THE LEP MAGNET SYSTEM

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THE LEP MAGNET SYSTEM

L. Resegotti

To cite this version:

L. Resegotti. THE LEP MAGNET SYSTEM. Journal de Physique Colloques, 1984, 45 (C1), pp.C1- 233-C1-239. �10.1051/jphyscol:1984147�. �jpa-00223703�

J O U R N A L D E PHYSIQUE

Colioque C1, suppl6ment au no I, Tome 45, janvier 1984 page C 1-233

THE LEP MAGNET SYSTEM L. Resegotti

LEP Division, C . E. R. N . , 1211 Geneva 23, Switzerland

R6sum6

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velopp6es dans un souci d86conomie e t d 1 e f f i c a c i t 6 , notamment pour l e s d i p c l e s e t l e s l e n t i l l e s magngtiques, q u i sont t r s s nombreux e t d o i v e n t E t r e p r o d u i t s

i une cadence 61 ev6e, f o n t 1 'o b j e t d'une p r 6 s e n t a t i o n p l u s d 6 t a i l l 6e, accom- pagn6e des r 6 s u l t a t s acquis 2 l ' a i d e des prototypes d'6tude. Les s o l u t i o n s adopt6es pour l e c o n t r c l e de production e t pour l e s mesures magn6tiques sont e n s u i t e discut6es. Le papier se termine p a r un apersu du programme de f a b r i c a - t i o n e t d ' i n s t a l l a t i o n .

A b s t r a c t

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The s o l u t i o n s adopted f o r s e r i e s p r o d u c t i o n c o n t r o l and f o r t h e magnetic meas- urements a r e reported. The expected schedule o f manufacturing and i n s t a l l a t i o n i s mentioned.

I

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LEP, t h e Large Electron-Positron c o l l i d e r under c o n s t r u c t i o n a t CERN 111, has a c i r - cumference o f 26.659 km and i s l o c a t e d i n an underground tunnel i n t h e r e g i o n between t h e piedmont o f t h e J u r a and the Geneva a i r p o r t , s t r a d d l i n g the border between France and Switzerland. The f i r s t phase, which i s now authorized, w i l l i n v o l v e t h e construc- t i o n o f t h e complete magnet and vacuum systems and s u f f i c i e n t radiofrequency t o s t o r e beams o f e l e c t r o n s (e-) and p o s i t r o n s (e4) up t o an energy of between 50 and 60 GeV. The p o s s i b l e f u t u r e a d d i t i o n o f more equipment would enable the storage o f beams o f h i g h e r energies up t o a maximum o f 125 GeV b u t such a d d i t i o n s would r e q u i r e f u r t h e r a u t h o r i z a t i o n fromtheCERN Member States.

The tunnel [ 2 1 l i e s i n a plane i n c l i n e d by about 1.5 % w i t h r e s p e c t t o t h e h o r i z o n t a l and i t s average depth i s about 90 m. It c o n s i s t s o f e i g h t arcs, where i t has a d i a - meter o f 3.76 m (Fig. l ) , i n t e r l e a v e d w i t h e i g h t s t r a i g h t sections. C o l l i s i o n s o f

f o u r e l e c t r o n bunches and f o u r p o s i t r o n bunches may be obtained and e x p l o i t e d f o r ex- periments a t e i g h t " i n t e r a c t i o n p o i n t s " i n the middle o f t h e s t r a i g h t sections. How- ever, o n l y f o u r experimental areas, a t t h e even points, w i l l be equipped i n phase l.

