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Transfer Function for Separation Dipoles

Transfer Function for Separation Dipoles. Frank Zimmermann LHCCWG 12.07.2006. Discussions with O. Bruning, S. Fartoukh, M. Giovannozzi. the problem. D1-D2 transfer function errors can have a significant effect on closed orbit during squeeze (10 units → 3 s orbit change at triplet)

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Transfer Function for Separation Dipoles

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  1. Transfer Function for Separation Dipoles Frank Zimmermann LHCCWG 12.07.2006 Discussions with O. Bruning, S. Fartoukh, M. Giovannozzi

  2. the problem D1-D2 transfer function errors can have a significant effect on closed orbit during squeeze (10 units → 3s orbit change at triplet) local correction requires careful analysis and distinction between • D1/D2 transfer function errors • Triplet alignment errors • Triplet gradient errors with crossing-angle bump offsets [O. Bruning, Chamonix XII]

  3. IR1 layout D2 D2 D1 D1 separate BPM common BPMs separate BPM BPM distances to IP: 21.35, 31.53, 58.32, 151.14 m

  4. original procedure • triplet alignment optics with low-b quads off to define straight line with 6 or 8 BPMs; • k-modulation of individual Q1, Q2 or Q3 magnets to find offsets w.r.t. to reference line from BPMs • differences in the lines for beam1 and beam2 indicates D1/D2 transfer line error • after correcting D1/D2 powering error obtain reference line for triplet alignment [O. Bruning, Chamonix XII]

  5. LHC triplet alignment optics [A. Verdier, LHC PN 325, 2003] requires about half the nominal emittance for aperture reasons; x&y tunes lower by 1 unit, if IR1 & 5 both use this optics

  6. “refined” procedure (?) • correct incoming beam upstream of D2 for zero offset and angle • adjust D1 on one side to steer beam on 0-slope trajectory through the IP • then look at other side • and/or adjust D1 and D2 together to get both beams on the same orbit? S. Fartoukh, M. Giovannozzi, F.Z.

  7. problems • low-b quads: misalignment of mechanical & magnetic axes 0.1-0.2 mm in x, 0.5 mm in y; beam needs to be steered through the mechanical center! • BPM offsets may cause error of up to 5 mrad (?), compared with total deflection angle of 1.5 mrad; this is larger than desired precision of 3x10-4 • BPMs might have different offsets for beam1 and beam2 (?) S. Fartoukh, M. Giovannozzi, F.Z.

  8. questions • in which aspect is the D1/D2 transfer function effect any different from other closed-orbit errors of the two beams, and why does it need to be treated differently? • do we want to measure transfer functions with beam at 450 GeV and at 7 TeV? • do we want to use alignment optics?; if yes, with which beam and which BPM resolution?

  9. I propose following procedure • alignment optics at injection to define straight reference line for both beams (BPM readings) • K-modulation to measure quad misalignments and align where necessary • apply 2-beam orbit correction across IR region; include D1 and D2 as additional correctors

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