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IS IT POSSIBLE TO INCREASE THE p INTENSITY FOR CNGS BY A FACTOR 2 OR 3 ?

R. CAPPI / SL Seminar, 21.03.2002

• Introduction• Main limitations (some of)

– acceptances & emittances– space-charge

• double batch injection• bunch flattening

– 5 turn Continuous Transfer• new 5t CT

• List of various schemes• Conclusion

2

Introduction

• The talk is a ‘simplified’ summary of the paper: CERN/PS 2001-041 (AE) or CERN/SL 2001-032

• speculations => studies & experiments • all results are PRELIMINARY and generally OPTIMISTIC

• the talk will be mainly devoted to PSB-PS issues

• I will not talk about collective effects ( except sp. ch.), longit. beam dynamics issues , transition crossing, etc.

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Introduction: basic limitations

• NB: The present scheme is “consistent” – i.e. LINAC, PSB, PS and SPS are all close to their limits,

• i.e. there is not a single weak point• Linac2

– Close to its max Ip• PSB

– Space charge ~limited – Ek,max limited (1.4GeV)

• PS – Acceptance ~limited– Space charge ~limited– 5t Continous Transfer– ….

• SPS– Acceptance limited– ….

• Common: T & L collective effects, losses, transition, PRF , etc.

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Acceptance & emittance issues

transv. emittances at PSB extraction vs PS total intensity

0

5

10

15

20

25

30

0 1 2 3 4 5Nt [10+13 ppp]

Ex2

, E

y2 [

10-6

m]

PS acceptance: Ax=60m, Ay=20m x2 < 22m, y2 < 9m

LHC ~ 5 5

Ex2

Ey2

Ay limit

Ax limit

Courtesy of R.Steerenberg

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Present scenario & associated problems

PSB

PS

SPS

50 MeV

1.4 GeV,

14 GeV/c; 5t CT ;

x= 25

y= 12

x< 22

y< 9

x< 3

y< 2

Nt = 3

x= 4.2/3 = 1.4

y= 2.5

X

Nt = 4.8

Nt = 3.3

Q x,y~ 0.13 , 0.23

NB: in all transparencies:

1) x= 4x2/x in m

2) intensities Nt are in 10^13 p

3) is the transfer efficiency

4) p is the p flux on target in 10^13p/s

filling time = 1.2sp = 4.8/6 = 0.8 G = 1

L2Limit

Limit

G.Arduini

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Space charge (at low energy in the PS)

32,

, yx

pyx

IQ Self field tune shift:

In the PS, to be safe : 3.0Q

If : T=1.4 GeV, x = 22m, y = 9m Nt < 4.8 E13 p/p(Kb=8)

to reach it WE NEED A DOUBLE BATCH INJECTION

NB: the SPS filling time will increase by 1.2 s (or 0.6 s if PSB can pulse 2x faster* )

PS LIMIT

*) M.Benedict et al. , undergoing study

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Double batch injection into PS: forecast

PSB

PS

SPS

L2 50 MeV

1.4 GeV; 1

14 GeV/c; old 5t CT;

x= 21

y= 9.2

x< 22

y< 9

x< 3

y< 2

Nt = 4.8 => Intensity limit

for a PS @ 1.4 GeV

x= 3.4/3 = 1.13

y= 1.4

Nt = 7.7

p = 7.7/7.2 = 1.07 G = 1.34p = 7.7/6.6 = 1.17 if PSB@.6s, G = 1.46

Nt = 2 x 2.4

Q x,y~ 0.21 ; 0.35

Limit

LimitX

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Recent results of high intensity double batch injection studies

Time (ms)

Beam

intensity

( E10 p/p)

1st batch 2nd batch

Courtesy E. Metral

PS transformer

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Comparing with LHC “ultimate beam”

Time (ms)

Beam

intensity

( E10 p/p)

Courtesy G.Metral,E. Metral

PS transformerQ = 0.20, 0.26

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Can we improve space charge limits?

• Increase injection energy (e.g. with SPL)

) ) 6.2

GeV4.132

GeV2.232

• Reduce Ip by ‘bunch flattening’ techniques:

(gain <1.5)

time

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A new bunch flattening technique (*)

(*) C.Carli /CERN-PS-2001-073-AE

and EPAC2002

12Courtesy C.Carli

Q reduction of ~28%

Bunch flattening in PSB: recent resultsInitial bunch Final bunch

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5 turn Continuous TransferIt is the way the PS uses to fill the SPS (at 14 GeV/c)

CSPS = 11 x CPS

PS PS

SPS

x’

x1

2

3

4

5

Qx = 6.25

ES blade

Present system:

+ it works

- it is lossy (~20%)

Extracted beam

time, 2s / div

.TT2 transfo1 2 3 4 5

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Proposal for a new 5t CT (*)

The principle:1) the beam is adiabatically captured into 4 islands of a 4th order resonance properly adjusted with sextupoles and octupoles,

(*) M.Giovannozzi, R.Cappi ; Phys. Rev. Lett., V.88, i.10

Initial state

Simulation results

Final state

Simulation results

2) then the beam is extracted similarly to the present scheme.

