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Design and performance of a small-angle, high-intensity secondary particle beam from the CERN proton synchrotron
NUCLEAR
INSTRUMENTS
AND
METHODS
20
(1963) 66-70,
NORTH-HOLLAND
PUBLISHING
D E S I G N A N D P E R F O R M A N C E OF A S M A L L - A N G L E , H I G H - I N T E N S I T Y
CO
SECONDARY
PARTICLE BEAM FROM THE CERN PROTON SYNCHROTRON M BARB1ER, J
D DO\VELL*, P I P KALMUS**, 13 LEONTIC, A LUNDBY, R I~IEUNIER, G I)ETRUCCI, L SOLINAS, J
P STROOT and 1~ SZEPTYCKA C E R N , Geneva
Presented by J
The production of high-intensity beams from the C E R N Proton Synchrotron using standard beam transport equipment is limited by the closeness to the PS ring at whmh quadrupoles can be placed For relatively low-momentum particles ( < 4 GeV/c) a beam of near optimum intensity had been achmved I), with existing beam transport at a production angle of 14 ° The first quadrupole in this beam was placed at about 5 metres from the
D Dowell
PS internal target giving a solid angle acceptance of 5 × 10 4 sterad Since the yield of particles increases with decreasing production angle, it seemed desirable to consider specialized beam transport arrangements which could be used at small angles without serious reduction in collection solid angle In order to achieve the flexibility demanded by the expenments planned m the beam 1) it should
Fig 1 General layout of beam 1) j D Dowell, VV Koch, B Leontlc, A Lundby, R Meumer, J P Stroot, and M Szeptycka, Phystcs Letters 1 (1962) 53
*) On leave from Physms Department, University of Birmingham **) Member of Argonne National Laboratory vlsmng team at CE1RN 66
A SMALL-ANGLE,
HIGH
IN'TENSITY
conform to t h e following r e q u i r e m e n t s 1) t h e m o m e n t u m should be c o n t i n u o u s l y variable from 0.5 to 3 GeV/c for particles of either sign, n) the effect of the PS f r m g m g field should be small so t h a t t h e optical properties of the b e a m would, as Momentum
PARTICLE
BEAM
67
M2, which b e n d the particles 25 ° a n d focus t h e m into a m o m e n t u m - d i s p e r s e d image 8 m a w a y from t h e t a r g e t A t this p o i n t a m o m e n t u m s h t S is placed, followed b y a space in which counters can be inserted for differentiating between t h e mesons
sttt
.
2~7
"
Fig
SECONDARY
M1
170
2 Detailed l a y o u t of the two special m a g n e t s (all dlmensmns are m mllhmetres)
m u c h as possible, be i n d e p e n d e n t of sign a n d mom e n t u m of the particles, in) the presence of magnetic a p p a r a t u s close to the PS should not p e r t u r b the circulating p r o t o n orbit
OI r-!
