Giovanni Rumolo H. Bartosik, Y. Papaphilippou

in LHC Performance Workshop (Chamonix 2012), 9 February 2012

H. Damerau, A. Findlay, S. Gilardoni, B. Goddard, S. Hancock, K. Hanke, G. Iadarola, B. Mikulec, E. Shaposhnikova

et al.

Necessary LIU studies in the injectors during 2012

Outline

2

Focus of the talk Review the progress made in 2011 with the LIU MDs and extract which questions still remain to be answered with beam in 2012

– 2011 LIU MDs by the machine – organization, distribution and

highlights → Linac2 + PSB → PS → SPS

– Questions to be followed up in 2012 – Priorities and organizational proposals – Concluding remarks

Overview 2011

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– 2011 distribution of the MD days (priority to MDs in all machines) → Floating MDs biweekly → Long dedicated blocks

during LHC TS (4x)

– Total number of available MD hours was 408 (434 on original schedule, same planned for 2012)

– Parallel MDs → PSB + PS: at least one cycle

per supercycle always available for MDs (or MTE)

→ SPS: usually one parallel MD cycle available every week day for studies (some times used for set up)

– Types of PSB MDs

1. Prepare new beams, tune and check existing beams, for the downstream machines

2. Define the limitations of the machine, improve the performance

3. Specific machine studies in view of the future upgrades

Linac2 + PSB in 2011

4

Parallel MDs

Dedicated MDs – Linac2 MDs

1. Remove hot spots found with the 2010 radiation survey

2. Run with increased beam current (180 mA)

– Types of PSB MDs

1. Prepare new beams, fine tune and check existing beams, for the downstream machines

2. Define the limitations of the machine, improve the performance

3. Specific machine studies in view of the future upgrades

Linac2 + PSB in 2011

5

Parallel MDs

Dedicated MDs – Linac2 MDs

1. Remove hot spots found with the 2010 radiation survey

2. Run with increased beam current (180 mA)

Time, resources!

– Beam dynamics questions relevant for LIU-PSB

? Continue tests with higher beam current from Linac2 ① Identify the impedance source responsible for the known instabilities

and specify transverse damper requirements ① Determine resonance diagram with tune scans at 160 MeV to optimize

placement of working point at injection with Linac4 ② Optics model based on turn-by-turn data from the available BPMs ② Study the efficiency of the resonance compensation schemes ② Space charge induced emittance blow up

Linac2 + PSB

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– LIU-PSB activities in 2012 (RF, hardware)

① Continue deployment of the digital RF control

① Test the newly installed Finemet prototype cavity hardware

PS in 2011

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Parallel MDs

Dedicated MDs – PS MDs

1. Space charge studies at 1.4 GeV and 2 GeV and tune diagrams

2. Adjustment of working point at low energy with quads and PFW

3. Fast instability at transition with TOF-like beams

4. Tune shift with intensity at injection and extraction energy

5. Electron cloud at flat top with 25 and 50ns beams

6. Limitations from longitudinal coupled bunch instabilities during the ramp and flat top

7. Batch compression scheme h=9 10 20 21

8. One-turn feedback with C11

PS: space charge@1.4GeV

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Nb (x 1010 p) ex,y (mm) 4st (ns) DQy

LHCINDIVhigh 40 1.7 90 -0.2

LHC50nom (DB) 80 1.1 180 -0.26

LHC50ult (DB) 120 1.8 180 -0.26

LHC25 (DB) 160 2.5 180 -0.26

AD 400 9.0/5.0 185 -0.28

TOF 800 12.0/8.0 230 -0.31

MD beams

LHC50 SB rebucketed

150.0-190.0 2.5-3.0 130 -0.34

LHChighbright 70 2.0 95 -0.25

Double batch LHC beams, 1.2sec @FB

Physics beams, short FB

For space charge studies @FB after bunch rotation

PS: space charge@2GeV

9 TUNE SCAN @ 2 GeV

E. Benedetto Shortened bunch @2GeV

→ DQx = -0.19, DQy=-0.27

→ Three working points analyzed

o Qx=0.15, Qy=0.196

o Qx=0.17, Qy=0.23

o Qx=0.17, Qy=0.30

- No losses - Little emittance growth

Is DQy=- 0.26 really the limit for the space charge tune spread at injection for double batch injection into the PS? Can we identify dangerous resonance lines and compensate them?

