LHC IR Upgrades Workshop

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LHC IR Upgrades Workshop

• Tanaji Sen

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Luminosity and IR layouts

• Achievable ß is limited by
• ß max (aperture), IR chromaticity,
  long-range beam-beam interactions (crossing
  angles)
• Required aperture is determined by
• L (from experiments), Optics layouts,
  Energy deposition, Long-range beam-beam
• Gain in luminosity by reducing L depends on
  layout quad first option is more efficient if
  aperture is limited (JJ)
• ß (L LCGQ)2/ ß max
• If LCGQ gt L, gain by reducing L is limited
• LCGQ also depends on energy deposition

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Topics of the Workshop

• IR Layouts for the Upgrade
• WG1 IR optics, Energy Deposition and Magnets
• Goal Guidance on IR optics requirements and
  magnet parameters
• Avoiding luminosity loss due to crossing angles
• WG2 Beam-beam compensation
• Goal Define the beam-beam compensation
  experiment at RHIC and address challenges to
  compensation in the LHC
• WG3 Crab cavities
• Goal Define the crab cavity parameters for
  the LHC as well as possible, constraints on
  design and impact on beam dynamics

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IR optics layouts - 1

• Quadrupole first layout - JPK
• Uses scaling laws for quick exploration of
  parameter space
• Inputs ß, Np, Nbunches, Xing plane, L, Average
  quad length, Coil oversize factor
• Assumes 1) scaling of sextupole excitations for
  linear and quadratic chromaticities and
• 2) scaling of energy deposition
• Outputs Coil aperture, pole tip field, debris
  power, ß max, beam size, crossing angle, b6 and
  b10 coefficients,

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J.P. Koutchouk
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Beam-beam compensation

• RHIC beam-beam experiment
• LARP proposal to test wire compensation in RHIC
• Simulations of RHIC experiment, beam-beam
  interactions in LHC, multipole compensation
• Experience with the Tevatron electron lens

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RHIC experiment

• Studied at injection energy with 1 bunch and 1
  parasitic interaction per beam
• There is an effect to compensate, even with 1
  parasitic
• Drop in lifetime seen for beam separations lt 7 s
• Effect is very tune dependent

SPS t ? (d/s)5 Tevatron t d3 RHIC
t d4 or d2 measured 04/28/05, scan 4
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Wire compensation at RHIC

• Real test of the compensation principle requires
  2 beams
• Favorable location for wire has been found in
  IR6, phase advance to parasitic 6 degrees at top
  energy

Mechanical design for 125A-m and round
cross-section In near term studies, power up to
a max of 30Am.Eases cooling
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Wire compensation proposal

• FY06 Plan
• Design and construct a wire compensator (BNL)
• Beam-beam studies at top energy beam separation
  and tune scan. No wire.
• Theoretical studies (analysis and simulations) to
  test the compensation and robustness
• Install wire compensator on a movable stand in
  one of the RHIC rings in 2006 shutdown
• FY07 Plan
• Beam studies in RHIC with 1 proton bunch in at
  flat top and 1 parasitic interaction.
• Test tolerances on beam-wire separation, wire
  current accuracy, current ripple, phase advance
  to the wire.
• Simulations to match experiments
• Construct and install 2nd wire compensator and
  current modulator in 2007 shutdown.

• FY08 Plan
• Compensation of both beams with the 2 wires
• Elliptical beams at the parasitic interaction
  test robustness to changes in the aspect ratio
• Compensation of multiple bunches in RHIC with
  pulsed wire current.

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Simulations Action Items

• What predictions can we expect?
• Simulate 1 parasitic interaction at top energy.
• Is there a significant impact on the beam?
• Variation with separation of dynamic
  aperture, emittance change, lifetime,
• Simulate 1 parasitic interaction and wire.
• Is compensation effective?
• Tolerances on alignment, current strength and
  jitter, phase advance errors, non-roundness of
  strong beam,

• Test simulations models on experimental evidence
  so far
• SPS expt variation of losses with wire currents,
  tunes, separations
• RHIC experiment variation of losses with
  beam-beam separation, tune variation
• Important physics
• e.g. nonlinear fields including snakes, space
  charge, IBS, tune modulation,?

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Uses of the electron lens

• Footprint due to head-on collisions can be
  efficiently compressed with the electron lens
• Requires a location where the beta functions are
  equal
• Beam-beam interactions are a dominant source of
  emittance growth in RHIC. An electron lens in
  RHIC could help to improve performance.
• Emittance growth is determined by the strength of
  nonlinearity
• Beam tests in Tevatron (without parasitics) could
  be a useful first step.

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Crab Cavity development

• Ongoing work at KEK, Argonne, LBNL
• different damping strategies to damp the HOMs
• Issues large transverse size, low filling
  factor, too high Qs

Cavity Radial Size (43 cm)!!
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Tolerances at 1 mrad and 400 MHz
At 8 mrad and 800 MHz, tolerances on phase
stability are 4 times smaller about 1-2 orders
of magnitude smaller than achievable today. What
is the noise level at betatron frequencies?
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Crab cavity summary

• 400 MHz is best suited for LHC bunch length but
  transverse size, voltage required, phase
  tolerances etc seem to be excessive
• With 800 MHz, V 37 MV for 8 mrad
• Use advanced gradient 10 MV/m
• Active length 3.7 m x 4 (regions)
• Filling factor 0.3 gt 12 m
• Phase tolerance is 2 times more relaxed
• Paper designs could continue but making a strong
  case for crab cavities seems to be hard until and
  unless LHC operational experience demands very
  large crossing angles

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Thanks toRama Calaga, John Johnstone, Elliott
Mcrory, Nikolai Mokhov, Hasan Padamsee, Steve
Peggs. Vahid Ranjbar, Francesco Ruggiero. Mike
Syphers, Debbie Ziomek and all participants for a
successful workshop