Electrons and p o s i t r o n s w i l l be i n j e c t e d i n t o t h e LEP main r i n g a t an energy o f about 20 GeV from a cascade o f machines [3], c o n s i s t i n g o f a l i n e a r a c c e l e r a t o r v i t h con- v e r s i o n t a r g e t ( L I L ) and a 600 MeV+accumulation r i n g (EPA), f o l l o w e d by t h e e x i s t i n g PS and SPS, s u i t a b l y t u r n e d i n t o e- synchrotrons o f 3.5 GeV and 20 GeV energy, r e - s p e c t i v e l y . I n t h e main r i n g , the p a r t i c l e s w i l l r e c e i v e energy from RF c a v i t i e s operated a t about 352 MHz. I n phase 1, t h e c a v i t i e s w i l l be l o c a t e d i n t h e s t r a i g h t s e c t i o n s adjacent t o p o i n t s 2 and 6, and t h e i r i n p u t power w i l l be 16 MW. E l e c t r o n s and p o s i t r o n s w i l l c i r c u l a t e i n s i d e a vacuum chamber, made o u t mostly o f extruded aluminium p r o f i l e s [21, w i t h a main e l l i p t i c a l a p e r t u r e of

*

*

Cl-234 JOURNAL DE _PHYSIQUE

beams. The chambers i n t h e d i p o l e gaps a1 so have a p a r a l l e l channel f o r a continuous pump. A1 1 vacu- um chambers a r e coated w i t h a l a y e r o f l e a d o f a thickness v a r y i n g between 3 and 8 mm t o absorb most o f t h e synchrotron r a d i a - t i o n energy, thus p r o t e c t - : i n g t h e surrounding equip- ment. The o v e r a l l dimen- sions o f the chambers, p l u s t h e e x t r a clearance needed f o r bakeout, d e t e r - mine t h e p h y s i c a l aper- t u r e s o f t h e magnets, which a r e appreciably l a r g e r than t h e useful beam apertures.

Fig. 1

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The magnet system i n t h e LEP r i n g i s a separated-function s t r u c t u r e . The l i n e a r ma- c h i n e l a t t i c e c o n s i s t s o f t h e main dipoles, which a r e present o n l y i n t h e arcs, where they bend t h e t r a j e c t o r i e s o f t h e p a r t i c l e s i n t h e plane o f t h e machine, and the qua- drupoles, which focus t h e p a r t i c l e s towards t h e c e n t r a l o r b i t a l l along t h e circum- ference. The r e g u l a r l a t t i c e p e r i o d s i n t h e middle o f t h e a r c s a r e 79 m l o n g and con- t a i n two quadrupoles, r a d i a l l y f o c u s i n g and defocusing r e s p e c t i v e l y , o f 1.6 m magnet- i c length, and two bending magnets, each made o u t o f s i x equal cores, 5.75 m long, and having a t o t a l magnetic l e n g t h o f 35 m. I n t h e i n j e c t i o n regions, f r e e space f o r t h e i n j e c t i o n septa and k i c k e r s i s created by u s i n g s h o r t e r dipoles, w i t h t w i c e t h e magnetic f i e l d o f t h e others.

A t each end o f an arc, t h e r e i s a group o f s h o r t e r c e l l s , which have t h e f u n c t i o n o f suppressing t h e r a d i a l d i s p e r s i o n i n t h e s t r a i g h t sections o f t h e machine. One o f these c e l l s c o n t a i n s a two-core d i p o l e , f i v e a four-core d i p o l e and a l a s t one a spe- c i a l "weak d i p o l e " where t h e magnetic f i e l d has about one t e n t h o f t h e normal value, i n order t o lower t h e i n t e n s i t y and t h e energy spectrum o f t h e synchrotron r a d i a t i o n , f o r t h e p r o t e c t i o n o f t h e experiments.

The composition o f t h e main d i p o l e system i s summarized i n Table 1. A l l normal d i - poles a r e e x c i t e d by means o f l o n g bars made o f extruded hollow aluminium conductor, a l l connected i n s e r i e s i n s i t u t o form a s i n g l e powering c i r c u i t , e q u i v a l e n t t o one t u r n on each pole. This s o l u t i o n i s cheaper than t r a d i t i o n a l c o i l s and minimizes t h e space l o s t a t t h e j u n c t i o n s between cores. F i g u r e 2 shows a s i x - c o r e prototype. The d i p o l e s i n t h e i n j e c t i o n r e g i o n have m u l t i t u r n c o i l s and a r e separately powered.

