Observations on ILC LET and Ground Motion

1
Observations on ILC LET and Ground Motion

• Paul Lebrun
• Fermilab CD/AMR

2
Overview

• Brief description of Low Emittance Transport
  (LET) work
• First look at Ground Motion,
• Data vs ATL model
• In CHEF, for a 5 to 50 GeV, ILC-style LINAC
• Future work
• More realistic alignment
• Ground Motion
• Modify, improve ATL ass need be
• More data ! Longer distances, higher frequency..
  

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LET Far from final

• Overview of progress of LET at Fermilab.
• Simulation work Done in TD, CD, AD
• AD/CD
• CHEF Accelerator Simulation code, maintained by
  Francois Ostiguy (AD) and Leo Michellotti (CD)
• Alex Valishev Main Linac Lattice and LET
  studies.
• TD Working with LIAR and Lucretia (Kirti
  Ranjan),
• CD Valentin Ivanov, P.Lebrun, LET, static and
  dynamic, using private code and CHEF.
• Dynamical LET
• High on priority list.. With CHEF, just started a
  few weeks ago.
• Somewhat software intensive (GM code, vibrations,
  beam jitter..)
• CPU intensive!!

4
LET The basics

• Something we already do for RunII, in the TeV!
• Re-adjusting orbits to preserve emittance.
• 2D Vertical phase space for ILC is 50 times
  smaller then our few pi numbers..
• ILC is pulsed machine, not a relatively stable
  ring
• No orbit, just a trajectory.
• Linacs
• Dispersion (D) Free Steering( DFS) method.
• Given large uncertainties on BPM offsets, tune
  the dipole correctors to a given Dispersion
  function instead of a prescribed path. If so,
  the BPM offsets cancel out.
• If D is small or, preferably, set to zero, BPM
  scale error also dont matter.

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LET Benchmarks And Algorithms

• While the DFS method is in principle
  straightforward, there are numerous tricks to
  play to make it more realistic, and to optimize
  it in case of multiple sources of Dispersion.
• Implementation often messy.
• LET performance may depend on the quality of
  tracking code ? Benchmark.
• An agreed upon lattice (Tesla Main Linac)
• BPM resolution
• Wakefield
• Misalignments and BPM offsets.
• . (That was the hard part!)

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Benchmark, Fixed dipole setting

Non trivial emit emittance growth! Ups and down
because D taken out.. and coming back..
Agreement not perfect, sensitivity to small
local difference in tracking.. Improves if
Dispersion if corrected.
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Determining Dipole Settings..

O.K. Performance agreement is o.k., but solutions
are different
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What does it has to do with GM ?

• If multiple solutions to a given misalignment
  pattern give roughly the same performance, are
  these solution robust and stable.
• Preliminary results on the dynamical problem
  (initial set of misalignment, with beam jitter
  and ground motion) show that we are not able to
  converge towards a solution that has good
  performance, over time.
• So more work is needed!

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Ground Motion Model and reality.

• Valentin Ivanov translated in C the ATL model
  from A Seryi.
• Integrated in CHEF
• First order, naïve comparison with Jim Volk et al
  data.
• For October only.. No long time duration studies!
• From the MINOS hall.. Not the good Galena
  Platteville dolomite.

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From Jims web site..

Big long term motion! 20 microns swing is very,
very likely to demand a complete retuning
(i..e,DFS) re-adjusting of the LINAC. 500
microns is also likely to justify a physical
re-alignment. Lots of frequencies..
L2 (microns)
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Yes, we see the moon tides

Data taken starting Oct 12, 2008 The 12
hours periods seems to be there, visible for
about 2 days. 0.25 to 0.5 microns/hour. Then
the tide amplitude rises and long term (week)
motion also increases..

L2 (microns)
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Data conversion taking out the global tilt

Delta 2/3_1 L2 (L3 L1)/2. Large
fluctuations remains.. 40 microns, over a few
days, over 60 meters..
13
Comparison with ATL, for 2 hours.

Oct 8, 1004 A.M. Oct 3 400 A.M.
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Why two hours ?

• At best, a complete DFS re-steering will take
• 20 pulses per setting, to average over beam
  jitter and finite BPM resolution.
• x2, need off/On momentum to measure Dispersion.
• 20 iterations per local DFS section.
• x 30 to 60 the number of DFS section for the
  entire LINAC.
• 80 uptime
• gt 1 to 3 hours

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LET Perf. with Beam Jitter GM

Very preliminary..
Vertical Emittance, not corrected for Dispersion,
for
Emittance, corrected for Dispersion.
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Will it work ?

• With only magnetic steering ?
• At first try, DFS steering did converged,
  albeit with looser a convergence criteria then in
  the static case. Yet, the emittance growth is
  large 40 of the budget in 2 km !
• And I ran for 10 minutes.. (one day of CPU
  time!)
• Need to run for longer periods
• More realistic misalignements!!!!
• Things to try (Software)
• Concurrent DFS steering across sections ?
• Better DFS steering algorithms and parameters
• Further check of Ground Motions..
• Better Control software (??)

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Further investigations...

• Movers on quadrupoles and/or cavity ?
• Cavity tilts at 10 GeV have really bad effects
  on LET !!
• Much smaller (lt 1 nm. Rad) are predicted if the
  cavities can be placed laser straight, one only
  has to correct for quadrupole displacements.
• Feed forward Steering..Laser-track the motion of
  the machine, and use Beam steering to check..
  
• Need a lot more instrumentation !
• HOM BPM
• Synch. Rad. detectors ?

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Better ground Motion Modeling ?

• Conversion of exiting data to formal ATL
  parameters
• Beyond minimal ATL
• Understanding why drives these motions?
• Tide related frequencies/phases well known!
• Needed if feed-forward will be considered.
• However, evidently, earth quakes are notoriously
  hard to predict!

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Better Ground Motion Data?

• Goal improve ATL model, make it reliable.
• Systematic error analysis on existing HLS data.
• Frequency Need 5 Hz
• 10 Hz probably..
• Not KHz (intra-train effect something entirely
  different. Probably not ground motion!)
• Means Laser-tracker technology.
• Longer distance..
• MINOS or Aurora mine ? Or other site ?