• Longitudinal coupled bunch instabilities with both 25ns and 50ns beams observed (previously also with 75ns and 150ns beams) During the ramp

At flat top when ramping down h=21 during bunch splitting

• What we have learnt about it ⇒ Instabilities during the ramp probably caused by the wide band

impedance of the 10MHz cavities

⇒ Coupled bunch mode spectrum changes between ramp and flat top

⇒ Little dependence on the number of bunches in the batch, but growth rates scale like Nb/ez

⇒ Small improvement with 2 gap relays, parking of unused cavities beneficial

• 2012 LIU-PS studies towards raising the thresholds ⇒ Additional feedback (decide if more hardware is needed after LS1)

⇒ PS/SPS transfer perhaps allow for larger ez to be injected into the SPS, optimize final bunch rotation

PS: longitudinal coupled

bunch instabilities

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PS: Electron cloud

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Systematic scans taken with

⇒ 50ns and 25ns beams

⇒ Simulation effort ongoing

0 0.5 1 1.5 20

0.02

0.04

time [us]

e-c

lou

d s

ign

al [a

.u. ] Av. intensity = 1.64*10

11 ppb

0 0.5 1 1.5 20

5

10

time [us]

Pic

k-u

p s

ign

al [a

.u.]

0 0.5 1 1.5 20

0.05

0.1

0.15

time [us]e

-clo

ud

sig

na

l [a

.u. ] Av. intensity = 1.33*10

11 ppb

0 0.5 1 1.5 20

2

4

6

time [us]

Pic

k-u

p s

ign

al [a

.u.]

50ns, 36b

25ns, 72b

0 0.5 1 1.5 20

0.2

0.4

0.6

0.8

1

Time [us]

Ele

ctr

on

clo

ud

in

dic

ato

r [a

.u]

Simulation 0 0.5 1 1.5 2

0

0.2

0.4

0.6

0.8

1

Time [us]

e-c

lou

d s

ign

al [a

.u.]

Measurement

dmax R0 Beam in the gap

Simulation 1.6 0.5 5%

Scans in bunch intensity and length done! 2012 MDs Measurements in presence of B field, study of double step bunch rotation

G. Iadarola, C. Yin-Vallgren

PS: miscellaneous

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– More LIU-PS machine studies in 2012

➀ Batch compression scheme h=9 10 20 21, acceleration, transfer to SPS

➀ Batch compression + bunch merging ➀ One-turn feedback against transient beam-loading

➁ Commissioning of transverse feedback system ➁ Head-tail instabilities on the flat bottom ➁ Transverse instabilities of short intense bunches at flat top

(electron cloud?) ➁ Impedance identification for modeling

③ Injection studies

– Upgrade studies included → Push the SPS performance with the present 25 and 50ns beams, as well

as with single intense bunches (up to 4 x 1011 ppb) → Development of low gamma transition optics (Q20) → Electron cloud mitigation techniques (a-C coating, scrubbing, clearing

electrodes) → Beam tests for a high bandwidth feedback system

SPS in 2011

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38%

41%

21%

Distribution of SPS MDs in 2011

Upgrade studies

Other MDs

Beam set up (ionand coasts)

Floating MDs 61% (efficiency slightly above 50%)

Dedicated MDs 39% (very high efficiency ~95%)

SPS: single bunch limits

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Limitations on single bunch

⇒ TMCI threshold

⇒ Emittance blow up along an LHC-type cycle

TMCI threshold @26 GeV/c (xV =0)

Q26 – nominal optics

– 2–2.5 x 1011 ppb injected → Losses around 10% → No emittance

growth wrt PS extraction

– Above 2.5 x 1011 ppb injected, large losses (20%) and emittance blow up

xV=0.25

SPS: single bunch limits

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Limitations on single bunch

⇒ TMCI threshold

⇒ Emittance blow up along an LHC-type cycle

TMCI threshold @26 GeV/c (xV =0)

xV=0.1

Q20 – low gt optics

– Q20 allows for injection of higher intensity bunches (up to 3 x 1011 ppb) → Low chroma → Losses below 10%

even above 2.5 x 1011 ppb

– Trend from injectors or space charge in the SPS?

