Staged implementation of high bandwidth transverse feedback system in the SPS W. Hofle

Staged implementation of high bandwidth transverse feedback system

in the SPS

W. Hofle

for LARP - CERN SPS High bandwidth feedback team

17.11.2011

W. Hofle / LIU review 17.11.2011

objective: cure transverse “single bunch” instability by feedback

two collective effects are limiting the SPS performance as LHC injector

e-cloudTMCI

similarities: both effects cause vertical intra bunch instability

high chromaticity suppresses instability to a certain extent

feedback expected to permit running at low chromaticity and at intensities beyond

which high chromaticity is a established cure

particular important to maintain small transverse emittances

Motivation


coherent signals visible for both ecloud and TMCI instability

provided reaction time (few turns) shorter than growth times feedback in principle should work

Feedback as cure

frequency

turns

sumdifference (delta)

instability growing(TMCI)signals up to 1.6 GHz

R. de Maria et al.DIPAC 2009, MOPD17


e-cloud vertical instability

frequency

turns

sum difference (delta)

instability growingsignals up to 1.2 GHz


artifact from pick-up(beam pipe cut-off)

quadrupolar motion (longitudinal)at injectiondue to voltagemismatch


e-cloud vertical instability



existing hardware simulated, no cables

simulated, with cablemeasured responseultra-short bunch

forward(BPW 321.01)

backward(BPW 319.01)now kicker

pick-up, also used as kicker since this yearlooking in beam direction“forward”


simulations have focused up to now on ecloud instability

initial study done in 2008 with headtail (J. Thompson et al.)this study showed feasibility in principle, but simple FB modelfocused on 55 GeV (SPS injection with PS2)

repeated since using WARP code (J. L. Vay, R. Secondo et al.)

future: CMAD (C. Rivetta et al.) ?

TMCI best accessibly through headtail due to good modeling of SPS Impedance in this codere-launch simulations with headtailalso look at interplay of impedance and e-cloud

Feasibility of feedback in simulations

J. Thompson et al.CERN-AB-2008-070PAC 2009 FR5RFP076


suppression of emittance growth demonstratedhigh feedback gain required

Recent results (WARP code) –(1)

J. L. VayR. Secondo (LBNL)PAC 2011

emittanceincrease

growth Suppressedfor G=0.2

no feedback


suppression of emittance growth demonstratedhigh feedback gain required

Recent results (WARP code) – (2)


head

tail

time(turns)

kicks


Recent results (WARP code) – (3)


need to review these parametersand agree on a set for the upgrade;address higher energies in the simulations


Limitations of the simulations

action of feedback can only be followed over a very limitednumber of turns in the simulations

difficult to quantify the impact of numerical noise on the estimation of the required kick strength and the emittance growth; incoherent effects in case of e-cloud hard to quantify

multi-bunch effects neglected so far

more simulations will give us only an incremental increase in confidence with regards to the feasibility

adopt a staged experimental approach


Boundary conditions:LS1: 2012LS2: 2017+

Phase 1: The demonstrator end 2012 minimum goal: damp head tail motion of single bunch existing equipment (amplifiers, BPWs as kicker and PU) electronics (LARP), close FB loop

all design specifications for phase 2: end of 2012

Phase 2: New pick-up, new kicker, consolidated electronics, higher power amplifiers, preparation of LSS3 in LS1 for installation of equipment at the end of LS1 or later in a short winter

shutdown post-LS1 feedback on multi-bunch beam in presence of e-cloud decide on final implementation and LSS3 vs. LSS5 before

LS2

R&D and staged implementation: The Path (1)


Phase 3: Final implementation in LS2

depending on desired energy range upgrade powerand if impossible to install in LSS3 for reasons of space or

radiation move to LSS5

add kicker modules if required

design and construct final electronics (profit from latest technology)

commission after LS2

R&D and staged implementation: The Path (2)

(a) schedule

new pick-up design and construction

Year 4Year 3Year 2Year 1 Year 5

Phase 1:

20172014201320122011 2015 2016 2018Year 6 Year 7

demonstrator

power amplifiers for phase 2 tendering (s)

kickers design and construction

phase 2 beam testsPhase 2:

go/no-gophase 2:

Phase 3: implementation

go/no-go phase 3:


New pick-up

long precision coupler (separate the “reflection”)reserve 2 m space close to a QD in LSS3 (straight

section)free space during LS1 (reshuffle some equipment,under discussion with Eric)install cabling in LS1 and dummy chamber if PU not

readyfor highest frequency reach go for smallest diametercircular vacuum chamber (define with ABP when location decided)E. Montesinos interested in design and fabrication, lead time (!)

E. Montesinos

PUkicker


New kickers short striplines, or split band approach ?location: dispersion suppressor, flat chamberfrequency reach < 1.5 GHzcabling in LS1, preparation of space


Questions ?

Staged implementation of high bandwidth transverse feedback system in the SPS W. Hofle

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