F i g 3 Cross-sectional view of the entrance of the first special m a g n e t The cross-sectmnal area of the v a c u u m pipe mcreases w i t h the distance from the t a r g e t The accepted beam size (1 8 cm dmmeter) is represented by the shaded circle
The solution a d o p t e d is shown in figs 1--3 The b e a m consists of two parts, the first comprising two special focusing a n d b e n d i n g magnets, M 1 a n d
a n d nucleons The second p a r t of the b e a m consists of s t a n d a r d C E R N b e a m t r a n s p o r t elements The m a g n e t s M3 (1 m) a n d 314 (2 m) b e n d the b e a m into the e x p e r i m e n t a l area, a n d t o g e t h e r with t h e triplet Q1, Q2 a n d Q3 (all 1 m long a n d 20 cm diameter quadrupoles) they produce an a c h r o m a t i c image at the position of the liquid hydrogen t a r g e t 1) The m a g n e t M1 is placed in c o n t a c t with the v a c u u m c h a m b e r in a 3 m long straight section of PS (figs 2 a n d 3) The m e d i a n plane field approaches zero towards the v a c u u m c h a m b e r A t this position there is a n e u t r a l pole which shields the circulating b e a m in the PS from the influence of the strong focusing m a g n e t The m i n i m u m angle a n d the m a x i m u m m o m e n t u m of the secondary b e a m which can be accepted a n d t r a n s p o r t e d a w a y from the PS r i g b y such a m a g n e t are d e t e r m i n e d b y a n u m b e r of practical considerations such as i) the m i n i m u m dimensions of the v a c u u m c h a m b e r in the s t r a i g h t section of PS which can be tolerated w i t h o u t losing accelerated protons to t h e walls, u) the m a x i m u m radial position at which a n Internal t a r g e t can be placed a n d on to which t h e circulating protons can still be steered efficiently, iii) the m a x i m u m field s t r e n g t h in the deflection III
BLAM TRANSPORT
68
et al
M BARBIER
m a g n e t , iv) the m i n i m u m thickness of the neutral pole of the deflection m a g n e t compatible with the r e q u i r e m e n t of a s t r a y field on the accelerated proton b e a m of less t h a n 5 gauss × m verhcally and 1 gauss × m horizontally
in order to provide a small image at low m o m e n t u m for a n u m b e r of o t h e r e x p e r i m e n t s now planned in the b e a m The v a c u u m c h a m b e r cuts down the solid angle acceptance b y an e s t i m a t e d factor of two W i t h o u t the c h a m b e r in the first two special
TABLE 1 Beam t r a n s p o r t p a r a m e t e r s Maximum momentum 3 GeVlc Solid angle acceptance (without v a c u u m pipe) 3 × 10 -4 steradian
M o m e n t u m bite zlp/p M a g m f l c a t l o n a t 1st focus M a g m h c a t m n a t 2nd focus
:t: 2 5 % 1 6 horizontal, 2 5 v e r t m a l 2 horizontal, 4 0 v e r t m a l
Functmn
Physical l e n g t h (em)
Gradmnt at 1 GeV/c (gauss]cm)
Mean o r b i t field a t GeV/c (gauss)
1st special magnet M1 B e n d i n g r a d m s 890 cm* B e n d i n g angle 9 9 °
HDF HDF Bending HDF HF
35 35 30 10 60
810 468 0 468 408
3750 3750 3750 3750 3750
2nd specml magnet M2
HF Bending HDF Bending
66 15 95 40
262 5 0 262 5 0
3950 3950 3950 3950
0
5700
Magnet
B e n d i n g radius 846 cm B e n d i n g angle 15 l °
M3
B e n d i n g 10 °
100
Q1
HF
100
143
--
Q2
HDF
lOO
220
--
Q3
HF
100
143
--
M4
B e n d i n g 20 °
200
0
6000
*) This r a d m s refers t o the last 100 cm, the first 70 cm are n o t curved IZF H o r i z o n t a l l y focusing
H D F H o r i z o n t a l l y defocusmg
