ILC Feedback Simulations

1
ILC Feedback Simulations

• (5-Hz)
• Linda Hendrickson
• rev Oct 13, 2005

2
5-Hz Integrated Feedback Simulations

• Linac feedback distribution 5 distributed loops
  per beam, each with 4 horizontal and 4 vertical
  dipole correctors, and 8 BPMs (XY). Based on SLC
  experience and NLC simulations by LJH.
• BDS feedback distribution 1 BDS loop per beam,
  9 BPMs and 9 dipole correctors, both horizontal
  and vertical. Based on NLC simulations by Seryi.
• Linac and BDS feedbacks Cascaded system of 6
  loops per beam loops dont overcompensate beam
  perturbations, but can be independently disabled
  for operational convenience. SLC-style single
  cascade (each loop communicates beam information
  to single adjacent downstream loop).
• Linac and BDS loops have exponential response of
  36 5-Hz pulses.
• IP deflection (XY), not cascaded,
  exponential 6 pulses (like SLC).
• Matlab/liar/dimad/guinea-pig platform. Upgraded
  liar/dimad for energy and current jitter, and
  dispersion measurements.
• KEK-model ground motion (noisy site). Study
  effects of component jitter, energy, current,
  kicker jitter. Problems BDS beamsize very
  sensitive using dispersion compensation and
  perfect energy measurement.

3
Feedback Simulations
BPM readings in linac after 30 minutes ground
motion
IP loop
5 distributed linac loops
1 BDS loop
Emittance growth in linac 100 after 30 min
KEK ground motion jitter for 10 seeds, 6
with feedback (3 with feedback without jitter).
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Beamsize growth effects, with feedback
Single-beam studies of beamsize growth, with 5-hz
feedback in LINAC and BDS. Perfect initially,
add 30 minutes KEK ground motion, let feedback
converge -gt 5 beamsize growth. Increase energy
spread for undulator (.15 end of linac this
effect needs more study!) -gt 14. Add component
jitter (25 nm BDS, 50 nm linac) -gt 15. Add 5-Hz
KEK ground motion -gt 18. Add kicker jitter
(.1 sigma), current jitter (5), energy jitter
(.5 uncorrelated amplitude on each klystron, 2
degrees uncorrelated phase on each klystron, 0.5
degrees correlated phase on all klystrons, BPM
resolution .1 um. -gt 21
(Note results are with respect to design
beamsizes, which vary slightly with of
particles in guinea pig).
Undulator
5 Hz ground.
30 min ground.
Kicker, current, energy jitter, BPM resol.
Component jitter
5
Beamsize growth effects, with feedback
Beamsize growth for electron beam, at various
marker points from end-of-linac through the IP.
The following results are for 30 minutes K ground
motion, with 5 Hz jitter, electron beam with
undulator energy spread, no other jitter sources.
(Note results are with respect to simulation
beamsizes, which vary slightly with of
particles in guinea pig).
Avg of beamsize, as fraction of original
beamsize X Y X angle
Y angle 1 1.0167 1
1.016 1.0001 1.0164 1.0001
1.0176 0.99998 1.0151 1.0001
1.0248 1.0001 1.0509 1.0002
1.0266 0.99838 1.0247 0.99507
1.0215 1.0003 1.0185 1.0003
1.0184 1.0003 1.0186 1.0005
1.0185 0.99918 1.0185 0.99845
1.0186 1.0025 1.0185 1.0037
1.0229 0.99957 1.224 1.0026 1.0185
end of linac
ST4
IP
6
Beamsize growth effects, with feedback
Beamsize growth for electron beam, at various
marker points from end-of-linac through the IP.
The following results are for 30 minutes K ground
motion, with 5 Hz jitter, electron beam with
undulator energy spread, with all other jitter
sources, including component, kicker, current,
energy jitter.
Avg of beamsize, as fraction of original
beamsize X Y X angle
Y angle 1.0009 1.0236 0.99937
1.0245 1.0009 1.0247 1.0004
1.0258 1.0014 1.0238 1.0001
1.0337 1.0016 1.0579 1.0001
1.0354 1.0012 1.0339 0.99815
1.0309 1.0003 1.0288 1.0007
1.0297 1.0005 1.0283 1.0001
1.0301 0.9995 1.029 1.002 1.0271 1.0041
1.0277 0.99835 1.0664 1.0003 1.2423
1.0042 1.0284
end of linac
ST4
IP
7
Beamsize growth effects, with feedback
Beamsize growth for POSITRON beam, at various
marker points from end-of-linac through the IP.
The following for 30 minutes K ground motion,
with 5 Hz jitter, electron beam without extra
undulator energy spread, with all other jitter
sources, including component, kicker, current,
energy jitter.
Avg of beamsize, as fraction of original
beamsize X Y X angle
Y angle 1.0035 1.0037 0.99659
1.0096 1.0016 1.0068 0.99491
1.0097 1.0008 0.99964 0.99958
1.01 1.0008 1.004 0.99956 1.0102 1.0073
1.0102 0.99956 1.0094 0.99974 1.009
1 1.01 0.99988 1.0085
0.99905 1.0103 0.99984 1.0092 1.003
1.0074 1.0021 1.008 0.99414
1.0479 0.99998 1.0743 1.0022 1.0086
end of linac
ST4
IP
8
Beam Jitter in Feedback Simulations
Jitter in the linac, as a fraction of beamsize.
Plots are for a single seed, simulations with all
jitter sources included.
Y jitter vs z along linac
X jitter vs z along linac
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Beam Jitter in Feedback Simulations
For 10 seeds, move the ground 30 minutes with
model K, apply ground motion and sample for 200
pulses while feedback converges. The following
are average beam jitter as a ratio of perfect
simulated beamsize, for the last 20 pulses,
after feedback has converged.
All Jitter Sources
5 Hz ground only
End Linac e- average X 0.032 Y 0.70
X 0.016 Y 0.33 IP e- average
X 0.28 Y 12.5 X 0.12
Y 3.4 IP avg 2beam diff X 0.33
Y 15.8 X 0.17 Y 3.7 IP
maximum 2beam X 1.57 Y 49.0
X 0.72 Y 15.9 difference
(777 nm) (197 nm)
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Beam Jitter in Feedback Simulations
Move the ground 30 minutes with model K, apply
ground motion and all other jitter sources, and
sample for 200 pulses while feedback converges.
The following shows the vertical beam position at
the interaction point for both electrons and
positrons, for a single seed.
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2-beam Integrated Feedback Simulations
2 beams, 5-Hz linac, BDS and IP deflection
feedback. Perfect initially, feedback turned on
after 30 minutes of KEK ground motion. 5 Hz
ground motion, added component jitter, kicker,
energy, current jitter. No angle feedback, no
intratrain feedback. For the first 20 seconds,
IP feedback cannot keep up with large BDS
steering changes. After 20 seconds, beams kept in
collision but luminosity is poor (17 in
preliminary simulations, 71 with perfect
intratrain IP feedback).
Beam-size jitter in steady-state.
Beam sizes decrease after feedback is turned on.
(Note seed-dependent beamsize from ground motion
in this seed, e- becomes smaller).