The quadrupoles i n t h e "normal" l a t t i c e i n t h e arcs are d i v i d e d i n two f a m i l i e s , ho- r i z o n t a l l y focusing (F) and defocusing ( D l , r e s p e c t i v e l y : a l l members o f each f a m i l y a r e connected i n series. The quadrupoles i n t h e d i s p e r s i o n suppressors and i n the ac- c e l e r a t i o n regions, which are somewhat longer than those i n t h e normal l a t t i c e , a r e separately powered i n p a i r s , because t h e i r e x c i t a t i o n must be modulated t o o b t a i n the r e q u i r e d v a r i a t i o n o f t h e b e t a t r o n f u n c t i o n s .

A t t h e i n t e r a c t i o n p o i n t s , the transverse beam s i z e must be squeezed as much as pos- s i b l e t o increase t h e l u m i n o s i t y f o r t h e experiments: t h e g r o u p s . o f quadrupoles which lower l o c a l l y t h e values o f the amplitude functions BZ and Ox, w h i l e m a i n t a i n i n g t h e match w i t h t h e r e s t o f t h e focusing system o f the machine, a r e c a l l e d low-beta

Table 1

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*

i n s e r t i o n s . I n phase 1, s t r o n g low-beta i n s e r t i o n s w i l l e x i s t o n l y a t t h e even num- bered i n t e r a c t i o n p o i n t s , where experiments w i l l be mounted: t h e i r f r o n t elements w i l l be superconducting quadrupoles. The o t h e r elements o f these i n s e r t i o n s , as w e l l as a l l those o f t h e simple matching i n s e r t i o n s a t t h e odd numbered i n t e r a c t i o n p o i n t s , w i l l probably be b u i l t o u t o f "normal" and "long" quadrupoles, some o f which i n p a i r s . A l l these i n s e r t i o n quadrupoles w i l l have t o be replaced by s t r o n g e r ones a t machine energies above 65 GeV.

Element Main dipoles:

2-core dip01 es 4-core d i p o l e s 6-core dip01 es

Low f i e l d (4-core) d i p o l e s I n j e c t i o n r e g i o n d i p o l e s L a t t i c e quadrupol es:

regul a r c e l l s d.s. and RF c e l l s I n s e r t i o n quadrupol es:

i n f r o n t p a i r s i n back p a i r s superconduc ti ng Sextupol es :

SF SD

C o r r e c t i n g d i p o l es:

CH (horiz., i n a r c s ) CV (vert., i n a r c s ) CHA (horiz., i n d.s. + RF) CVA ( v e r t . , i n d.s. + RF) CHB (horiz., i n i n s e r t i o n s ) CVB ( v e r t . , i n i n s e r t i o n s ) Wigglers ( d i p o l e )

T i 1 te d quadrupol es

The c o r r e c t i o n o f the machine c h r o m a t i c i t y r e q u i r e s a number o f sextupole magnets.

There i s a sextupole near each quadrupole i n t h e normal arcs; those near t h e horizon- t a l l y focusing quadrupol es (sextupol es SF), where t h e d i s p e r s i o n f u n c t i o n i s 1 arger, are o n l y about h a l f as l o n g as those near the h o r i z o n t a l l y defocusing quadrupoles (sextupoles SD). They a r e grouped i n t h r e e f a m i l i e s o f each type, t h e members o f each f a m i l y being a l l powered i n series.

Maximum s t r e n g t h

B = 0.135 T B = 0.0135 T B = 0.135 T(.) B'= 9.7 Tm-I B1= 10.9 ~ m - l B ' = 10.9 ~ m - I ( ? ) B1= 9.7 Tm-l(*) B ' = 36 Tm-l( .) B"= 180 ~ m - ~ B"= 180 T w 2 B = 0.063 T B = 0.038 T B = 0.080 T B = 0.062 T B = 0.072 T

*

B = 0.132 T

*

B+= 1.00 T B.= 0.40 T B1= 2.0 Tm-I

*

The l a s t widespread elements o f t h e magnet system a r e the d i p o l e s f o r closed o r b i t c o r r e c t i o n . I n LEP, t h e c o r r e c t o r s a r e short, i n d i v i d u a l l y powered dipoles. It was found unadvisable t o use back-leg windings on t h e main dipoles, as i s done i n o t h e r machines, because o f t h e excessive i n f l u e n c e t h a t t h e h y s t e r e s i s c y c l e o f t h e main magnets would have on t h e c o r r e c t i o n , p a r t i c u l a r l y near i n j e c t i o n energy.