The g e o m e t r y chosen is conservative on all these points and exerts no unusual strain on the operation of the PS Since the PS m a g n e t preceding our b e a m (no 5 in fig 2) is horizontally defocusmg, the proton b e a m thus has relatively small horizontal size as it enters the section The PS v a c u u m c h a m b e r could therefore be somewhat reduced to the cross-section in fig 3 The internal target is placed in Its normal central position with the possibility of displacing it 3 cm radially outwards or inwards A 0 2 m m thick m y l a r window closes the exit port of the beam and a similar m y l a r window covers the entrance to the vacuum chamb e r in M 1 W h e n the b e a m was originally conceived for the e x p e r i m e n t s in ref 1) there was no need for the v a c u u m c h a m b e r in M1 I t was later introduced
m a g n e t s the solid angle acceptance is about 3 × 10 -4 sterad The m a g n e t M1 is designed with a straight horizontally defocuslng section followed b y a curved horizontally focusing section The bending power in the first section is arranged to move the orbit of the secondary b e a m to the central position in the subsequent section in such a way t h a t it thereafter follows a p a t h whose radius is t h a t of the magnet (see fig 2) The focusing strength is arranged so t h a t the emergent b e a m is approximately parallel in b o t h planes The deflection in M1 is 10 ° and is such t h a t the b e a m passes the beginning of the n e x t PS m a g n e t section at 50 cm from the proton orbit where the fringing field is negligible The first m a g n e t M1 is followed after 1 5 metres
A SMALL-ANGLE,
HTGIt-INTENSITY
of free space b y a n o t h e r strong focusing b e n d i n g m a g n e t M2 of larger size (4 cm g a p a n d 12 cm acceptance horizontally) M2 b e n d s the b e a m 15 ° a n d refocuses it in b o t h planes a t a point a b o u t 8 m e t r e s from t h e PS t a r g e t w i t h a magnification of 1.6 h o r i z o n t a l l y a n d 2 5 vertically B o t h m a g n e t s M1 a n d M2 are fitted with a d d i t i o n a l coils in u n i f o r m field sections so t h a t the b e n d i n g can be v a r i e d by a few p e r cent while the focusing is kept c o n s t a n t A more detailed report on these m a g n e t s will be p u b l i s h e d elsewhere 2) A t the first focus t h e m o m e n t u m dispersion is 1 6 cm a n d 4 6 m r a d for a 1 % change in m o m e n tum* A n a d j u s t a b l e m o m e n t u m slit is placed at the first focus (S in fig i) I t is followed b y a 1-metre b e n d i n g m a g n e t M3 giving 10 ° deflection, three 1m e t r e q u a d r u p o l e s Q1, Q2, Q3 a n d a 2-metre b e n d -
SECONDARY
PARTICLE
BEAM
69
planes a n d gives a good m o m e n t u m transmission A n image with v e r y good c h r o m a t i c correction has been o b t a i n e d a t 22 m from the PS t a r g e t Act u a l l y t h e b e a m size at this position, m e a s u r e d directly w i t h a Polaroid 3000 speed film a n d also with scintillation counters, appears to be a b o u t 1 to 2 cm 2 w h e n using a 1 cm a p e r t u r e m o m e n t u m s h t a n d increases b y only a factor 2 in area w h e n the m o m e n t u m slit IS opened to 10 cm This Increase is purely due to c h r o m a t i c a b e r r a t i o n s a n d agrees well w i t h t h e calculation The b e a m optics are shown schematically in fig 4 D u r i n g the design stage b e a m optics calculations were carried out with b o t h a n analogue a n d a digital c o m p u t e r usmg a p r o g r a m m e called T R A M P s) Quadrupole a p p r o x i m a t i o n s were used for t h e sections of the strong focusing b e n d i n g m a g n e t s The calculations were checked with
22m
II "]
k'IOhIENTUMsLIT
I
.
FOOUN CP5 TARGET
,5 2
I'1f
Q¢
02
Q..~
/"/2
~ .