ES

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n 5t CT: pro / con

+ it should be less lossy (~5%)

+ the five beamlets will match the phase space topology better =>

less betatron mismatch at injection in the SPS=> lower transv. emittance beam to SPS =>

lower losses => higher intensity

- it has to be tested experimentally

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n5tCT: (x, x’ ) topology

Courtesy M.Giovannozzi0.244

0.245

0.246

0.247

0.248

0.249

0.25

0.251

0.252

0.253

0 2000 4000 6000 8000 10000 12000 14000 16000 18000

Turn number

Fra

ctio

nal

tu

ne

a) Initial state: no islands

Extraction

c)Transport within islands

Mixing

b) Capture process

qx

time~ 30 ms

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n5tC

T:

x-x

’ m

easu

rem

en

t re

su

lts

Court

esy

M.E

.Angole

tta, A

-S.M

ulle

r, M

.Mart

ini,…

)

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MAD simulations

Courtesy A-S.Muller

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Courtesy A-S.Muller

MAD simulations (suite)

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Expected results from: double batch+ n5tCT

PSB

PS

SPS

L2 50 MeV

1.4 GeV,

14 GeV/c; new5t CT;

x= 21

y= 9.2

x< 22

y< 9

x< 3

y< 2

Nt = 4.8

x= 3.4/5 = 0.68

y= 1.4

Nt = 8.6

filling time = 2.4sp = 8.6/7.2 = 1.19 G = 1.49p = 8.6/6.6 = 1.30 if PSB@.6s G = 1.63

RMKS: 10% improvement => =>lower transfer losses, better matching, etc.

Nt = 2 x 2.4

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What about the SPS ?

• Single bunch coll. effects:– 8.6E13ppp => 2 E10 p/b [LHC~10 E10; e-cloud > 4 E10 (5ns?)]– Transverse impedance strongly reduced since 2002 => ~OK

• Beam loading:– 8.6E13ppp => 0.4 E13/s [ LHC~0.5 E13p/s] ~OK – better if p=26GeV/c –

• Transv. & long. Feedbacks– HW modifications? 20=>100 MHz?

– octupoles :YES (some x,y b.u. accepted) ~OK ?

• Transition:– now 5% losses, – better if p=26GeV/c

– Etc.

K.Cornelis, T.Linnecar, E.Schaposnikova,…

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The various schemes

# Description N sps [1013p/p]

POT flux [1013p/s]

Gain = / 0.8

~Cost~ [MCHF]

Remarks

0 present nominal scheme (reference)

4.8 4.8 / 6 = 0.8 1 0 Already difficult

1.1 =0 + double batch PS inj. 7.7 7.7 / 7.2 = 1.07 1.34 0 Higher Nsps but longer cycle

1.1a 1.1 + PSB @ 0.6s 7.7 7.7 / 6.6 = 1.17 1.46 1 Important HW modifications (?) Improvements for ISOLDE

1.2 1.1 + new5-turnCT 8.6 8.6 / 7.2 = 1.19 1.49 1 Better transfer efficiency (lower losses)

1.2a 1.2 + PSB @ 0.6s 8.6 8.6 / 6.6 = 1.30 1.63 2 Best of group 1

1.3 1.2 + 26GeV/c 8.6 8.6 / 8.4 = 1.02 1.28 3 No transition in SPS CT @ 26GeV/c ?

1.3a 1.3 + displaced & shortened PSB cycle

8.6 8.6 / 7.2 = 1.2 1.5 3 Very attactive

2.1 1.2 + a new H- 120MeV Linac

8.6 8.6 / 6 = 1.43 1.79 60 Improvements also for LHC, ISOLDE,…

3.1 SPL at 2.2GeV + new 5-turnCT at 14GeV/c

23 23 / 6 = 3.83 4.79 300 Extremely high coll. effects =>UNREALISTIC

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Conclusion

• first studies show encouraging results not only for CNGS but for LHC itself and for cleaning up the machines by improving reliability

• a gain in p flux of ~1.5 seems feasible though difficult (cost ~0-2MCHF)

• a gain of ~2 is maybe possible but will be more expensive (~50MCHF)

• a gain of 3 will be VERY expensive ( ~300MCHF) and probably technically unrealistic

• we need a.s.a.p. clear priorities to continue at efficient speed.