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MAIN ISSUES IN THE MAGNETIC FIELD MODEL FOR THE SECOND HALF OF 2010

CERN, 22 th June 2010 FiDeL meeting. MAIN ISSUES IN THE MAGNETIC FIELD MODEL FOR THE SECOND HALF OF 2010. E. Todesco CERN, Geneva, Switzerland With inputs from L. Deniau, P. Hagen, R. Steinhagen, R. Tomas,. OUTLINE OF Commissioning conditions. Precycling strategy

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MAIN ISSUES IN THE MAGNETIC FIELD MODEL FOR THE SECOND HALF OF 2010

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  1. CERN, 22th June 2010 FiDeL meeting MAIN ISSUES IN THE MAGNETIC FIELD MODEL FOR THE SECOND HALF OF 2010 E. Todesco CERN, Geneva, Switzerland With inputs from L. Deniau, P. Hagen, R. Steinhagen, R. Tomas,

  2. OUTLINE OF Commissioning conditions • Precycling strategy • Using previous run as precycle if not abnormally terminated • « Fast » precycle for circuits that fell down • 2010 • Probably going to 10 A/s soon, now at 2 A/s • For the moment no squeeze below 3.5 m, but 2 m will come

  3. CHROMATICITY DRIFT DURING RAMP: critical • Chromaticity drift during ramp • About 15 units (0.3 units of b3) - too large – rather systematic • Correction strategy [R. Steinhagen] • Linear correction from injection to ramp of the systematic shift of DQ=12 • b3 spool piece correction has been raised from 0.1 (as expected at 2 A/s) to 0.5 (as should be at 10 A/s) – not justified and to be understood • Beam measurements of b3 decay? Drift of the chroma during ramp after linear correction [R. Steinhagen] Drift of the chroma during ramp, no corrections [R. Steinhagen]

  4. CHROMATICITY DRIFT DURING RAMP: critical • Activities from the side of magnetic measurements • Measure at 2 A/s [L. Walckiers, L. Fiscarelli, G. Montenero, in progress] • Review the data postprocessing [L. Deniau, in progress] • Additional corrections (10%) could be expected New postprocessing of decay data in the main dipoles [L. Deniau]

  5. BETA BEATING - injection • Beta beating was the main critical issue at the beginning of 2010 • A lot of work has been done on both sides (beam measurements and magnet measurements) • Started with about 50% at injection • Evidence of large corrections (3%) in MQWA (R. Tomas) • Very low currents in MQWB – large errors • Wrong precycling found [P. Hagen] • After this correction went down to 1.5% • MQWB got worse • New measurements and improved model (P. Hagen) • We now run without corrections at injection • For the future, one could try to further improve

  6. BETA BEATING - Squeeze • Beta beating during squeeze • At b*=3.5 m beta beating is tolerable but could be improved – main source is IP8 • At b*=2 m beta beating large error in IP8 – cured by 5% change in Q5, but source could be the triplet • Solution is not unique – 5% error in only one Q5 is not physical • Used correction was 10-20 units in the triplet – hard to make a better model • Additional beam measurements will be done • No magnetic measurements are planned • Unfortunately we cannot measure the triplet

  7. CHROMATICITY REPRODUCIBILITY • Reproducibility from run to run to be analysed [N. Aquilina, in progress] • Main contributors: b3 in dipoles, spool pieces, lattice sextupoles, quads plus feed down ? • Correlation between precycling and bare tunes ? • To be expected

  8. TUNE REPRODUCIBILITY: not critical • At 450 GeV tune of the bare machine agrees within ~0.1 from nominal (59.28, 64.31) 0.1/60 ~0.16% • This implies a 0.1% error on absolute knowledge of B2, B1 • Correlation between precycling and bare tunes ? • Not to be expected, but it should be checked[N. Aquilina, in progress] Reconstructed tune of the bare machine in 13 ramps, 2009 and 2010

  9. TUNE DRIFT DURING RAMP: not critical • Tune drift during ramp (cured by feed back): • Less than 0.02 in positive diagonal (Qx, Qy) – tracking of main dipoles and quads is very good – nothing to investigate • About 0.05 in negative diagonal (Qx, -Qy) • Origins: feed-down ? Other quads ? • Could become critical for 7 TeV ramp Drift of the tune during ramp at 1.2 TeV, 7 ramps in 2009-10, and at 3.5 TeV, 6 ramps in 2010

  10. THE “FALLING” ORBIT: not critical • Strange pattern in the used strength of vertical orbit correctors • Systematic offset in 3 sectors of about 1-2 mm – not understood • Equivalent to having a 1 mrad tilt in the main dipoles (spec 0.3 mrad) • More statistics on the runs (Hagen&Hagen, in progress) – analysis of possible causes Used strength in vertical orbit correctors on April 1st at 18h16m

  11. CONCLUSIONS • Critical issues • Chromaticityduringramp • Sources, correction of snapback, variation withprecycles • Beta beating • Fine at injection, reasonableat 3.5 m, to becorrectedat 2 m • A lot of progress !! • The 2 A/s and the 10 A/s precycle • Differences in settings ? • Things to beunderstood but not critical for the moment • Couldbecome relevant for future operation • The large drift of tune duringramp: origins ? • Tune and chroma reproducibilityat injection • The fallingorbit in a few sectors • Tune and chroma drift during squeeze

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