S! Fig
4 S c h e m a t i c r e p r e s e n t a t i o n of t h e b e a m envelope m t h e horizontal plane T h e d a s h e d hne indicates t h e t r a l e c t o r y of a particle of h i g h e r m o m e n t u m which s t a r t e d a l o n g t h e m e a n a x i s of t h e b e a m
lng m a g n e t M4 These c o m p o n e n t s are all s t a n d a r d C E R N u n i t s The q u a d r u p o l e s can be used as a s y m m e t r i c a l triplet to provide a d o u b l y focused image at a c o n v e n i e n t p o m t b e y o n d the final b e n d i n g m a g n e t The final b e n d i n g angle (20 ° ) h a s been chosen so as to give a n a c h r o m a t i c image at the required distance along the b e a m T h e use of a triplet keeps magnifications fairly low in b o t h
floating wlre measurements, including a verification of the position of t h e first focus a n d the dispersion The t o t a l b e a m Intensities were m e a s u r e d with a n ionization c h a m b e r a n d b y s c a n n i n g across the b e a m with two r e m o t e l y m o v a b l e scintillation counters of 0 25 cm 2 area The results w i t h t h e v a c u u m c h a m b e r all along t h e b e a m are given in
* T h e t o t a l m o m e n t u m acceptance of ~ 2 5 % ]s h m l t e d b y t h e h o r i z o n t a l a c c e p t a n c e of the q u a d r u p o l e s I t could be m a d e ~ 50 o~ l a r g e r b y p l a c i n g a q u a d r u p o l e n e a r e r to the first focus, b u t a l a r g e r m o m e n t u m b a n d w a s n o t required for t h e e x p e r i m e n t s a t p r e s e n t planned
3) M Barbler, L Chareyre, G Petruccl, M S z e p t y c k a and L Sohnas, C E R N 62-24 3) j W G a r d n e r a n d D ~,Vhxteslde T R A M P T r a c k i n g and Matehmg Programme NIRL/M/21 National Institute, Hatwell, J u l y 1961 III
BEAM TRANSPORT
M BARBIER el al
70
fig 5 T h e c i r c u l a t i n g p r o t o n s were accelerated to 19 2 GeV/c a n d i n t e r a c t e d w i t h a Be t a r g e t in the s h a p e of a 1 m m wire, 20 m m long in t h e proton b e a m direction W i t h o u t the v a c u u m chamber m M1 a n d M2 t h e m t e n s l t y s h o u l d b e l a r g e r b y a b o u t a f a c t o r of t w o T h e t o t a l i n t e n s i t i e s agree w i t h d a t a f r o m this l a b o r a t o r y 4) a n d f r o m B r o o k h a v e n 5) T h e l o w e r = - i n t e n s i t y r e l a t l v e to t h a t for =+ is p a r t l y d u e to t h e effect of t h e PS f r m g m g field m
.lo-1
//
RATIO
at PS internal target
// //
10-2
K"
--p--
at 22 m T,J•**,
/////:at22m -
2406
/
//'~
\
1
B'*
2
GeV/e
3
Fig 6 Particle ratios as measured at 22 m from the target
and corrected for decay to give ratios at the target
106
~/
1
2G~,/c
3
Fig 5 Intensities observed per 1011 clrculatmg protons Protons of 192GeV/c struck a Be target Measurements were made 22 m from the target
zJp[p = ± 2 5 %
be i n c r e a s e d s o m e w h a t b y displacing t h e t a r g e t r a d i a l l y o u t w a r d s H o w e v e r , since t h e r e still r e m a i n s a n excess of pomt~ve p l o n s we w o u l d t e n t a t i v e l y i n t e r p r e t it as a difference in yield at the target Particle a b u n d a n c e s as m e a s u r e d w i t h a D I S C C h e r e n k o v c o u n t e # ) are s h o w n in fig 6
t h e v i c i n i t y of t h e t a r g e t A t 1 GeV/c t h i s p r o d u c e s a difference of 0 7 ° b e t w e e n t h e p r o d u c t i o n a n g l e s for p o s i t i v e a n d n e g a t i v e particles, r e s u l t i n g m a difference in i n t e n s i t i e s of a b o u t 10 % P r e l i m i n a r y m e a s u r e m e n t s s h o w e d t h a t t h e ~ - m t e n s l t y could