Number

16 80 488 16 24 488 2 56

32(?) 32(*)

8 ( . ) 248 2 56 168 176 88 88 8 16

f

32 *

Ima x

5700 A

625 A

525 A

300 A

300 A('?) 525 A(?) 1800 A(*)

360 A

360 A

2.5 A 2.5 A 5.0 A 5.0 A 7.0 A

*

7.0 A

*

550 A

55 A 55 A

*

Magnetic 1 ength

11.66 m 23.34 m 35.01 m _{23.34 m}

1

5.87111 1.60 m 2.00 m 2.00 m(?) 1.60 m($) 2.00 m(.) 0.40 m 0.76 m 0.48 m 0.54m 0.48 m 0.54111 0.50 m

*

0.50 m

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0.74 m 1.85 m 0.50 m *

Cl-236 JOURNAL D E PHYSIQUE

Fig. 2

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Other elements o f t h e LEP magnet system e x i s t i n smaller numbers, mainly near t h e i n t e r a c t i o n regions. They are t h e t i l t e d quadrupoles, which a r e needed t o a d j u s t t h e c o u p l i n g between t h e two p r i n c i p a l b e t a t r o n planes, and the w i g g l e r dipoles, t o c o n t r o l the beam emittance and t o reduce t h e damping time.

The composition o f t h e magnet system i s shown i n Table 1.

111

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The 3304 d i p o l e cores, each 5.75 m long, produce bending f i e l d s over more than 70 % of t h e machine circumference. T h e i r cost, however, represents o n l y 3.5 % o f t h e t o t a l m a t e r i a l investment f o r LEP, thanks t o t h e use o f stacks o f w i d e l y spaced lamina- t i o n s , f i l l e d and bonded by cement mortar, so t h a t the s t e e l occupies o n l y 27 % o f t h e c o r e length. The cores are k e p t under compression by pre-tensioned rods and thus behave as pre-stressed concrete beams, which a r e more r i g i d than conventional welded stacks. They are a l s o h a l f as heavy. This c o n s t r u c t i o n technique, which has been de- veloped a t CERN s p e c i a l l y f o r LEP, where the bending f i e l d s a r e very low, has been presented i n o t h e r conferences [4,51 and i s o n l y r e c a l l e d here.

The 1.5 mm t h i c k l a m i n a t i o n s a r e p r e c i s i o n punched from decarburized s t e e l sheet, which i s very d u c t i l e , besides having the r e q u i r e d magnetic p r o p e r t i e s , i.e. low c o e r c i v i t y and h i g h permeability. The punching d i e can thus a l s o press o u t s u i t a b l e

i n d e n t a t i o n s o f 2 mm, which, when placed back-to-back, ensure t h e r e q u i r e d spacing of 4 mm between adjacent l a m i n a t i o n s i n t h e stack. F i g u r e 3 shows i n some d e t a i l t h e f i n a l s t r u c t u r e and transverse dimensions o f t h e cores.

The r e q u i r e d tolerances on geometry and mechanical s t a b i l i t y o f t h e cores have been achieved w i t h adequate margins i n model prototypes. Thanks t o t h e use o f a p p r o p r i a t e m o r t a r compositions, t h e shrinkage i n l e n g t h a t d r y i n g i s about 2 mm and r a t h e r re-

producible: t h e small d i f f e r e n c e s can be compensated f o r by a d j u s t i n g t h e spacing o f t h e two cores i n each p a i r . The maximum measured deformation from d i f f e r e n t i a l shrinkage between f r o n t and back o f a core was a h o r i z o n t a l s a g i t t a w i t h an asymp- t o t i c value o f 2.0 mm: v e r t i c a l displacements and angular t w i s t s d i d n o t exceed 0.5 mm and 1 mrad, r e s p e c t i v e l y . The average p o s i t i o n o f t h e median plane was s t a b l e w i t h i n 0.2 mrad.

