ILC ML Emittance Tuning Update
and
Z-pole Calibration Runs
A. Latina (CERN)
K. Kubo (KEK)
LCWS 2016 – Dec 5-9 2016, Morioka, Japan
Outline
• Emittance transport has been revaluated for the updated
ILC main linac lattice
• Z-pole calibration runs: Two possible scenarios have been
considered
Option 1: Accelerating up to 46 GeV at 31.5 MV/m for the first 13%
of the main linac, and then just letting the beam coast through the
rest of the (detuned) linac at zero gradient.
Option 2: Uniformly reducing the gradient along the entire main
linac (starting at 15 GeV) to
G = 31.5*(46-15)/(250-15) ~ 4.3 MV/m
• Target emittance at the IP: εx = 10 μm and εy = 35 nm
2
Energy Profile for Z-pole runs
3
Lattice Setup – Beam params
• Latest Lattice – Laser-Straight Positron Main Linac
• Normalized Transverse Emittances at ML entrance:
– X: 8.8 μm(DR extraction, 8 μm + 10%)
– Y: 24 nm (DR extraction, 20 nm + 20%)
• Bunch length 300 micron ; ΔE/E = 1.07% ; Q = 3.2 nC
• Imperfections:
–
–
–
–
Short-range structure wakefields ; 1 μm bpm resolution
300 μm/μrad RMS quads and structures alignment error
7 μm RMS bpm-to-quad alignment error
0.25% quad strength error
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BBA Procedure
• ML divided in 10 bins w/ 10% overlap between
bins (approx 36 correctors / bpms per bin)
• BBA procedure / bin:
– 3x Orbit correction
– 3x Dispersion-Free Steering w/ 2 test beams:
(a) injection energy reduced by 5%,
(b) accelerating gradients reduced by 5%
• PLACET Simulations ; 100 random seeds
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BBA Performance, V-axis
(luminosity beam)
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BBA Performance, H-axis
(luminosity beam)
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BBA Performance, V-axis
(beam spent for positron generation)
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BBA Performance, H-axis
(beam spent for positron generation)
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ML DFS Simulation, Change final beam energy
• Main Linac, initial beam energy 15 GeV, nominal final energy 250
GeV. Old lattice (“2007b”)
• Uniform gradient in whole linac
– Final energy 250,200,150,100,75, 45 GeV
• Set random independent errors (Gaussian)
– Q offset 0.36mm, Cavity offset 0.67 mm, Cavity tilt 0.3mrad,
BPM resolution 1 um
• DFS correction
• Look at emittance growth at the end of linac
– (initial emittance = 20 nm)
– 40 random seeds
20161201 K.Kubo
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Emittance growth vs. final energy
Average of 40 random seeds. Error bar: standard deviation.
1.4
1.2
/
1
0.8
0.6
0.4
0.2
0
0
50
100
150
200
Final Beam Energy (GeV)
250
20161201 K.Kubo
11
Conclusions
• Performance at 500 GeV c.o.m.
– Low emittance transport simulations have been performed
using the latest ILC Lattice decks, emittance growth within
budgets
• BBA performance for Z-calibration run has been assessed:
– Coasting beam (performs better)
– Reduced gradient
Optics must be rematched
• Emittance of the beam spent for positron generation
degraded, to be checked if this is OK
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