Acknowledgements
4) A Dlddens, E Llllethun, G Manning, A E Taylor, G I Walker and A Wetherell, private communication 5) R L Cool, private commumcatlon
6) R Meumer, J P Stroot, B Leontlc, A Lundby and P Dutell, Nucl Instr and Meth 17 (1962) 1
W e are i n d e b t e d to P Dutell, T A R o m a n o w s k l , N W h y t e a n d E J N W i l s o n w h o p a r t i c i p a t e d in s e t t m g u p the b e a m
DISCUSSION
Could you explam why the ywld of antxprotons is not increasing at smaller angles ~ JENTSCHKE
DOWELL I t has been reported by Droblewskx at the High Energy Conference that the average transverse too-
mentum mcreases wxth mcreasmg parhcle mass The productxon of heavier partxcles ts therefore less peaked m the forward dtrectlon As far as I know there is no theoretical explanatxon for this
INSTRUMENTS
AND
METHODS
20
(1963) 66-70,
NORTH-HOLLAND
PUBLISHING
D E S I G N A N D P E R F O R M A N C E OF A S M A L L - A N G L E , H I G H - I N T E N S I T Y
CO
SECONDARY
PARTICLE BEAM FROM THE CERN PROTON SYNCHROTRON M BARB1ER, J
D DO\VELL*, P I P KALMUS**, 13 LEONTIC, A LUNDBY, R I~IEUNIER, G I)ETRUCCI, L SOLINAS, J
P STROOT and 1~ SZEPTYCKA C E R N , Geneva
Presented by J
The production of high-intensity beams from the C E R N Proton Synchrotron using standard beam transport equipment is limited by the closeness to the PS ring at whmh quadrupoles can be placed For relatively low-momentum particles ( < 4 GeV/c) a beam of near optimum intensity had been achmved I), with existing beam transport at a production angle of 14 ° The first quadrupole in this beam was placed at about 5 metres from the
D Dowell
PS internal target giving a solid angle acceptance of 5 × 10 4 sterad Since the yield of particles increases with decreasing production angle, it seemed desirable to consider specialized beam transport arrangements which could be used at small angles without serious reduction in collection solid angle In order to achieve the flexibility demanded by the expenments planned m the beam 1) it should
Fig 1 General layout of beam 1) j D Dowell, VV Koch, B Leontlc, A Lundby, R Meumer, J P Stroot, and M Szeptycka, Phystcs Letters 1 (1962) 53
*) On leave from Physms Department, University of Birmingham **) Member of Argonne National Laboratory vlsmng team at CE1RN 66
A SMALL-ANGLE,
HIGH
IN'TENSITY
conform to t h e following r e q u i r e m e n t s 1) t h e m o m e n t u m should be c o n t i n u o u s l y variable from 0.5 to 3 GeV/c for particles of either sign, n) the effect of the PS f r m g m g field should be small so t h a t t h e optical properties of the b e a m would, as Momentum
PARTICLE
BEAM
67
M2, which b e n d the particles 25 ° a n d focus t h e m into a m o m e n t u m - d i s p e r s e d image 8 m a w a y from t h e t a r g e t A t this p o i n t a m o m e n t u m s h t S is placed, followed b y a space in which counters can be inserted for differentiating between t h e mesons
sttt
.
2~7
"
Fig
SECONDARY
M1
170
2 Detailed l a y o u t of the two special m a g n e t s (all dlmensmns are m mllhmetres)
m u c h as possible, be i n d e p e n d e n t of sign a n d mom e n t u m of the particles, in) the presence of magnetic a p p a r a t u s close to the PS should not p e r t u r b the circulating p r o t o n orbit
OI r-!
