J-P%20Koutchouk

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Two Interesting ProjectsThe AC DipoleThe
Long-range Beam-Beam Compensator

• J-P Koutchouk

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AC DipoleOutline

• Motivation
• Principle
• Preliminary Results at Cern,
• AC Dipole Parameters
• Conclusions

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Motivation

• Excite transversely the beam to study its
  response without the drawback of decoherence and
  emittance blow-up (hadrons). This is especially
  important for LHC the anharmonicity due to the
  magnetic field multipoles induced by the
  persistent currents in the s.c. material may be
  large producing a fast decoherence.
• Small amplitudes, for the study of linear optics
  (Twiss parameters, coupling, dispersion,...),
• Large amplitudes to study the non-linearity.

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Principle

• Studies carried out at BNL/AGS and RHIC by M.
  Bai, S.Y. Lee, S. Peggs et al., first for spin
  manipulations.
• Excite transverse forced oscillations of the beam
  with anAC dipole whose frequency is close but
  outside the beams eigen-frequencies.
• If the excitor tune is m/n, the beam may be
  viewed as circulating on a closed orbit which
  closes over n turns.
• The equilibrium oscillation amplitude is given
  by

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Example at Cern using the SPS damper
SL-Note-00-062 MD O. Berrig, W. Hofle, R. Jones,
J. Koopman, J.P. Koutchouk, F. Schmidt, MD 2001
A. Burns, J. Klempt
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Amplitude and Emittance versus Excitor Frequency
Beam
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Implementation at LHC

• Linear measurements Use of the LHC damper to
  excite the beam. 1 BPM provided on each side of
  the damper.
• Large amplitude measurements 4 AC dipoles
  needed.
• Parameters look feasible (O. Berrig, H.
  Schmickler) 2 times the strength of the RHIC AC
  dipole. Resonant circuit 1KA, 400V, 1 KW at 3
  KHz, adjustable bank of capacitors

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Conclusion and Prospects

• The AC dipole principle is very well adapted to
  the LHC constraints, especially at collision
  energy.
• For this reason, we are testing the principle
  with the SPS damper.
• Linear measurements in LHC The LHC feedback
  system may be used as an AC dipole. A few BPMs
  were added to allow for Q measurements.
• Non-Linear Measurements hardly any experience
  world-wide we plan experiments with the SPS. RD
  on implementation of an AC dipole for LHC to be
  launched.

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Long-Range Beam-beam CompensatorOutline

• Motivation
• Principle
• Simulation Results
• Parameters of the BBLR Compensator
• Conclusions

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Motivation

• At the nominal performance level, the long-range
  beam-beam effect has been recognized for long to
  be the limiting mechanism.
• The enlarged crossing angle (300 mrad, i.e.
  9.5s average separation) and the alternate
  crossing (cancellation of the linear tune shift)
  do not appear to leave a sufficient aperture
  where the beam motion is well behaved (Beam-beam
  workshops Cern 1999, Fermilab 2001).
• Proposal made of an active system to cancel the
  non-linear LRBB kicks (LHC Project Note 223
  PAC01).

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Principle

• A straight conductor at 9.5s from the beam
  (transverse) simulates the other beam magnetic
  field to 4 (1 averaged over the betatron angle)
  in the useful aperture it can be used to cancel
  the LR beam-beam kicks.
• The topology must be identical for the BB kicks
  and for the correction (separation, plane, aspect
  ratio, i.e. identical ratios of the b functions)
  no phase shift.
• The integrated corrector current is simply -the
  integrated (other) beam current nominal 1 meter
  80 Amperes.
• The corrector need not be pulsed for normal
  bunches.

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Position of the Correctors
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Position of the Correctors

• To correct for all non-linear effects (detuning
  is insufficient), the correction must be local.
• Layout 41 m upstream of D2, both sides of
  IP1/IP5

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Simulation Results

• .16s
• .005s
• .016s

Beam separation at IP
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Implementation Studies

• Miniteam J.P. Koutchouk, G. de Rijk, F.
  Zimmermann
• Robustness with respect to parameters (FZ) no
  critical parameter except noise on the current if
  relevant.
• Move the corrector beyond the aperture limit
  Try 12s for its center and 1s radius (1s1mm).
  May require a distribution of wires at a radius
  of 12s.
• Extract the heat enlarge corrector
  cross-section, passive or active cooling.
• Moving mecanisms and straightness of the
  corrector.
• Vacuum vessel and impedance minimization.

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Moving out the corrector at 12s and scaling up
its current
16/11/01, F. Zimmermann
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Implementation Studies

• DC version normal bunches are corrected but not
  the PACMAN bunches. A simple standard LHC PC(s)
  can do the job (100A).
• Pulsed version rise time is 15 bunch periods.
  Feasibility studied by G. Schroeder just OK with
  available switching components.

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Conclusion

• The long-range beam-beam correction scheme
  received strong support from the latest BB
  Workshop. It appears to have more potential than
  the e-lens device. Interest was expressed as well
  by Fermilab.
• In order to be ready to build the correction
  scheme when the machine approaches nominal
  performance, RD studies are to be carried out
  actively.