Flat Bunches for the LHC Luminosity Upgrade towards 10 35 cm -2 sec -1

Flat Bunchesfor the LHC Luminosity Upgrade

towards 1035 cm-2sec-1

Chandra BhatFermilab

LARP CM13 Collaboration MeetingNovember 4-6, 2009

Port Jefferson (Hosted by BNL)

Acknowledgements

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Frank Zimmermann, Oliver Brüning, Elena ShaposhnikovaHeiko Damerau Gianluigi Arduini Inputs on beam instability

in LHC upstream accelerators Elias Metral, Giovanni Rumolo

LHC Operation Group

J. MacLachlan (ESME simulations)

LARP CM13 Meeting, Nov. 4-6, 2009, Chandra Bhat

LHC upgrade paths with L 1035 cm-2sec-1

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early-separation dipoles inside detectors → hardware inside ATLAS & CMS detectors, first hadron crab cavities; off- , =3.75m

J.-P. KoutchoukEarly Separation (ES)

۞ crab cavities with 60% higher voltage → first hadron crab cavities, off--beat =3.75m

Full Crab Crossing (FCC)

۞ long-range beam-beam wire compensation → novel operating regime for hadron colliders, beam generation

=3.75 m

Large Piwinski Angle (LPA)

smaller transverse emittance → constraint on new injectors, off--beat

=1 radian

R. GarobyLow Emittance (LE)

L. Evans,W. Scandale,F. Zimmermann

(F. Zimmermann, CARE-HHH Workshop, 2008)

F. Ruggiero, W. Scandale.F. Zimmermann

Small-Angle

Crab CavityI=1.7E11ppb# of Bunch=2808Bunch Spacing=25ns*~10 cm Small-A

ngle

Crab CavityI=1.7E11ppb# of Bunch=2808Bunch Spacing=25ns*~10 cm

Wire

CompensatorI~6E11ppb# of Bunch=1404Bunch Spacing=50ns*~25 cm

I=1.7E11ppb# of Bunch=2808Bunch Spacing=25ns*~10 cm


ECLOUD Simulationsfor Gaussian and Flat bunches

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Nominal LHC Beam

Ultimate LHC Beam

Without satellite

Humberto Maury Cuna, CINVESTAV, Mexico

Average Heat Load 2nd Batch

Without satellite 50 nsec

Conclusions: The estimated heat load from the e-cloud effects on LHC cryogenics with flat bunches is about two times smaller than that with Gaussian bunches at the same bunch int..

Frank Zimmermann (CERN) and Humberto Maury Cuna, (CINVESTAV, Mexico)


“Flat Bunches” Types and Generation

Flat Bunches come in two forms

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There are two distinct methods to create flat bunches Barrier rf Resonant rf systems

Double, triple or multiple harmonic rf system Longitudinal hollow bunches, Carli’s technique

E

t

E

tand

tt

Smaller

E

Larger E


Flat Bunches in the Fermilab Recycler(2000 - Present)

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9.3 sec

Single Flat Bunch Two Flat Bunchesof unequal Int.

RF

Line-charge Distribution

Multiple Flat Bunchesof unequal Int.

Broad-band RF Cavities#of Cavities=4,

Vrf=2kV, 10kHz-100MHz,

Rs~50,

tV

RF Waveforms

Beam

Measurements35% drop in peak int.25% drop in E for

flat bunches


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SPS Studies:

RF h Vrf(MV) Ratio V4/V1

200MHz 4620 1-2

800Mhz 18480 0.1-0.5 0.25

Bucket Length=5 nsec

Range of Vrf in the Experiment

E 26 GeV and 270 GeV

E. Shaposhnikova, T. Bohl, T. Linnecar, C. Bhat, T.Argyropoulos*, J.Tuckmantel

November 2008

0.9nsec

1.22nsec

h2/h1=4

Conclusions (for h4/h1=4) : BLM is unstable under almost all time & BSM is more stable almost all time.

Experiment with a single harmonic rf wave also showed the signs of instability(?!?).

More studies are being carried outLARP CM13 Meeting, Nov. 4-6, 2009, Chandra Bhat

Single Bunch, Local Loss of Landau Damping

BSM V4/V1=0.25, Beam Energy = 270 GeV# of Bunches = 1-4, Intensity1E11 (L=0.4 eVs)

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10 MHz RF system only, 32 kV at h = 21 Vrf(h=21)=31kV and Vrf(h=42)=16 kV

Bunches in single harmonic RF Bunches in Double harmonic RF

h Vrf

21 32kV

42 0

h Vrf

21 32kV

42 16kV

Flat Bunches

Std. Bunches

C. M. Bhat, et. al., PAC2009

ConclusionsBeam in h=21 showed coupled bunch oscillationsBeam in DOUBLE HARMONIC rf became stable (~for 120 ms)

Last two bunches

LE(4)= 1.45 eVs

I=840E10/batch

PS Studies at 26 GeV: C. Bhat, H. Damerau, S. Hancock, E.Mahner, F.Caspers

h = 21 h = 21+42


using LHC25

Stable Flat Bunches using Double-harmonic rf System

h2/h1=2V2/V1=0.5

Beam Stability Criterion

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No Landau Damping

Stable Beam

• Large synchrotron frequency spread improves the stability.