F i g 3 Cross-sectional view of the entrance of the first special m a g n e t The cross-sectmnal area of the v a c u u m pipe mcreases w i t h the distance from the t a r g e t The accepted beam size (1 8 cm dmmeter) is represented by the shaded circle
The solution a d o p t e d is shown in figs 1--3 The b e a m consists of two parts, the first comprising two special focusing a n d b e n d i n g magnets, M 1 a n d
a n d nucleons The second p a r t of the b e a m consists of s t a n d a r d C E R N b e a m t r a n s p o r t elements The m a g n e t s M3 (1 m) a n d 314 (2 m) b e n d the b e a m into the e x p e r i m e n t a l area, a n d t o g e t h e r with t h e triplet Q1, Q2 a n d Q3 (all 1 m long a n d 20 cm diameter quadrupoles) they produce an a c h r o m a t i c image at the position of the liquid hydrogen t a r g e t 1) The m a g n e t M1 is placed in c o n t a c t with the v a c u u m c h a m b e r in a 3 m long straight section of PS (figs 2 a n d 3) The m e d i a n plane field approaches zero towards the v a c u u m c h a m b e r A t this position there is a n e u t r a l pole which shields the circulating b e a m in the PS from the influence of the strong focusing m a g n e t The m i n i m u m angle a n d the m a x i m u m m o m e n t u m of the secondary b e a m which can be accepted a n d t r a n s p o r t e d a w a y from the PS r i g b y such a m a g n e t are d e t e r m i n e d b y a n u m b e r of practical considerations such as i) the m i n i m u m dimensions of the v a c u u m c h a m b e r in the s t r a i g h t section of PS which can be tolerated w i t h o u t losing accelerated protons to t h e walls, u) the m a x i m u m radial position at which a n Internal t a r g e t can be placed a n d on to which t h e circulating protons can still be steered efficiently, iii) the m a x i m u m field s t r e n g t h in the deflection III
BLAM TRANSPORT
68
et al
M BARBIER
m a g n e t , iv) the m i n i m u m thickness of the neutral pole of the deflection m a g n e t compatible with the r e q u i r e m e n t of a s t r a y field on the accelerated proton b e a m of less t h a n 5 gauss × m verhcally and 1 gauss × m horizontally
in order to provide a small image at low m o m e n t u m for a n u m b e r of o t h e r e x p e r i m e n t s now planned in the b e a m The v a c u u m c h a m b e r cuts down the solid angle acceptance b y an e s t i m a t e d factor of two W i t h o u t the c h a m b e r in the first two special
TABLE 1 Beam t r a n s p o r t p a r a m e t e r s Maximum momentum 3 GeVlc Solid angle acceptance (without v a c u u m pipe) 3 × 10 -4 steradian
M o m e n t u m bite zlp/p M a g m f l c a t l o n a t 1st focus M a g m h c a t m n a t 2nd focus
:t: 2 5 % 1 6 horizontal, 2 5 v e r t m a l 2 horizontal, 4 0 v e r t m a l
Functmn
Physical l e n g t h (em)
Gradmnt at 1 GeV/c (gauss]cm)
Mean o r b i t field a t GeV/c (gauss)
1st special magnet M1 B e n d i n g r a d m s 890 cm* B e n d i n g angle 9 9 °
HDF HDF Bending HDF HF
35 35 30 10 60
810 468 0 468 408
3750 3750 3750 3750 3750
2nd specml magnet M2
HF Bending HDF Bending
66 15 95 40
262 5 0 262 5 0
3950 3950 3950 3950
0
5700
Magnet
B e n d i n g radius 846 cm B e n d i n g angle 15 l °
M3
B e n d i n g 10 °
100
Q1
HF
100
143
--
Q2
HDF
lOO
220
--
Q3
HF
100
143
--
M4
B e n d i n g 20 °
200
0
6000
*) This r a d m s refers t o the last 100 cm, the first 70 cm are n o t curved IZF H o r i z o n t a l l y focusing
H D F H o r i z o n t a l l y defocusmg
