POSSIBILITIES OF POLARIZED PROTONS IN SppS AND OTHER HIGH ENERGY HADRON COLLIDERS

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POSSIBILITIES OF POLARIZED PROTONS IN SppS AND OTHER HIGH ENERGY HADRON COLLIDERS

E. Courant

To cite this version:

E. Courant. POSSIBILITIES OF POLARIZED PROTONS IN SppS AND OTHER HIGH EN- ERGY HADRON COLLIDERS. Journal de Physique Colloques, 1985, 46 (C2), pp.C2-713-C2-715.

�10.1051/jphyscol:1985291�. �jpa-00224610�

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JOURNAL DE PHYSIQUE

Colloque C2, supplément au n°2, Tome *6, février 1985 page C2-713

POSSIBILITIES OF POLARIZED PROTONS IN SppS AND OTHER HIGH ENERGY HADRON COLLIDERS*

E.D. Courant

Brookhaven National Laboratory, Upton NY 11975, U.S.A.

and

State University of Sew York, Stony Brook, WY 11794, U.S.A.

Résumé . Nous examinons dans cette contribution quelques possibilités pour travail- ler avec des protons polarisés dans le collisionneur du SPS et dans d'autres collisionneurs à hadrons à haute énergie et nous concluons que c'est faisable.

Abstract. The purpose of this contribution is to examine some possibilities for operating polarized protons in the SppS collider and in other high energy hadron colliders and we conclude that it is feasible.

The announced subject of this panel discussion is "Polarized Protons in the SppS", but I would like to extend the terms of reference to include hadron colliders above 200 GeV in general. There are more than half a dozen machines in existence, being built, or being contemplated in this category, and polarized beams might be of interest in all of them:

Injector NAME Energy (GeV) Energies SppS (CERN) pp 270-350 0.8, 14-30 Tevatron (FNAL) pp 800-1000 10, 150 RHIC (BNL) p-ion 250-350 20-30 HERA (DESY) e-p 850 40 UNK (Serpukhov) p-p 3000 70 LHC (CERN) p-p 5000-8000 0.8, 14-30, 350 SSC (USA) p-p 20000 70, 1000

To get collisions with polarized protons in these machines, one requires the following:

1. A source of polarized protons with respectable intensity.

2. Acceleration in the preinjector(s) without depolarization.

3. Traversal of polarization resonances in booster synchrotrons (up to 15-70 GeV).

4. Elimination of resonances in the large rings (above 100 GeV).

1. To obtain interesting luminosities, the injector ring should have around 1012

polarized protons. This implies and improvement in the performance capability of polarized sources of a factor around 100 compared to present-day achievements.

Work supported by U.S. Department of Energy

Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:1985291

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C2-714 JOURNAL DE

PHYSIQUE

I

am t o l d t h a t t h i s a p p e a r s t o be a very r e a s o n a b l e hope.

2.

It i s

known t h a t l i n e a r a c c e l e r a t o r s i n t h e multi-100 MeV range do n o t d e p o l a r i z e a p p r e c i a b l y .

3. T r a v e r s a l of resonances h a s been demonstrated a t Argonne, S a c l a y , and Brookhaven up t o e n e r g i e s of 15-20 GeV. Extending t h e s e t e c h n i q u e s should be s t r a i g h t f o r w a r d up t o 30 GeV o r t h e r e a b o u t s .

4.

Above 30 GeV t h e " S i b e r i a n Snake" t e c h n i q u e s should be f e a s i b l e .

A 1983 s t u d y by Bovet, Moehl, and Ruth i n d i c a t e s t h a t p o l a r i z e d p r o t o n opera- t i o n should be f e a s i b l e f o r t h e SppS

To

see

what t h e problems may be f o r t h a t and o t h e r c o l l i d e r s , l e t u s b r i e f l y r e c a l l t h e f a c t s of d e p o l a r i z i n g resonances and " S i b e r i a n snakes" a s o u t l i n e d by R. Ruth a t t h i s Symposium.

D e p o l a r i z i n g r e s o n a n c e s occur when t h e s p i n p r e c e s s i o n frequency e q u a l s a f r e q - uency c o n t a i n e d i n t h e spectrum of t h e f i e l d s e e n by t h e beam. These f r e q u e n c i e s ( i n u n i t s of t h e r e v o l u t i o n f r e q u e n c y ) a r e :

k ( a n y i n t e g e r ) due t o o r b i t i m p e r f e c t i o n s ;

kP ^fv (where f

i s

t h e v e r t i c a l b e t a t r o n t u n e ) f o r " i n t r i n s i c resonances"; h e r e P

i s

t h e p e r i o d i c i t y of t h e l a t t i c e .