Fig. 3

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Magnetic measurements have shown t h a t the longitudinal fluctuations of the f i e l d i n the magnet gap, due t o the spacing of the laminations a r e undetectable within the useful aperture. The only e f f e c t i s an increase by about 1.0 mm of the e f f e c t i v e gap height, due t o the f a c t t h a t the flux l i n e s enter the laminations beyond the pole edges.

In order t o inform c i v i l engineering firms about the new coremaking technique, three demonstrations of the manufacture of a steel-concrete core were organized a t CERN in the course of t h e c a l l f o r tenders. As a r e s u l t , favourable and well documented ten- ders were received and two contracts were placed, each one f o r the manufacture of 1685 cores, including production prototypes and spares. A t the same time, a contract was also placed f o r the supply of the required 3'600'000 laminations, which a r e t o be punched out of 11 '000 tons of decarburized steel sheet.

Controlled mixing of the steel sheets in the cores i s necessary in order t o reduce the spread in average coercivity. For t h i s purpose, coercivity measurements will be performed a t the steel factory, d i r e c t l y a t the end of the production l i n e , on a few sheet in a thousand, so t h a t each delivery pal l e t may be labelled with i t s average coercivity. The coercimeter, which has been especially designed and b u i l t f o r these non-destructive t e s t s , i s presented in a contributed paper [61 t o t h i s conference.

The steel-concrete cores will be delivered t o CERN a t the average r a t e of 120 per month. In addition t o geometrical and mechanical checks, enough measurements will

have t o be performed on each core t o determine i t s average magnetic f i e l d and gradi- e n t with respect to t h e others and t o define the position of i t s magnetic median plane with respect t o the reference points which will be used f o r i t s alignment i n the machine. In order t o reduce manpower and investments, i t was decided t o perform c l a s s i c a l f i e l d measurements, f o r which the core has t o be positioned in f r o n t of a measuring bench and equipped w i t h a provisional s e t of excitation bars, only on one core out of ten. The r e s u l t s of these measurements will be used t o check the conver- sion of those obtained by means of a f a s t e r measuring gear. The l a t t e r i s a s e t of inductive probes, c a l l e d "proximity detectors", which can be moved along the gap of a core on a carriage and determine the "magnetic geometry" of the gap by detecting the variations of magnetic reluctance. I t s references a r e a l a s e r beam and electronic level gauges. Another carriage magnetizes the core, so t h a t i t s remanent f i e l d may be measured by a long c o i l . W i t h t h i s equipment, which i s described in a contributed paper [71 t o t h i s conference, two teams of two technicians can measure s i x cores per day, t h u s coping w i t h the expected del ivery rate.

CI-238 JOURNAL DE PHYSIQUE

I V

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The cores o f t h e quadrupoles and sextupole a r e o f c l a s s i c a l construction, each p o l e being a c l o s e l y packed stack o f 1.5 mm l a m i n a t i o n s terminated by t h i c k e r end p l a t e s and welded t o a s t e e l p r o f i l e . For t h e c o i l s , t h e use o f anodized aluminium s t r i p i n - stead o f t h e c l a s s i c a l hollow conductor has been t r i e d out, i n order t o s i m p l i f y t h e c o i l winding process and t o increase t h e f i l l in g f a c t o r . Thanks t o t h e good thermal transmission across t h e t h i n oxide l a y e r s , adequate c o o l i n g i s provided by water- cooled heat sinks, wound around the two o r t h r e e sections i n t o which t h e c o i l can be s p l i t (Fig. 4). The o v e r a l l i n s u l a t i o n t o ground remains o f t h e c l a s s i c a l type, w i t h g l a s s - f i b r e tape impregnated under vacuum by epoxy resin. E i g h t f u l l s c a l e model c o i l s were wound w i t h t h i s technique and e x t e n s i v e l y t e s t e d w i t h c y c l i c e x c i t a t i o n w i t h o u t any d e t e r i o r a t i o n . This c o n s t r u c t i o n technique, which was described a t t h e Karl sruhe Conference on Magnet Techno1 ogy [81, i s p a r t i c u l a r l y advantageous f o r t h e quadrupoles i n t h e d i s p e r s i o n suppressor and a c c e l e r a t i o n sections, which have r e l a - t i v e l y l o w e x c i t a t i o n c u r r e n t s and a l a r g e number o f power supplies, because they are powered i n i n d i v i d u a l p a i r s .