The g e o m e t r y chosen is conservative on all these points and exerts no unusual strain on the operation of the PS Since the PS m a g n e t preceding our b e a m (no 5 in fig 2) is horizontally defocusmg, the proton b e a m thus has relatively small horizontal size as it enters the section The PS v a c u u m c h a m b e r could therefore be somewhat reduced to the cross-section in fig 3 The internal target is placed in Its normal central position with the possibility of displacing it 3 cm radially outwards or inwards A 0 2 m m thick m y l a r window closes the exit port of the beam and a similar m y l a r window covers the entrance to the vacuum chamb e r in M 1 W h e n the b e a m was originally conceived for the e x p e r i m e n t s in ref 1) there was no need for the v a c u u m c h a m b e r in M1 I t was later introduced
m a g n e t s the solid angle acceptance is about 3 × 10 -4 sterad The m a g n e t M1 is designed with a straight horizontally defocuslng section followed b y a curved horizontally focusing section The bending power in the first section is arranged to move the orbit of the secondary b e a m to the central position in the subsequent section in such a way t h a t it thereafter follows a p a t h whose radius is t h a t of the magnet (see fig 2) The focusing strength is arranged so t h a t the emergent b e a m is approximately parallel in b o t h planes The deflection in M1 is 10 ° and is such t h a t the b e a m passes the beginning of the n e x t PS m a g n e t section at 50 cm from the proton orbit where the fringing field is negligible The first m a g n e t M1 is followed after 1 5 metres
A SMALL-ANGLE,
HTGIt-INTENSITY
of free space b y a n o t h e r strong focusing b e n d i n g m a g n e t M2 of larger size (4 cm g a p a n d 12 cm acceptance horizontally) M2 b e n d s the b e a m 15 ° a n d refocuses it in b o t h planes a t a point a b o u t 8 m e t r e s from t h e PS t a r g e t w i t h a magnification of 1.6 h o r i z o n t a l l y a n d 2 5 vertically B o t h m a g n e t s M1 a n d M2 are fitted with a d d i t i o n a l coils in u n i f o r m field sections so t h a t the b e n d i n g can be v a r i e d by a few p e r cent while the focusing is kept c o n s t a n t A more detailed report on these m a g n e t s will be p u b l i s h e d elsewhere 2) A t the first focus t h e m o m e n t u m dispersion is 1 6 cm a n d 4 6 m r a d for a 1 % change in m o m e n tum* A n a d j u s t a b l e m o m e n t u m slit is placed at the first focus (S in fig i) I t is followed b y a 1-metre b e n d i n g m a g n e t M3 giving 10 ° deflection, three 1m e t r e q u a d r u p o l e s Q1, Q2, Q3 a n d a 2-metre b e n d -
SECONDARY
PARTICLE
BEAM
69
planes a n d gives a good m o m e n t u m transmission A n image with v e r y good c h r o m a t i c correction has been o b t a i n e d a t 22 m from the PS t a r g e t Act u a l l y t h e b e a m size at this position, m e a s u r e d directly w i t h a Polaroid 3000 speed film a n d also with scintillation counters, appears to be a b o u t 1 to 2 cm 2 w h e n using a 1 cm a p e r t u r e m o m e n t u m s h t a n d increases b y only a factor 2 in area w h e n the m o m e n t u m slit IS opened to 10 cm This Increase is purely due to c h r o m a t i c a b e r r a t i o n s a n d agrees well w i t h t h e calculation The b e a m optics are shown schematically in fig 4 D u r i n g the design stage b e a m optics calculations were carried out with b o t h a n analogue a n d a digital c o m p u t e r usmg a p r o g r a m m e called T R A M P s) Quadrupole a p p r o x i m a t i o n s were used for t h e sections of the strong focusing b e n d i n g m a g n e t s The calculations were checked with
22m
II "]
k'IOhIENTUMsLIT
I
.
FOOUN CP5 TARGET
,5 2
I'1f
Q¢
02
Q..~
/"/2
~ .
S! Fig
4 S c h e m a t i c r e p r e s e n t a t i o n of t h e b e a m envelope m t h e horizontal plane T h e d a s h e d hne indicates t h e t r a l e c t o r y of a particle of h i g h e r m o m e n t u m which s t a r t e d a l o n g t h e m e a n a x i s of t h e b e a m
lng m a g n e t M4 These c o m p o n e n t s are all s t a n d a r d C E R N u n i t s The q u a d r u p o l e s can be used as a s y m m e t r i c a l triplet to provide a d o u b l y focused image at a c o n v e n i e n t p o m t b e y o n d the final b e n d i n g m a g n e t The final b e n d i n g angle (20 ° ) h a s been chosen so as to give a n a c h r o m a t i c image at the required distance along the b e a m T h e use of a triplet keeps magnifications fairly low in b o t h