The s p i n p r e c e s s i o n frequency, i n a r i n g where t h e i d e a l o r b i t l i e s i n

a

p l a n e ,

i s

normally

YG = E/0.56 G e V

where G 5 (g-2)/2= 1.793

i s

t h e anomalous moment f a c t o r of t h e proton. Therefore Smperfection r e s o n a n c e s a r i s e e v e r y 560 MeV; i n t r i n s i c r e s o n a n c e s i n a machine w i t h 4 s u p e r p e r i o d s such a s t h e SppS a r i s e twice e v e r y 4x0.56 GeV, o r on t h e average every 1.12 GeV. T h e r e f o r e t h e r e a r e hundreds of r e s o n a n c e s i n a machine of t h e e n e r g y r a n g e of t h e SppS, and thousands i n TeV machines.

The t r a d i t i o n a l c u r e , used a t t h e ZGS, S a t u r n e and t h e AGS,

is:

F i g h t them a l l ! This

i s

p o s s i b l e f o r e n e r g i e s of t e n s of GeV, where t h e r e a r e "only" around 1 0 t o 100 resonances, some of them q u i t e weak. But f o r h i g h e r e n e r g i e s this

is

q u i t e h o p e l e s s , both because t h e r e a r e v e r y many r e s o n a n c e s and because t h e r e s o n a n c e s tend t o be s t r o n g e r a s t h e energy goes up (due t o a f a c t o r E i n t h e p r e c e s s i o n equa- t i o n s ) .

The

c u r e

i s

t h e famous " S i b e r i a n Snake". T h i s

i s

a d e v i c e which makes

t h e

s p i n p r e c e s s i o n f r e q u e n c y e s s e n t i a l l y c o n s t a n t , independent o f energy. T h i s

is

accom- p l i s h e d by s p i n r o t a t o r s , which p r e c e s s t h e s p i n by 180 Oabout e i t h e r t h e l o n g i t u d - i n a l ("Type

I

snake") o r t h e t r a n s v e r s e h o r i z o n t a l (Type I1 snake) a x i s .

The r o t a t o r s o r "snakes" e a c h c o n s i s t of a s e t of 6 t o 10 i n d i v i d u a l d i p o l e o r h e l i x magnets which d e f l e c t t h e beam h o r i z o n t a l l y o r v e r t i c a l l y , and a t t h e same time r o t a t e t h e s p i n about t h e v e r t i c a l o r h o r i z o n t a l a x i s . The magnets of e a c h snake a r e a r r a n g e d s o t h a t t h e y r o t a t e t h e s p i n by 180° w h i l e a t t h e same time g i v i n g no n e t d e f l e c t i o n o r displacement t o t h e beam. Numerous d e t a i l e d c o n f i g u r - a t i o n s f o r s n a k e s of t y p e

I

o r type I1 have been devised. They

a l l

d e f l e c t t h e o r b i t a l o n g a t w i s t e d p a t h (hence t h e name "snake"); w i t h f i e l d of 2 t o 4 T e s l a t h e maximum e x c u r s i o n

i s

around 5 t o 1 5 an (depending on t h e d e t a i l e d c o n f i g u r a t i o n ) f o r

20 G e V p r o t o n s , and

is

i n v e r s e l y p r o p o r t i o n a l t o energy. A snake needs a t o t a l of 15 t o 25 T e s l a - m e t e r s of magnets; t h e r e f o r e t h e f r e e space needed i n t h e l a t t i c e t o accommodate

a

snake

is

around 20

m

i f i r o n magnets a r e used, and 10

m

i n t h e c a s e of s u p e r c o n d u c t i n g magnets. The magnets need enough a p e r t u r e t o accommodate t h e snak- i n g o r b i t

a t

i n j e c t i o n energy; i f t h e i n j e c t i o n e n e r g y

i s

very high, s m a l l - a p e r t u r e

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magnets w i l l do ( a s i n t h e c a s e of t h e SSC).

