1. 450 GeV Preliminary Commissioning: Measurement Programme
polarities
apertures
basic optics checks
thanks to Rhodri Jones, Stefano Redaelli,
Ralph Steinhagen
Frank Zimmermann, Initial Measurement Program at 450 GeV, LHCCWG

2. “additional aims” on LHC-commissioning web page
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
Frank Zimmermann, Initial Measurement Program at 450 GeV, LHCCWG

3. flow chart from Mike Lamont
Frank Zimmermann, Initial Measurement Program at 450 GeV, LHCCWG

4. from lhc-commissioning web siteQ
← coupling correction 1st pass Q’
orbit
corrector & BPM polarity
linear optics check
← coupling correction 2nd pass
aperture scan
Frank Zimmermann, Initial Measurement Program at 450 GeV, LHCCWG

5. expected static errors
parameter
error
origin
tune
<0.4
quad errors, dipole field, x-orbit
coupling
<0.2
from a2, quad rolls, y-orbit at sx
off-momentum (d=2x10-3) beta beat
< 21%
quad errors, orbit at sext’s
chromaticity Q’
< 320 b3
Frank Zimmermann, Initial Measurement Program at 450 GeV, LHCCWG

6. BPM resolution Nominal resolution (5 μm) for
single bunch: intensity > 2-3x1010 charges per bunch
global orbit: 43 pilot bunches
E.B. Holzer,
J.-J. Gras,
O.R. Jones,
Chamonix XV
workshop
Resolution (rms)
Pilot bunch
Trajectory (single shot)
200 μm
Orbit (224 turn average)
20 μm
Nominal intensity bunch
Trajectory (single shot, single bunch)
50 μm
Trajectory (average of all bunches)
5 μm
Orbit (average of all bunches over 224 turns)
Frank Zimmermann, Initial Measurement Program at 450 GeV, LHCCWG

7. initial adjustments set tunes to nominal or alternative WP
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
Frank Zimmermann, Initial Measurement Program at 450 GeV, LHCCWG

8. tune measurement – raw data
Q’=50
Q’=-50 x
turns
Q’=20
Q’=2
HEADTAIL, coupling k~0.05, broadband impedance, detuning w. ampl., space charge, Nb= 3x1010
Frank Zimmermann, Initial Measurement Program at 450 GeV, LHCCWG

9. tune measurement – spectrum
Q’=50
Q’=-50
Q’=20
Q’=2
peak yields same tune value / in all 4 cases
Frank Zimmermann, Initial Measurement Program at 450 GeV, LHCCWG

10. BPM & corrector polarities
already partially checked during threading
(Jorg Wenninger)
530 x 2 orbit correctors per ring; excite each to Dx,y +500 mm (qcor~5 mrad << 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
Frank Zimmermann, Initial Measurement Program at 450 GeV, LHCCWG

11. 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
Frank Zimmermann, Initial Measurement Program at 450 GeV, LHCCWG

12. 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 ( 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
Frank Zimmermann, Initial Measurement Program at 450 GeV, LHCCWG

13. 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
in short
+ constraints
Frank Zimmermann, Initial Measurement Program at 450 GeV, LHCCWG

14. 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
Frank Zimmermann, Initial Measurement Program at 450 GeV, LHCCWG

15. Example 2, SPS: result of fit using SVD pseudo-inversion
SPS test with quadrupole QE603, DQ~0.05, 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
Frank Zimmermann, Initial Measurement Program at 450 GeV, LHCCWG

16. 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
Frank Zimmermann, Initial Measurement Program at 450 GeV, LHCCWG

17. Frank Zimmermann, Initial Measurement Program at 450 GeV, LHCCWG 05.04.2006

18. y aperture ~14s x aperture ~14s limited at VMAJI/B limited at VSSB
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)
Frank Zimmermann, Initial Measurement Program at 450 GeV, LHCCWG

19. 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.)
Frank Zimmermann, Initial Measurement Program at 450 GeV, LHCCWG

20. appendix
Frank Zimmermann, Initial Measurement Program at 450 GeV, LHCCWG

21. 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
Frank Zimmermann, Initial Measurement Program at 450 GeV, LHCCWG