between 3000 A and 6000 A. The
before.
The t e s t s done so f a r with the aluminum collars have been quite promising and justify further investigations.
THE NEW COIL CONCEPT
The f i r s t two 6 m long prototype c o i l s (6S1 and 652) were b u i l t with 32 turns i n the inner and 19 turns i n the outer c o i l layer and uniform cable distribution in the c o i l (Fig. 1 ) . The theoretical harmonics in such c o i l s with and without iron yoke (inner radius 113.5 nun) are l i s t e d i n Table I. The c o i l angles have been chosen t o yield vani- shing s e x t u p l e and d e c a p l e terms. The relatively high 14- and 18-poles, however, are an inherent feature of t h i s kind of coil.
Beam tracking calculations have shown t h a t Fig. 4 - Improved coil configuration the beam acceptance i s reduced due t o the (quadrant) . Inner c o i l layer (1 ) ,
strength of these harmonics. An improved outer c o i l layer ( 2 ) , longitudinal c o i l configuration i s shown i n Fig. 4. There wedges (3) , GI 1 layer ( 4 ) , c o i l are now 32 turns in the inner and 20 turns insulation ( 5 ) , stainless s t e e l col- i n the outer c o i l layer. The wedges made l a r s (6) , longitudinal rods ( 7 ) ,
from glass fiber reinforced epoxy (GI 1 ) R1 = 37.50 nun, R2 = 47.76 nun, R3 = b e h i n d t h e f o u r t h t u r n i n e a c h l a y e r (coun- 48.25mn,R4=58.51m,cP1 = 7 6 . 7 4 O , t e d f r o m t h e k e y a n g l e ) r e d u c e t h e 1 4 - a n d ~ 2 = 4 4 . 1 I 0 , c c l = 4 . 8 4 0 , a 2 = 4 . 8 5 0 18-poles practically t o zero. Setting the
d e c a p l e t o + 2 - 10-4 gives an additional improvement and leads t o a f i e l d inhomoge- i t y i n the horizontal plane of better than
+ 1 (Fig. 5 ) . Several
A B/ 1 m and 6 m long prototype
Bo !! c o i l s of t h i s type have been
5 ~ 1 0 - ~ - .
-5~16~:
1 built. So f a r the f i e l d qua- l i t y has been tested a t room
/'-\ temperature only (see Table
I ) . The 14- and 18-ples are
i quite small. According t o our
experience with other c o i l s
2 we expect similar values in
/ the superconducting s t a t e .
>
1 7 ~ . \3
\ 4 x [ c m l A ~ O ~ ~ s
We would l i k e t o express our
2 " gratitude t o a l l technicians, engineers and s c i e n t i s t s who have contributed t o the design, fabrication and t e s t s Fig. 5 - Field homogeneity in the horizontal plane. of these magnets.
Coil configuration with uniform current distribu- tion, b3 = b5 = 0, b7 = 13.9, bg = - 12.0 ( I ) , with longitudinal wedges i n inner and outer layer, b3 =
bg = 0, b2 = - 0.6, bg = - 0.3 ( 2 ) , with longitudi- nal wedges, b3 = 0, b5 = 2.0, b7 = - 1.0, bg = -0.2
(3) , a l l harmonics in units of 10-4.
JOURNAL DE PHYSIQUE
Table I - Straight section harmonics at room temperature (at r = 2.5 cm relative to Bo)
1) G. Horlitz, H. Kaiser, G. Knust, K.-H. Mess, P. Schmiiser, B. H. Wiik, S. Wolff
"Performance of 1 m long/75 nun Bore Superconducting Prototype Coils for HEFA", Proc.
Particle Acc. Conf., Santa Fe, 1983, D E E Trans. Nuc. Sci. el 3390 (1 983) ,
preprint DESY 83-020, March 1983 harmonic
no- 1 2 3 4 5 6 7 8 9 10 1 1
measured value at room t-rature coil 6S3 without yoke bnxl o4 +XI o4
10000. -
-3.2 -0.2 2.1 -0.6
-0.1 2.0
0.3 -0.6
0.3 0.4
-0.2 -0.2
0.0 0.2
-0.3 0.0 -0.1 0.1
-0.3 0.0
design value (longitudinal wedges) design value
(uniform cable distr.)
with yoke bnxl 04
10000.
0.
0.
0.
2.
0.
-1.
0.
-0.2 0.
-0.3 with yoke
h x~ o4
10000.
0.
0.
0.
0.
0.
13.4 0.
-11.9 0.
3.2
without yoke
&XI 04 10000.
0.
-1 .O 0.
2.2 0.
-1.1 0.
-0.3 0.
-0.3 without yoke
kxl 04 10000.
0.
-1 .I 0.
0.
0.
14.9 0.
-13.2 0.
3.5