With one snake of Type I o r I1 p r e s e n t , t h e s p i n p r e c e s s i o n frequency i s j u s t 1/2, i.e. t h e s p i n p r e c e s s e s around t h e e q u i l i b r i u m s p i n d i r e c t i o n by j u s t 180"

p e r r e v o l u t i o n . Thus t h e s p i n p r e c e s s i o n frequency i s j u s t a s f a r a s p o s s i b l e from resonance with i m p e r f e c t i o n s ( i n t e g r a l v a l u e ) , and

i s

a l s o removed from resonance w i t h b e t a t r o n o s c i l l a t i o n s provided t h e b e t a t r o n tune i s not h a l f i n t e g r a l . With g i v e n snake magnets t h e s p i n r o t a t i o n i s independent of energy while the o r b i t e x c u r s i o n is i n v e r s e l y p r o p o r t i o n a l t o energy.

The e x c u r s i o n i s small enough t o f i t i n t o a reasonable magnet a p e r t u r e

15 an,

s a y ) f o r e n e r g i e s above 20 t o 30

GeV. On

t h e o t h e r hand, t h e "resonance f i g h t i n g " mode works up t o about t h i s range.

In

t h e c a s e of i n j e c t o r r i n g s i n t h e 40-100

GeV r a n g e it

may be d e s i r a b l e , i f p o s s i b l e , t o s w i t c h from t h e "resonance f i g h t i n g " mode t o t h e S i b e r i a n snake mode i n t h e same r i n g - t h i s w i l l have t o be e x p l o r e d i n f u t u r e c a l c u l a t i o n s .

At 180" from t h e snake t h e e q u i l i b r i u m s p i n d i r e c t i o n i s independent of energy, and

i s

p a r a l l e l t o t h e s n a k e ' s r o t a t i o n a x i s . Elsewhere i n t h e a r c s t h e s p i n r o t a t e s r a p i d l y i n t h e h o r i z o n t a l plane, and i t s o r i e n t a t i o n a t any point v a r i e s w i t h energy.

I f one snake i s good, two must be b e t t e r . If

we

have one snake of type I and one of type 11, 180" a p a r t , t h e p r e c e s s i o n frequency i s s t i l l 112, but t h e

e q u i l i b r i u m s p i n i s now up i n one 180' a r c and down i n t h e o t h e r , independent o f energy. T h i s i s e v i d e n t l y a more s t a b l e s t a t e of a f f a i r s .

However, t h e b e h a v i o r of t h e i d e a l machine w i l l

be

a f f e c t e d by t h e presence of e r r o r s .

A t

h i g h energy t h e r e w i l l be many complete p r e c e s s i o n s i n each a r c , c o u n t e r b a l a n c e d by an e q u a l number i n t h e o p p o s i t e d i r e c t i o n i n t h e o t h e r a r c . I f , i n s t e a d of a s i n g l e p a i r of snakes, we have more, t h e a r c s

w i l l

be s h o r t e r and t h e number of p r e c e s s i o n s per a r c w i l l be fewer. I f , somewhat a r b i t r a r i l y ,

we

wish t o have n o t more t h a n about 200 t o 500 p r e c e s s i o n s per a r c , t h e a r c s should have no more than 2000 t o 5000 T-m of bending magnets, i.e. t h e r e should be a "snake" e v e r y k i l o m e t e r o r two a l o n g t h e r i n g circumference. Thus SpFS can probably manage w i t h one p a i r of s n a k e s ;

HERA

o r t h e Tevatron may be b e t t e r o f f w i t h 4 o r 6 s n a k e s , w h i l e t h e SSC (about 100

km

c i r c u m f e r e n c e ) may want 20 t o 50 snakes.

Much of t h e p h y s i c s i n t e r e s t i n p o l a r i z e d beams p e r t a i n s t o h e l i c i t y , i.e.

l o n g i t u d i n a l p o l a r i z a t i o n . I n t h e multi-snake l a t t i c e s d e s c r i b e d h e r e t h e p o l a r i z a t i o n i s always v e r t i c a l ( t r a n s v e r s e ) except i n t h e middle of t h e snakes.

Therefore f u r t h e r s p i n r o t a t o r s may be d e s i r a b l e t o t u r n t h e s p i n i n t o t h e l o n g i t u d i n a l d i r e c t i o n a t some of t h e beam c r o s s i n g p o i n t s . This can be accomplished by s p l i t t i n g some of t h e snakes i n t o two 90' r o t a t o r s , o r e l s e by i n c o r p o r a t i n g d e d i c a t e d 90" r o t a t o r s i n a d d i t i o n t o t h e snakes.

I n c o n c l u s i o n ,

i t