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
W. Hofle / LIU review 17.11.2011
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
W. Hofle / LIU review 17.11.2011
e-cloud vertical instability
frequency
turns
sum difference (delta)
instability growingsignals up to 1.2 GHz
R. de Maria et al.DIPAC 2009, MOPD17
artifact from pick-up(beam pipe cut-off)
quadrupolar motion (longitudinal)at injectiondue to voltagemismatch
W. Hofle / LIU review 17.11.2011
e-cloud vertical instability
R. de Maria et al.DIPAC 2009, MOPD17
W. Hofle / LIU review 17.11.2011
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”
W. Hofle / LIU review 17.11.2011
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
W. Hofle / LIU review 17.11.2011
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
W. Hofle / LIU review 17.11.2011
suppression of emittance growth demonstratedhigh feedback gain required
Recent results (WARP code) – (2)
J. L. VayR. Secondo (LBNL)PAC 2011
head
tail
time(turns)
kicks
W. Hofle / LIU review 17.11.2011
Recent results (WARP code) – (3)
J. L. VayR. Secondo (LBNL)PAC 2011
need to review these parametersand agree on a set for the upgrade;address higher energies in the simulations
W. Hofle / LIU review 17.11.2011
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
W. Hofle / LIU review 17.11.2011
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)
W. Hofle / LIU review 17.11.2011
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:
W. Hofle / LIU review 17.11.2011
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
W. Hofle / LIU review 17.11.2011
New kickers short striplines, or split band approach ?location: dispersion suppressor, flat chamberfrequency reach < 1.5 GHzcabling in LS1, preparation of space
W. Hofle / LIU review 17.11.2011
Questions ?