• If inside the bucket, particles in

the vicinity of this region can become unstable against collective instabilities.

• As the slope of the rf wave is reduced to zero at the bunch center, the bunch becomes longer and synchrotron frequency spread is greatly increased. This increases Landau damping against coupled bunch instabilities.

0dtdf s

V. I. Balbekov (1987)

A. Hofmann & S. Myers, Proc. Of 11th Int. Conf. on HEA, ISR-Th-RF/80-26 (1980)

21

h Vrf

21 32kV

42 16

fsyn

/fsyn

(h=1

@bu

nch

leng

th=0

)

July 09 Study

November 2008 Study


Flat Bunch Prospects for LHC(Simulation Studies with ESME)

Two scenarios for creating flat bunches at LHC have been investigatedFlat Bunches at 7 TeV using

400 MHz + 800 MHz RF200 MHz + 400 MHz RF systems in the Ring

Flat Bunches creation at 450 GeV and acceleration

11LARP CM13 Meeting, Nov. 4-6, 2009, Chandra Bhat

Flat Bunches in the LHC at 7 TeV with 200 MHz and 400MHz rf

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Vrf(400MHz)=8MV

E vs t

Normal Bunch

2.5 eVs

E vs t

Vrf(200MHz)=3MV Vrf(400MHz)=1.5MV

Flattened Bunch

2.5 eVs

Mountain RangeTime for flattening 10s Remark:

Required 200 MHz rf cavities exist. R. Losito et. al., EPAC2004

Conclusions: The flat bunches are stable for l 2.5 eVs lb 75 cm in the case of 200MHz+400MHz rf.lb38 cm in the case of with 400MHz +800MHz rf.Calculated drop in

Peak int. 25% E 15%


ESME Simulations

LPA Scheme – Some Options

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Parameter Ultimate

bunch intensity bunch spacing

1011

ns1.725

4.950

6.350

5.750

LE (4) eVs 2.5 2.5 2.5 1.5Average Current I[A] 0.86 1.22 1.6 1.42* at IP1&5 m 0.5 0.25 0.25 0.25

crossing angle, P rad, Rad315, 0.75 381, 2.01 381, 3.7 381, 2.9

peak lumi ℒ average ℒ (turnaround time 5h)

1034cm-2s-1

1034cm-2s-12.31.2

10.73.5

103.8

103.6

Bunch Length (RMS) cm 7.55 11.5 22 17

Gaussian Long. Profile

(Normalized) = 3.75 m, Allowed Qsum<0.015 (LHC Design Rept. III)

LPA Scheme Bunches with Harmonic RF


RF Combination MHz 400 400+800 200+400 200+400

ProposalTheoretical Investigations of

Flat Bunch Scenarios for the LHC Luminosity Upgrade

(November 4, 2009 )

C. Bhat, H-J. Kim, F.-J. Ostiguy, T. Sen

Issues for Theoretical Investigations

Proposing to do theoretical investigations on the following issues -- For creation of flat bunches, investigate the use of multiple harmonic cavities (perhaps 2 to 3 harmonics) and barrier bucket systemSpecify

Optimal RF parameters Beam intensity limits Reevaluate impedance budget and constraints

If flat bunches are to be produced in one of the LHC upstream machines, explore beam instability issues for acceleration up to 7 TeV.Single-bunch and multi-bunch instability issues.


Issues for Theoretical Investigations (cont.)

What are the optimal bunch and beam parameters for the LPA scheme with due consideration of the following Integrated luminosity (i.e. luminosity and lifetime) Emittance growth from beam-beam interactions, IBS Instability growth rates Beam loading compensation Event pile-up: number, space and time resolution of events per bunch crossing Beam losses

Investigate possible locations and effects due the cavities in the machine lattices. A hybrid scheme that would allow the FCC scheme to benefit from some of the advantages of flat bunches. This would be worth exploring. Lower peak intensity decreases the e-cloud effect and space-charge effects Lower momentum spread Possibly better event resolution (spatial and time) in the detectors


Existing Simulation ToolsESME This is a 2D code to study longitudinal beam dynamics in (E, t)-phase space in

synchrotrons. We will use it to address Flat bunch creation and acceleration with single and multiple harmonic rf systems, Beam in barrier buckets, Longitudinal single and multi-bunch instability Beam loading issues.

Beam-beam code BBSIM This code will be used to study the impact of beam-beam interactions on the

emittance growth. Comparisons between a longitudinal Gaussian profile and a flat profile will be made for the LPA and for the FCC schemes.

