450 GeV Preliminary Commissioning: Measurement Programme

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450 GeV Preliminary Commissioning Measurement
Programme

• polarities
• apertures
• basic optics checks

thanks to Rhodri Jones, Stefano Redaelli,
Ralph Steinhagen
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additional aims on LHC-commissioning web page
https//lhc-commissioning.web.cern.ch/lhc-commiss
ioning/

• measurement program with pilots
• low intensity, polarities aperture (1st pass)
• linear optics checks
• trajectory vs. kick, phase advance,
• BPM corrector polarity, dispersion
• tunes, orbit, chromaticity, coupling

time estimate (lhc-commissioning web) 4 days per
ring ? 8 days with beam in total
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flow chart from Mike Lamont
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from lhc-commissioning web site
Q
? coupling correction 1st pass
Q
orbit
corrector BPM polarity
linear optics check
? coupling correction 2nd pass
aperture scan
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expected static errors
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BPM resolution

• Nominal resolution (5 µm) for
• single bunch intensity gt 2-3x1010 charges per
  bunch
• global orbit 43 pilot bunches

E.B. Holzer, J.-J. Gras, O.R. Jones, Chamonix XV
workshop
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initial adjustments

• set tunes to nominal or alternative WP
• (0.28/0.31) or (0.285/0.385)
• nominal WP requires coupling correction
• - from tune response to two orthogonal skew-quad
  families
• - or using multi-turn BPM readings
• if we use alternative WP need to switch later
• correct chromaticity
• - maximize decoherence time (fast)
• - radial steering
• smoothen orbit IR3, IR7 (cleaning), IR6 (dump)
  and injection region critical

S. Fartoukh, LCC 23/10/2002
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tune measurement raw data
Q50
Q-50
x
turns
Q20
Q2
HEADTAIL, coupling k0.05, broadband impedance,
detuning w. ampl., space charge, Nb 3x1010
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tune measurement spectrum
Q50
Q-50
Q20
Q2
peak yields same tune value 0.2813/-0.0003 in
all 4 cases
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BPM corrector polarities

• already partially checked during threading
• (Jorg Wenninger)
• 530 x 2 orbit correctors per ring excite each to
  Dx,y 500 mm (qcor5 mrad ltlt 1.2 mrad (max.))
• 1056 x 2 BPMs per ring
• time required 10-30 s per corrector
• ? estimate 4-9 h per ring for polarity,
  calibration, side-benefit redundant data for
  linear optics check
• in addition
• 3 interlock BPMs in IP6 for MP (bump to check BPM
  position w.r.t. TCDQ)
• BPMs at TDI

Ralph Steinhagen
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what is a bad BPM?

• wrong polarity
• wrong plane
• large noise (spray?)
• wrong location
• nonlinearity?
• large orbit offset?
• calibration error
• other

discussion triggered by Peter Limon Oliver
Bruning in Chamonix_at_Divonne
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basic optics checks

• process orbit-response data from corrector tests
  (5-20 mm resolution) to get b coupling
• take multi-turn BPM data for harmonic analysis
  (50-200 mm resolution, fast) to get f, b
  coupling
• possibly K modulation at a few critical locations
  (wire scanners, SL monitor, IP6,)
• radial steering for measuring dispersion (expect
  few cm or resolution) Q off-momentum b
  (multi-turn BPMs)
• coupling correction
• change of working point?
• estimated minimum time 3-5 h / ring

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finding local sources of b beat

• fit against model / inversion of quadrupole
  response matrix
• e.g., from measured phase beating
• may not be trivial, especially for distributed
  errors
• simultaneous fit of data from both rings

constraints
in short
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Example 1, SPS comparing measurement prediction
phase beating induced by a single quadrupole
QE604 in the SPS red measurement, blue model
prediction (J. Klem, 2000)
from phase of harmonic analysis
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Example 2, SPS result of fit using SVD
pseudo-inversion
SPS test with quadrupole QE603, DQ0.05, varying
weight l for DK in SVD solution
weight low many quadrupoles excited to get
perfect fit
reasonable weight
correct quadrupole is identified for proper
weight l
C. Carli, G. Arduini, F.Z., EPAC04
weight high all quadrupole changes a small
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aperture

• determine global transverse aperture using pairs
  of orthogonal correctors (minimum 8 measurements
  with beam loss, per ring) center beam inside
  aperture for each corrector
• momentum aperture by radial steering until beam
  loss (2 measurements)
• determine center frequency? (radial steering
  sextupoles) important to compare both rings
• in case of problem local closed bumps or sliding
  bumps across IRs or arcs
• estimated minimum time 2-3 hours / ring

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(No Transcript)
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y aperture 14s limited at VMAJI/B in IR2, 3, 7
(8)
x aperture 14s limited at VSSB VMAII/B in
all SSS
apertures for ideal optics
d aperture 0.008 limited at VSSB VMAII/B in
IR2, 3, 7 (8)
from mixture of MAD-X optics database and
aperture model setup for collimation studies
(Stefano Redaelli)
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conclusions

• initial measurements can be done in 8 days (2
  rings)
• readiness of procedures software critical
• up-to-date MAD-X or SIXTRACK model for flight
  simulations?
• measured field errors, apertures, realistic
  relative misalignments (including spool-pieces
  etc.)

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appendix
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apertures for ideal optics role of dispersion
horizontal aperture / total beam size
correlation between xb d aperture
similar to picture of Ax/sx,b on slide 18