SPS: single bunch limits

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Comparison across machines

⇒ Effect of a 3 sec flat bottom in the SPS

⇒ Small blow up + losses above 2.5 x 1011 ppb Q20 – low gt optics

Blow up above 1.7 x 1011 ppb, during flat bottom (3 to 10 sec) or during ramp? Working point optimization needed?

From measurements at 450 GeV/c (previous slide)

SPS: multi-bunch beams

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High intensity 50ns beams tested in MDs

⇒ Record intensity at flat top with Q20

⇒ Quoted transmission is from PS extraction to SPS flat top

Q20 – low gt optics

1.6 x 1011 ppb injected 1.5 x 1011 ppb at flat top

1.9 x 1011 ppb injected 1.7 x 1011 ppb at flat top

SPS: multi-bunch beams

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High intensity 50ns beams tested in MDs

⇒ Longitudinally more stable on Q20

⇒ Margin for longitudinal emittance blow up, when needed

Q26 Q20

Courtesy T. Argyropoulos

no quadrupole oscillations

50ns beam at flat top (1 batch, 1.5x1011ppb)

– Without controlled

emittance blow-up – 800MHz cavity

(V800=0.15V200)

Continue work on optimization of multi-bunch beams on Q20 (also 25ns), especially wrt longitudinal quality and CBI

Injection tests into LHC

12h sessions every week instead of 24h every 2nd week could help (at least later in the run)

SPS: electron cloud,

scrubbing or coating?

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– 2012 studies 1. Scrubbing week in W13 ☹ Perhaps negligible effect on the beam if we start like in 2011 ☹ Most interesting scrubbing techniques not possible for now

(5ns or 10+15ns spacings from PS) ☺ Testing efficiency of scrubbing with uncaptured beam ☺ Monitor and qualify beam induced scrubbing under different

beam/chamber conditions (beam observables, direct electron cloud observables)

☺ Validate simulation models on scrubbing times (like for LHC) 2. Some new setups for validation of a-C coating

– Electron cloud in 2011

1. Effects on the nominal 25ns beam have become less evident from the start

2. More studies on mitigation techniques done 3. Progress for the high bandwidth feedback system

SPS: miscellaneous

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– More LIU-SPS machine studies in 2012

➀ Tests with increased peak RF power ➀ More on Q20

Nonlinear optics model Split tunes (20, 26), coupling correction Instabilities (TMCI, ECI) Extension of Q20 to fixed target physics cycles

➁ PS-SPS transfer studies ➁ Terminate phase (1) for high bandwidth feedback studies (i.e.

close feedback loop and prove damping of head-tail modes) ➁ Impedance identification

All the machines

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– Emittance preservation across the injector chain

Systematic measurements with different beam types Define where the emittance blow up occurs

G. Arduini, LMC 12/10/2011

Closing remarks

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Prioritized lists of needed/advisable LIU studies have been detailed out for each machine

– PSB More resources desirable for the key studies

→ Resonances at 160 MeV → Origin of instabilities, efficiency of transverse feedback in the enlarged

parameter range

– PS Important questions

→ Space charge limit at injection → Feedback against CBI → Alternative production schemes – like batch compression

– SPS Redistribution of the MD time + MD follow up meetings in the frame of SPSU-BD WG in 2012 recommended → More frequent – and shorter – MD blocks to allow for more continuous

effort on Q20 optimization (with experts available) → 3 to 5-day dedicated block for scrubbing studies

THANK YOU FOR YOUR ATTENTION!