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LHC Closed Orbit for Beam 2 - December 2008

This report discusses the closed orbit of Beam 2 in the LHC, addressing convergence issues, misalignment, and orbit corrections. The results indicate good performance and the potential for achieving a very good orbit RMS in both planes.

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LHC Closed Orbit for Beam 2 - December 2008

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  1. LHC Closed Orbit For Beam 2 J. Wenninger December 2008

  2. Closed Orbit Sector by sector dp/p offsets • RMS : 1.6 mm H, 1.3 mm V – with little effort !!! • Vertical bare orbit converged well. • Need to be careful when correcting orbits with large initial rms : convergence issues to the non-linearities • >> send in steps (~20% of full correction). • LHC fRF,cap,LHC = 400'788'963 Hz • LHC ‘Theoretical fRF,nom-LHC = 400'788‘734 Hz • Average energy offset of CO : -0.094% = -9.4 units.

  3. Horizontal Orbit 12th Sept 08 • Corrector RMS 10 mrad – with MICADO

  4. Vertical Orbit 12th Sept 08 • Corrector RMS 8.6 mrad – with MICADO

  5. Bare Orbits • Bare orbits after [linear] unfolding of all corrector kicks. • Similar quality H & V : 12 mm rms H, 11 mm rms in V – peaks ~ 30 mm

  6. Alignment • The bare orbit rms is related to the misalignment through an optics sensitivity factor k : • RMSorbit = k RMSalignment R. Steinhagen, S. Redaelli, J. Wenninger, CERN-AB-2005-087 An estimate for the rms alignment error is therefore given by rms orbit/30 = 0.36 (V) to 0.4 (H) mm

  7. ‘Ultimate’ Correction - H • Corrected orbit with SVD 240 eigenvalues (~ limit) • H rms value dominated by dp/p offset, rms 0.52 mm without dp/p contribution. • No excessive kick (but some ‘larger’ kicks around IR6 and IR8). • Typical max. kick @ 7 TeV is ~ 80 mrad.

  8. ‘Ultimate’ Correction - V • Corrected orbit with SVD 240 eigenvalues (~ limit). • V rms value down to 0.35 mm(rejecting some more or less obvious outliers). • Max offset of ‘good’ (green) BPMs is +-1 mm ! • The corrector settings reflect the systematic V offsets in S23, S34 and S45. • No excessive kick (but some ‘larger’ kicks around IR2). • Typical max. kick @ 7 TeV is ~ 80 mrad.

  9. Conclusions • The BPM system performance was great (at least for this stage). • Orbit corrections worked well and converged : optics ‘reasonable’. • Bare orbits indicate good alignment of ~0.35 to 0.4 mm. • We have to understand the funny vertical offsets in sectors 23, 34, and 45. Can be partly, but apparently not fully, explained by BPM offsets. • We can potentially achieve a very good orbit rms (<< 1 mm) in both planes with reasonable kick strengths : could can 1-2 sigma of aperture at 450 GeV !

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