A1 l quadrupoles and sextu- poles have t o be measured m a g n e t i c a l l y i n order t o de- termine n o t o n l y t h e p o s i t i o n o f t h e i r magnetic axes and

median planes, b u t a1 so t h e 20 hrns 150x90

harmonic components o f t h e magnetic f i e l d , on which t o - lerances a r e s e t by beam dy- namics. The measurements w i l l be performed according t o the harmonic c o i l method, by means o f a h i g h l y automated measuring system, which i s described i n a c o n t r i b u t e d paper C91 t o t h i s c o n f e r - ence. Fast and accurate alignment o f a magnetic l e n s on t h e measuring bench i s ob- t a i n e d by means o f e l e c t r o -

t r o n i c l e v e l gauges and o f a Fig. 4

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The microprocessor c o n t r o l l e d system w i l l then ramp and s e t t h e e x c i t a t i o n c u r r e n t , perform t h e measurement, analyse t h e data and o u t p u t d i r e c t l y t h e p o s i t i o n informa- t i o n and the harmonic a n a l y s i s o f t h e f i e l d . It i s expected t o reach t h e measuring r a t e o f two lenses p e r working day p e r bench.

The c o r r e c t i n g d i p o l e s have a s i m p l i f i e d c o n s t r u c t i o n , which i s more economical than t h e usual s t r u c t u r e w i t h c o i l s on t h e poles and b e t t e r compatible w i t h t h e space r e - quirements o f t h e vacuum system [lo]. The cores a r e U-shaped and can be s p l i t t o mount t h e c o i l s on the r e t u r n yoke. S i l i c o n s t e e l l a m i n a t i o n s are necessary i n these cores, t o reduce h y s t e r e s i s e f f e c t s t o t o l e r a b l e 1 eve1 s.

V

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The superconducting quadrupoles f o r t h e low-beta i n s e r t i o n s must p r o v i d e a g r a d i e n t o f 36 Tm-1 over an e f f e c t i v e l e n g t h o f 2 m. I n a d d i t i o n t o t h e usual magnetic, c r y o - genic and s t r u c t u r a l requirements, they have t o meet a number o f requirements a r i s i n g from t h e i r i n t e g r a t i o n i n t o t h e experimental apparatus. They must be i r o n - f r e e , i n o r d e r t o a l l o w t h e l i n e a r s u p e r p o s i t i o n o f t h e i r magnetic f i e l d s t o those o f t h e de- t e c t o r magnets, must r e c e i v e a bakeable vacuum chamber w i t h an i n n e r diameter o f 120 mm, must have as small as p o s s i b l e o u t e r dimensions and must be so supported and connected t o t h e i r cryogenic and e l e c t r i c a l s u p p l i e s as t o enable t h e a x i a l r e t r a c - t i o n o f t h e end cap o f t h e experimental magnet by about 2 m [Ill.

