MultiBunch Linac to IP Simulations Including Fast Position, Angle and Lumi Feedback Systems

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Multi-Bunch Linac to IP Simulations Including
Fast Position, Angle and Lumi Feedback Systems
Glen White (SLAC / QMUL) ILC-America SLAC, Oct.
2004

• Current status
• Improvements and further studies

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Multi-Bunch Simulations at QMUL

• Track 600 bunches through Linac, BDS and IP to
  observe dynamics of fast feedback correction (IP
  position and angle) Lumi feedback and determine
  estimate of train luminosity.
• Use PLACET for Linac simulation and MatMerlin for
  BDS (GUINEA-PIG used for IP collision).
• Model case of post-bba lattice 1 pulse of GM.
• TESLA TDR BDS currently implemented.
• Typical simulation times 60 hours depending on
  simulation parameters (per seed).
• To gauge performance for a variety of
  parameters/simulation environments/machines need
  many CPU hours.

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QMUL High-Throughput Cluster

• QMUL Test GRID cluster- http//194.36.10.1/cluste
  r
• QMUL high-throughput cluster GRID cluster
  development. Currently 348 CPUs (128 dual 2.8 GHz
  Intel Xeon nodes with 2 GB RAM and 32 dual 2.0
  GHz AMD Athlon nodes with 1 GB RAM) . Total
  available storage of 40TB. 1 Gb internal
  networking and 1Gb bandwidth to London MAN.
• Will upgrade by 2007 to 600CPUs and 100TB
  storage which will be mainly used for LHC
  computing needs.
• Boxes run Fedora2 Linux have 100 Unix Matlab
  licenses.

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Linac Simulation

• PLACET
• Structure Misalignment 0.5mm RMS y, 0.3mrad y
  error.
• BPM misalignment 25mm (y).
• Apply 1-1 steering algorithm.
• Apply y, y RMS Injection error.
• Apply RMS quad jitter in y.
• Apply structure long- and short-range wakefields.
• Use updated sr trans. wake -gt reduce off-crest
  phase in cavities from -27o to -10o.
• Generate 600 bunches (multiple random seeds).

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Linac Simulation

• Old (blue) and new (red) transverse wakefields
  (left plot)
• Vertical emittance of bunches exiting Linac for
  100 seeds (right plot). Emittance at Linac
  entrance 20nm.

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Linac Simulation

• Electron beam at Linac exit.
• Long-range wakes have strong effect on bunch
  train.
• Need to perform steering on plateux not first
  bunch- slow.

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BDS/IP Simulation

• MATMERLIN
• Random jitter on quads 35nm RMS.
• Add 1.4ppm energy jitter on e- bunches (simulates
  passage of e-s through undulator).
• Track 80,000 macro-particles per bunch.
• Feedback (Simulink model in Matlab)
• BPM error 2mm (ANG FB) 5mm (IP FB)
• Kicker errors 0.1 RMS bunch-bunch.
• IP (Guinea-Pig)
• Input macro-beam from MatMerlin BDS
  (non-gaussian).
• Calculates Lumi Beam-Beam kick.
• Produces ee- pairs -gt track through solenoid
  field and count number hitting LCAL first layer
  for Lumi FB signal.

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Example Run

• 1 s RMS injection y,y error into Linac
• 100 nm Linac and 35nm BDS RMS y quad jitter.
• Use Placet lattices with 25 emittance growth
  ( 25 nm at exit)
• Additional emittance growth for electron and
  positron linacs below
• Emittances quoted are for final bunch in train
  (plateux) (mean 27nm)

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Example Run

• Additional emittance growth after transport
  through BDS (final bunch).
• Electron worse than positron by additional 30 on
  average
• Mean IP emittances (37nm positron 44nm
  electron)

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IP Feedback

• Corrects lt 10 bunches.
• Corrects to finite Dy due to banana bunch effect.
• Vertical Beam-Beam scan _at_ bunch 150.

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IP Feedback
5 Bunch ee- Int. Signal

• Corrects lt 10 bunches.
• Corrects to finite Dy due to banana bunch effect.
• Vertical Beam-Beam scan _at_ bunch 150.

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Angle Feedback

• Angle scan after 250 bunches when position scan
  complete.
• Noisy for first 100 bunches (HOMs).
• FB corrects to lt0.1 sy

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Luminosity

• Luminosity through bunch train showing effects of
  position/angle scans.
• Total luminosity estimate L(1-600)
  L(550-600)(2820-600)/50

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Luminosity All Seeds
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Effect of Lumi-Scan

• After position scan

• After position and angle scan

• Effect of Pos Ang Lumi scans compared with
  start of pulse with FB only.
• Angle feedback gives negligible improvement

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LC Simulation Web Page

• Store all beam data from simulation runs online
• http//hepwww.ph.qmul.ac.uk/lcdata

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Summary and Future Plans

• Facility for parallel processing of accelerator
  codes set-up.
• Used to test TESLA performance with
  Fast-Feedback.
• Need to understand lumi performance optimise.
• Need to understand effect of banana bunches more
  completely- will come out of beamstrahlung
  studies (see other talk)
• Cross-checks with MatLiar.
• Crab cavity angle FB.
• New BDS lattice(s).
• Collimator Wakes.
• Model 1 TeV machine.
• Include Beamstrahlung monitoring. (see later
  talk)

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Summary and Future Plans

• Suggestions from Andrei
• Study effects of parasitic crossings on feedback
  (variance of charge structure in disrupted
  outgoing beam).
• Stability of beam affected by wakes on septum
  magnet in 500 GeV machine? (?t 337ns).
• Stability of beam affected by parasitic
  crossings at 26.4m in 1 TeV machine? (?t
  176ns).
• Include extraction line optics.
• Calculate septum wakes.
• Use GUINEA-PIG to study interaction at 26.4m
• (15mm vertical separation, 5mm vertical spot size)