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 05.04.2006

“additional aims” on LHC-commissioning web page https://lhc-commissioning.web.cern.ch/lhc-commissioning/ 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 05.04.2006

flow chart from Mike Lamont Frank Zimmermann, Initial Measurement Program at 450 GeV, LHCCWG 05.04.2006

from lhc-commissioning web site Q ← 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 05.04.2006

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 05.04.2006

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 05.04.2006

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 05.04.2006

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 05.04.2006

tune measurement – spectrum Q’=50 Q’=-50 Q’=20 Q’=2 peak yields same tune value 0.2813+/-0.0003 in all 4 cases Frank Zimmermann, Initial Measurement Program at 450 GeV, LHCCWG 05.04.2006

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 05.04.2006

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@Divonne Frank Zimmermann, Initial Measurement Program at 450 GeV, LHCCWG 05.04.2006

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

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 05.04.2006

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 05.04.2006

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 05.04.2006

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 05.04.2006

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

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 05.04.2006

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 05.04.2006

appendix Frank Zimmermann, Initial Measurement Program at 450 GeV, LHCCWG 05.04.2006

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 05.04.2006