floating wlre measurements, including a verification of the position of t h e first focus a n d the dispersion The t o t a l b e a m Intensities were m e a s u r e d with a n ionization c h a m b e r a n d b y s c a n n i n g across the b e a m with two r e m o t e l y m o v a b l e scintillation counters of 0 25 cm 2 area The results w i t h t h e v a c u u m c h a m b e r all along t h e b e a m are given in
* T h e t o t a l m o m e n t u m acceptance of ~ 2 5 % ]s h m l t e d b y t h e h o r i z o n t a l a c c e p t a n c e of the q u a d r u p o l e s I t could be m a d e ~ 50 o~ l a r g e r b y p l a c i n g a q u a d r u p o l e n e a r e r to the first focus, b u t a l a r g e r m o m e n t u m b a n d w a s n o t required for t h e e x p e r i m e n t s a t p r e s e n t planned
3) M Barbler, L Chareyre, G Petruccl, M S z e p t y c k a and L Sohnas, C E R N 62-24 3) j W G a r d n e r a n d D ~,Vhxteslde T R A M P T r a c k i n g and Matehmg Programme NIRL/M/21 National Institute, Hatwell, J u l y 1961 III
BEAM TRANSPORT
M BARBIER el al
70
fig 5 T h e c i r c u l a t i n g p r o t o n s were accelerated to 19 2 GeV/c a n d i n t e r a c t e d w i t h a Be t a r g e t in the s h a p e of a 1 m m wire, 20 m m long in t h e proton b e a m direction W i t h o u t the v a c u u m chamber m M1 a n d M2 t h e m t e n s l t y s h o u l d b e l a r g e r b y a b o u t a f a c t o r of t w o T h e t o t a l i n t e n s i t i e s agree w i t h d a t a f r o m this l a b o r a t o r y 4) a n d f r o m B r o o k h a v e n 5) T h e l o w e r = - i n t e n s i t y r e l a t l v e to t h a t for =+ is p a r t l y d u e to t h e effect of t h e PS f r m g m g field m
.lo-1
//
RATIO
at PS internal target
// //
10-2
K"
--p--
at 22 m T,J•**,
/////:at22m -
2406
/
//'~
\
1
B'*
2
GeV/e
3
Fig 6 Particle ratios as measured at 22 m from the target
and corrected for decay to give ratios at the target
106
~/
1
2G~,/c
3
Fig 5 Intensities observed per 1011 clrculatmg protons Protons of 192GeV/c struck a Be target Measurements were made 22 m from the target
zJp[p = ± 2 5 %
be i n c r e a s e d s o m e w h a t b y displacing t h e t a r g e t r a d i a l l y o u t w a r d s H o w e v e r , since t h e r e still r e m a i n s a n excess of pomt~ve p l o n s we w o u l d t e n t a t i v e l y i n t e r p r e t it as a difference in yield at the target Particle a b u n d a n c e s as m e a s u r e d w i t h a D I S C C h e r e n k o v c o u n t e # ) are s h o w n in fig 6
t h e v i c i n i t y of t h e t a r g e t A t 1 GeV/c t h i s p r o d u c e s a difference of 0 7 ° b e t w e e n t h e p r o d u c t i o n a n g l e s for p o s i t i v e a n d n e g a t i v e particles, r e s u l t i n g m a difference in i n t e n s i t i e s of a b o u t 10 % P r e l i m i n a r y m e a s u r e m e n t s s h o w e d t h a t t h e ~ - m t e n s l t y could
Acknowledgements
4) A Dlddens, E Llllethun, G Manning, A E Taylor, G I Walker and A Wetherell, private communication 5) R L Cool, private commumcatlon
6) R Meumer, J P Stroot, B Leontlc, A Lundby and P Dutell, Nucl Instr and Meth 17 (1962) 1
W e are i n d e b t e d to P Dutell, T A R o m a n o w s k l , N W h y t e a n d E J N W i l s o n w h o p a r t i c i p a t e d in s e t t m g u p the b e a m
DISCUSSION
Could you explam why the ywld of antxprotons is not increasing at smaller angles ~ JENTSCHKE
DOWELL I t has been reported by Droblewskx at the High Energy Conference that the average transverse too-
mentum mcreases wxth mcreasmg parhcle mass The productxon of heavier partxcles ts therefore less peaked m the forward dtrectlon As far as I know there is no theoretical explanatxon for this