Vlasov solver This will be used to investigate long term beam stability and particle losses. Also,

1) extract spectral information and 2) help establish the optimal ratio of harmonic amplitudes and bunch length, in the presence of realistic impedances.

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I have already shown some ESME simulation results. More to come


SummaryThe flat bunch scheme is a viable path for the LHC luminosity towards 1035 cm-2sec-1. But, there are a number of issues, may be unique to the LHC, that need to be investigated.The results from studies in the PS and SPS are very encouraging and more experimental work is being carried out.It will be useful to have a test 400MHz rf cavity (Vmin~2MV) in the SPS to conduct dedicated studies on beam instability in flat bunches.I have discussed viable schemes for flat bunch creation at 7TeV with 200MHz+400MHz /400MHz+800MHz

systems creation at 450GeV and acceleration to 7TeV

Some problems need to be addressed. A group is formed at Fermilab to perform in-depth“Theoretical Investigations of Flat Bunch Scenarios for the LHC Luminosity Upgrade” under LARP (0.8FTE/YEAR, for two years)


Flat Bunches with Double Harmonic RF during the Recent MDs at CERN

Studies in PS November 2008

LHC-25 cycle, Flat Bunch at 26 GeV Beam Intensity: ~8.42E12 Equivalent LHC nominal Intensity Bunch Emittance:~1.4 eVs Nominal emittance to LHC beam RF with V(h=21)=31kV and V(h=42)=16kV V42/V21~0.5, 0.0

July 2009 PS Cycle and Emittance same as above, Intensity about 15% larger RF with V(h=21)=10kV and V42/V21=0.0 to 1.0 in steps of 0.1

Studies in SPS November 2008: Study on BLM and BSM

Coasting beam at 270 GeV # Bunches =4, with bunch separation of 520 nsec Bunch intensity and emittances similar to Nominal LHC beam RF with V(800MHz/200MHz) = 0.25, with varieties of V(200MHz)

July 2009: Study on BLM and BSM Studies at 26 GeV # Bunch= 1, Varying Bunch Intensity and emittance (max. comparable to

LHC beam) RF with V(800MHz)/V(200MHz) = 0.25 and .1 , with V(200MHz)=1.7MV

LARP CM3 Meeting, Nov. 4-6, 2009, Chandra Bhat 20

Heiko Damerau Steven Hancock Edgar Mahner Fritz CaspersFrank ZimmermannChandra Bhat

Elena ShaposhnikovaThomas Bohl Trevor Linnecar Theodoros ArgyropoulosJoachim TuckmanChandra Bhat

SPS Beam Studies(cont.): BSM and BLM(Preliminary)

Both BSM and BLM scenarios showed beam blowup The instability kicked in between 0-350 sec.The order in which a bunch becomes unstable was quite randomEven though initial bunch parameters are nearly the same, they stabilized at different bunch properties


BSM Bunch 1 Bunch 2

Bunch 4Bunch 3

BLM Bunch 1 Bunch 2

Bunch 4Bunch 3

4 B

unch

Len

gth(

nsec

)

Time(sec)

Beam Studies in the PS at 26 GeV

LARP CM3 Meeting, Nov. 4-6, 2009, Chandra Bhat22

C. Bhat, H. Damerau S. Hancock, E.Mahner, F.Caspers

ESME simulations

Simulations predicted 20% increase in RMSW from beginning of rf manipulation to the flattened bunchBunches in these double harmonic rf buckets should be stable with LHC beam parameters.

Previously, the studies with double harmonic rf at PSB at CERN (A. Blas et. al., PS/ RF/ Note 97-23 (MD)) have shown beam becoming unstable, in contrast to these simulations.

Hence, more studies were undertaken in the PS

Bunch Flattening of the LHC Beam at 7 TeVwith 400 MHz and 800MHz rf


Vrf(400MHz)=16MV

E vs t

Line charge Distribution

Energy Distribution

E vs t

Line charge Distribution

Energy Distribution

Vrf(400MHz)=16MV +Vrf(800MHz)=8.5MV

Normal Bunch Flattened Bunch Mountain Range

2.5 eVs

z=7.5cm

E=3.2GeVrms=0.72GeV

lb=41cm

E=2.6GeVrms=0.6GeV

Conclusions: The 41 cm long flat bunches (2.5 eVs) with 400MHz+800MHz rf systems may be susceptible to beam instability.

Synchrotron Tune vs ½ Bunch Length

Examples from the July 09 Studies A first look


2009-07-14_LHC25_FlatTop_10kVh21_0kVh42_cb_18b_c

2009-07-14_LHC25_FlatTop_10kVh21_5kVh42_cb_18b_b

h Vrf

21 10kV

42 0kV

h Vrf

21 10kV

42 5kV

Beam (4) Emittance = 1.45 eVs, Batch intensity=924E10

Beam became unstable near the end of the cycle

BL=65nsec

BL=65nsec

Flat Bunches

Std. Bunches

Flat Bunches for the LHC Luminosity Upgrade towards 10 35 cm -2 sec -1

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