Berkeley Lab Generic Presentation

1
Dogbone RLA Design Choices
Alex Bogacz

• Dogbone configuration
• orbit separation
• simultaneous acceleration of both m m- species
• 12.5 GeV Two-step-Dogbone RLA
• Quadrupole focusing scheme Triplet vs FODO
  lattices
• multi-pass linac optics
• droplette Arcs
• matching to the Arcs
• 5 GeV Dogbone RLA (3.5 pass) Complete lattice
  design, sensitivity studies
• 15 GeV Dogbone RLA (6.5 pass)?

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Simultaneous acceleration of both m m- species
E0
E0 (n½)DE
DE
orbit separation, energy difference between
consecutive passes 2DE
3
12.5 GeV Two-step-Dogbone RLA
the same energy ratio for both dogbones
5 GeV to 12.5 GeV
2 GeV to 5 GeV
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12.5 GeV Two-step-Dogbone RLA
the same energy ratio for both dogbones
5 GeV to 12.5 GeV
2 GeV to 5 GeV
5 GeV
1 GeV/pass
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Injection double-chicane
m
m-
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Initial beam emittance/acceptance after cooling
at 273 MeV/c
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Pre-accelerator - different style cryo-modules
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Introduction of synchrotron motion in the initial
part of the linac
Dp/p?0.17or Df ?93 (200MHz)
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Linear Pre-accelerator Longitudinal dynamics
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Symmetric Dogbone RLA (3.5-pass) Scheme

• Main Linac (2 GeV/pass)
• 3 droplet Arcs based on periodic cells (900
  betatron phase advance per cell)

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FODO vs Triplet focusing structure

• The same length
• The same phase advance per cell (Dfx 900 Dfy)

FODO
Triplet

• Advantages
• much weaker quads (3 times)
• shorter quads (total)
• easier chromaticity correction

• Advantages
• longer straight sections
• smaller vertical beta-function
• uniform variation of betas and dispersion

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Triplet - flat focusing' linac profile
mirror symmetry cond. (boutn binn1,and aoutn
-ainn1, n - pass index)
half pass , 2-3 GeV
Initial phase adv/cell 90 deg constant quad
grarients for the entire linac
1-pass, 3-5 GeV
phase adv. drops much faster in the horizontal
plane
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Triplet - flat focusing' linac profile
mirror symmetry cond. (boutn binn1,and aoutn
-ainn1, n - pass index)
2-pass, 5-7 GeV
phase adv. drops much faster in the horizontal
plane
3-pass, 7-9 GeV
no phase adv. in the horizontal plane
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FODO - flat focusing' linac profile
mirror symmetry cond. (boutn binn1,and aoutn
-ainn1, n - pass index)
half pass , 2-3 GeV
initial phase adv/cell 90 deg fixed gradient in
all cells
1-pass, 3-5 GeV
phase adv. drifting uniformly in both planes
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FODO - flat focusing' linac profile
mirror symmetry cond. (boutn binn1,and aoutn
-ainn1, n - pass index)
2-pass, 5-7 GeV
3-pass, 7-9 GeV
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FODO - flat focusing' linac profile
mirror symmetry cond. (boutn binn1,and aoutn
-ainn1, n - pass index)
4-pass, 9-11 GeV
5-pass, 11-13 GeV
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flat focusing' linac profile
mirror symmetry cond. (boutn binn1,and aoutn
-ainn1, n - pass index)
6-pass, 13-15 GeV
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Phase slippage in the linac
DE0 2 GeV
E0 2 GeV
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Arc 1 - Layout
Arc dipoles Lb150 gt 150
cm ang010.3283 gt 10.328 deg Nin16 gt
16 Nout2 gt
2 ang(90ang0)/(Nin-2Nout) gt 8.36
deg. Ang_outang02Noutang gt 43.77
deg. Ang_in2Ninang gt 267.54
deg. BPPIHrang/(180Lb) gt 6.537
kGauss Lring227.3 m
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Droplet Arc Optics Building Blocks

• 900 phase advance/cell inward and outward cells,
  missing dipole, empty cells

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Arc 1 Mirror-symmetric Optics
(bout bin ,and aout -ain , matched to the
linacs)
Nout2, need minimum of 3 triplets to match 6
Twiss parameters
2 cells
2 cells
16 cells
dipoles (2 per cell) Lb150 gt 150
cm ang010.3283 deg ang(90ang0)/(Nin-2Nout
) gt 8.36 deg BPIHrang/(180Lb) gt
6.537 kGauss
quadrupoles (triplet) Lcm GkG/cm 68
-0.326 125 0.328 68 -0.326
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Straight-Arc - Periodic transition
Triplet
FODO
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15 GeV Dogbone RLA (6.5 pass)
energy ratio
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15 GeV Dogbone RLA (6.5 pass)
energy ratio
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Beam Separation - Switchyard
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Summary

• Dogbone RLA preferred configuration
• better orbir separation for higher passes
• offers symmetric solution for simultaneous
  acceleration of m and m-
• FODO lattice more favorable (compared to the
  triplet) to accommodate large number of passes
• uniform phase advance decrease in both planes
• smaller variation of Twiss function easier
  match to the Arcs
• Proposed 12.5 GeV two-step-dogbone RLA (30 mm rad
  acceptance)
• 3.5 pass 5 GeV Dogbone (triplet lattices) error
  sensitivity studies
• Magnet misalignment error analysis (DIMAD Monte
  Carlo on the above lattice) shows quite
  manageable level of orbit distortion for 1 mm
  level of magnet misalignment error.
• Great focusing errors tolerance for the presented
  lattice - 1 of Arc-to-Arc betatron mismatch
  limit sets the quadrupole field spec at 0.2
• Aggressive 15 GeV dogbone RLA