I n view o f t h e s a t i s f a c t o r y experience acquired w i t h t h e low-beta i n s e r t i o n i n t h e ISR, a compact winding s t r u c t u r e , c o n s i s t i n g o f two o r t h r e e sectors, and a monolith- i c mu1 t i f i l amentary superconductor, w i t h 50 pm diameter filaments, have been adopt- ed. This i s acceptable i n view o f t h e slow r a t e o f r i s e o f t h e f i e l d d u r i n g beam ac- c e l e r a t i o n i n LEP, which takes about 2 minutes from 20 GeV t o 50 GeV. I t s advantages a r e t h e good sharing o f stresses w i t h very l i t t l e deformation and t h e f a s t transverse propagation o f a quench, which enables t h e magnet t o d i s s i p a t e i t s s t o r e d energy w i t h o u t l o c a l overheating o r d e t e r i o r a t i o n o f t h e performance. The f o u r c o i l s , w i t h t h e i r s t a i n l e s s s t e e l cores and copper spacers, form a t h i c k - w a l l e d c y l i n d r i c a l s t r u c t u r e , which i s i n t e r n a l l y s e l f - s u p p o r t i n g and i s maintained under compression by a s e t o f s h r i n k - f i t t e d aluminium r i n g s : between t h e c o i l s and the r i n g s , t h e r e are s t a i n l e s s s t e e l spacers i n the form o f 90" sectors.

V I

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I n s t a l l a t i o n o f t h e magnets i n t o the LEP tunnel w i l l s t a r t i n the second h a l f o f 1986, when t h e f i r s t o c t a n t w i l l have been f i n i s h e d and equipped w i t h t h e machine s e r v i c e s ( t r a n s p o r t monorail, c o o l i n g pipes, e l e c t r i c a l cables, etc.). Production and t e s t i n g , however; w i l l have t o s t a r t much e a r l i e r i n order t o a l l o w f o r t h e l o w e s t p o s s i b l e manpower requirements and t h e most economical production schedules. For the d i p o l e cores and bars, t h e l a t t i c e lenses and t h e c o r r e c t o r s , which are t o be manu- f a c t u r e d i n l a r g e series, c o n t r a c t s have already been signed o r w i l l be signed w i t h i n t h i s year, p r o d u c t i o n prototypes w i l l be made and t e s t e d i n 1984 and r e g u l a r produc- t i o n w i l l extend over about t h r e e years, ending l a t e i n 1987 o r e a r l y i n 1988. The magnets near t h e i n t e r a c t i o n p o i n t s , which are l e s s numerous, can be produced w i t h j u s t a modest advance w i t h r e s p e c t t o i n s t a l l a t i o n , from mid-1986 t o mid-1988.

D i p o l e e x c i t a t i o n bars and vacuum chambers w i l l be mounted onto p a i r s o f cores, which have been p r e v i o u s l y a l i g n e d w i t h r e s p e c t t o each other, i n a h a l l adjacent t o a de- d i c a t e d access shaft. The s t r a i g h t - s e c t i o n groups, c o n s i s t i n g o f a quadrupole, a sex- t u p o l e and, i n most cases, a c o r r e c t o r on a common g i r d e r , w i t h t h e i r vacuum chamber and beam monitor, w i l l a l s o be b u i l t up i n t h a t h a l l . A l l these assemblies w i l l e n t e r t h e tunnel v i a t h e s h a f t and w i l l be d r i v e n t o t h e i r f i n a l l o c a t i o n by means o f a monorail system, w i t h ad-hoc boogies and r i g i d girders. I n s t a l l a t i o n w i l l be perform- ed by two teams i n para1 l e l , one proceeding clockwise, t h e o t h e r anticlockwise.

I n each octant, a l l s t r a i g h t - s e c t i o n assemblies w i l l be i n s t a l l e d f i r s t , because t h e quadrupoles have t o be used as monuments f o r the p r e c i s i o n survey. The d i p o l e s w i l l then be t r a n s p o r t e d and i n s t a l l e d a t t h e average r a t e o f t h r e e p a i r s per day per team. Hydraulic, e l e c t r i c a l and vacuum i n t e r c o n n e c t i o n s w i l l then be made e i t h e r by welding o r by b o l t i n g and a l l necessary t e s t s w i l l be c a r r i e d o u t i n sequence. It i s expected t h a t t h e l a s t d i p o l e may be i n s t a l l e d b e f o r e t h e end o f 1988.

REFERENCES

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