Ring to Main Linac RTML: Status and Plans

1
Ring to Main Linac (RTML)Status and Plans

• ILC January Meeting (KEK)
• Peter Tenenbaum
• 19-Jan-2006

2
A Few Improvements

• The RTML is almost unchanged from the design
  described in the BCD
• There are a few changes which are proposed
• Move boundary of Damping Ring section to include
  damping ring extraction region (DRX)
• Proposed boundary is at zero-dispersion point at
  end of DRX
• Replace multi-wire emittance station in Emit1
  with single wire or other profile device
• Insert 610 m (approx) transfer line (DRStretch)
  to optimize DR position within site boundary
• Remove skew correction section from Emit2
• Extend Linac Launch diagnostic section (not
  quite long enough in BCD)
• Remove first diagnostic section in main linac
• Redundant with last diagnostic station in RTML!
• This talk assumes that these changes will be
  accepted, and describes the changed system

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RTML Footprint
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Basis for Estimates of Lengths and Components

• Bunch compressors lattice files of 3rd
  generation designs from 2005
• Other systems scaling from TESLA or NLC
  lattices based on changes in beam parameters, if
  any
• These estimates are necessarily rougher than the
  bunch compressors

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System Lengths
6
Magnet Counts
7
Instrumentation
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BC RF Systems

• BC1 has 3 cryomodules, 1 klystron, plus one spare
  klystron with waveguide switch
• BC2 has 57 cryomodules, 19 klystrons, of which 1
  klystron 3 cryomodules are spare
• Gradients modestly lower than 31.5 MV/m needed
• Stations operate far from RF crest
• Need to change klystron amplitude and phase
  during train to compensate beam loading
• Larger average power goes to RF loads than in
  main linac stations
• Phase and amplitude tolerances are tight
• Phase jitter lt 0.1 ? 2 loss of integrated
  luminosity from longitudinal jitter of collision
  point
• Most promising bunch length monitor requires crab
  cavity
• Based on system prototyped at SPPS and TTF2
• Might need crab cavities for bunch length
  measurement, depending on downselect of BLM
  technology

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Bunch Compressor Wiggler

• Each BC in baseline has 240 meters of bend
  magnets arranged in chicanes to generate
  compression
• Long!
• Considering two approaches to reducing length
• Enhancing R56 by forcing nonzero D at quads
• Replacing wiggler with 4-bend chicane with
  optimized lattice functions for emittance
  preservation
• Issue here is control of vertical dispersion and
  emittance growth from pitched cavities
• Studies ongoing at this time

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Beam Stops

• Current design has 3
• Low power (lt 1 kW) insertable stopper
• Somewhere in skew correction or collimation
  section need to find the best spot for it
• Allows single-bunch tuneup of beams extracted
  from DR
• Full power (220 kW and 660 kW) pulsed dumps after
  BC1 and in Linac Launch
• Allow bunch length tuneup without sending beam
  into next RF section
• Also may have machine protection role
• 3 possible modes of operation
• Train-by-train, using pulsed bends
• Intra train, with fast (100 nsec risetime)
  kickers
• Bunch stealing take 1 bunch out of train for
  diagnostic purposes (open to debate)
• Are these enough?
• Or possibly too much?
• Can we save money in pulsed systems by limiting
  their average power but allowing a large peak
  power?
• Can take a full train for MPS occasionally, or a
  fraction of a train forever

11
Spin Dynamics

• Each side has 1 complete spin rotator
• Implications
• Cant simultaneously run to 2 IRs with spin
  optimized in both
• Need 2 spin rotators per side
• Cant to train-to-train spin-flipping of
  positrons
• Would need either 2 or 4 spin rotators on
  positron side
• How important is this?
• Can we do it upstream of the DR? At 250 MeV?

12
Tunnels etc.

• Current assumption RTML is laser-straight
• Main linac is curved
• Somewhere there must be dispersion matching
  between RTML and ML
• Two parts of RTML beamline (upstream of
  turnaround and downstream) share tunnel
• Is that OK? Is it cost-optimal?

13
Collimation

• Assuming 2 phases x 2 planes x 1 iteration of
  collimation
• Spoiler survival probably not a problem
• Large geometric emittances
• Close to DR can halt extraction quickly
• Collimated halo points at BC2 and BC1 RF stations
• Is that OK?
• Assuming energy collimation in turnaround or
  bunch compressor wigglers

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Progress since Frascati

• Work started on shorter BC wigglers and
  turnaround optics
• Leaders of all Technical and Global systems
  contacted
• Notified about potentially interesting issues in
  the RTML
• Dialogue begun What do you need from us, when
  do you need it, and with whom should we be
  corresponding?
• Most TS and GS have replied already!

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Upcoming Milestones (Tentative Map)

• 20 Jan
• Finalize boundaries and other changes described
  on Slide 2
• 29 Jan
• Site layout, RF unit, PPS / MPS issues finalized
• Impact DR Stretch and other areas
• 12 Feb
• Complete optics for turnaround
• Complete optics for collimation system
• Complete optics for BC wigglers
• 26 Feb
• Complete optics for pulsed dumplines
• Select BLM technology (or technologies)

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Milestones (2)

• 12 Mar
• Complete all optics
• Select size monitor technology for Skew section
• 22 Mar
• Attend Sisters of Mercy concert _at_ Warfield in San
  Francisco
• 27 Mar
• Complete system integration of lattices
  (Woodley-fication)
• April
• Review RTML design and place lattices and
  documentation under change control