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Checks of LBDS for new IR6 optics

Checks of LBDS for new IR6 optics. B.Goddard , with input from C.Bracco, R.Bruce , S.Fartoukh, V.Kain, R.Tomas -Garcia, J.Uythoven. Phase advance MKD to TCDQ/TCSG. Motivation. Present nominal phase advance MKD (kick centre) to TCSG6 is ~94.7 deg

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Checks of LBDS for new IR6 optics

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  1. Checks of LBDS for new IR6 optics B.Goddard, with input from C.Bracco, R.Bruce, S.Fartoukh, V.Kain, R.Tomas-Garcia, J.Uythoven

  2. Phase advance MKD to TCDQ/TCSG

  3. Motivation • Present nominal phase advance MKD (kick centre) to TCSG6 is ~94.7 deg • Idea from S.Fartoukh during discussions on ATS to rematch IR6 to exactly 90 deg. • Improves protection in terms of amount of beam transmitted above a certain amplitude. • Effective gain depends on particle amplitude from the bunch core (with 2 um ex and 8.5 sigma tight setting, gain 0.2 s for 3 s particles, 0.03 s for on-axis)  small but useful

  4. Considerations for dump system • Possible gains • Trajectories and apertures in dump region • Beta functions in TD lines • Operational limits of TDE, VDWB, BCTDD, TCDQ, TCDS • Setting-up of TCSG/TCDQ • Asynchronous dumps and TCTs • Measured values • Extra checks and commissioning time needed

  5. Gains • Gain about 0.2 sigma for particles with 3 (real) sigma amplitudes (for 2 um emittance) • Could reduce margins needed from TCSG/TCDQ to TCT, to shadow TCTs

  6. Trajectories and apertures in dump channel • Strengths of Q4 L6 for B1 and R6 for B2 are unchanged • Trajectories identical to nominal • Changes in beta functions in extraction region • 8% larger at TCDS – 4% larger beam size (1.096  1.140 mm) • N1 already at 6.5 – would be reduced to about 6.25 at TCDS entrance • 16.3 mm aperture – lose 0.55 nominal sigma here in H plane. • 14% smaller at TCDQ – 7% smaller beam size • Beam size 3% larger at MSDA1, 2.5% smaller at MSDC15 • Protection by TCDS OK (up to 17% change in betas) • No major issues for trajectory or local aperture • Only question is about n1 = 6.25 at TCDS, at 450 GeV (calculated for 3.75 um beams).

  7. Beta functions in TD lines • No change to vertical beta functions • Smaller H values for both beams at TDE (5000  4300 m) • No aperture issues • Reduction in beam sigma from 1.59 to 1.47 mm ( 7 TeV) • Increased p+ density on VDWB, BTVDD, TDE

  8. Optics functions in TD lines B1 nominal optics

  9. B1 90.0 deg

  10. B2 nominal optics

  11. B2 90.0 deg

  12. Operational limits: TDE/VDWB/BTVDD • Regularly solicited (each fill) • Designed for ultimate beam intensity (2808b of 1.7e11 p+ at 7 TeV with 3.75 um exy) • Assuming (pessimistic) that limit scales with peak energy density, for constant by have as safe limit (25 ns)

  13. Scaling of limit intensities: TDE/VBWD, BTVDD • New optics reduces ‘safe’ intensity limits by ~0.1e11 • Not an issue for 50 ns • Main effect from emittance much lower than nominal

  14. TCDS, TCDQ operational limits • Only asynchronous dumps of which one for 3.5 TeV 2010-11, with 1 pilot (expected to be worse for 7 TeV...) • 47 bunches on TCDS, 34 bunches on TCDQ (depending on failure) • TCDS beta function is larger with the new optics • Situation is slightly better – more margin • TCDQ beta function is 14% smaller • 7% smaller beam size may have an impact on the TCDQ performance limit for small emittance • TCDQ anyway not OK for full intensity beam - being redesigned now (for LS1) • Needs detailed FLUKA and thermomechanical simulations for each case - very time consuming... • Plan sensitivity analysis to beam size in present TCDQ upgrade study • Present situation already not comfortable) – new optics will make this slightly worse – difficult to quantify as present limits unknown

  15. Setting up of TCSG/TCDQ • 7% smaller beam size for given emittance; will reduce slightly the accuracy (in terms of sigma/setting up step) • Not expected to be a problem

  16. Asynchronous dumps • Phase advances MKD to TCTs with the new IR6 optics hardly change at all (max 0.2 deg) |sin(q)| |sin(q)|

  17. Measured values • Rogelio has checked measurements made at 3.5 TeV with 1m_10m_1m_3m (with 1.5 m b* corrections in), and calculated MKD-TCSG phase advance • B1: essentially no difference to nominal (0.001) within the error of the measurement (±0.001) • B2: measure 0.254 ±0.001, compared to nominal 0.263. • For B2 correction of phase by -0.013 would make things worse, if the beta-beating remains unchanged • Expect new beta-beating pattern for new b* and new energy • Correct strategy would be to deploy new ‘90 deg’ optics and then constrain beta-beat correction to conserve this phase advance in IR6... • Also note: may have much larger loss of protection (0.5 s) from beam size variation at TDDQ/TCSG and TCTs – should use measured betas for calculating settings of these devices!

  18. Extra setting up and checks for 2012 startup, if new IR6 optics? • No changes to Q4, MKD, MSD strength – LBDS energy tracking does not need extra checks • Will anyway need to carry out substantial range of LBDS checks • TCDQ setup, interlock BPM setup and checks, dump sweeps • Should foresee extra aperture checks in IR6 at TCDS, Q4/5 • Maybe few hours per beam at 450 GeV • New TCSG/TCDQ settings – probably anyway the case • Maybe some more time for beta-beat corrections • Realistically, maybe 1-2 shifts for ‘extra’ tests

  19. Summary New optics can reduce transmission amplitudes into LHC by 0.03 - 0.20 sigma, for 0 to 3 sigma particle amplitudes respectively (with 2 um emittance). Trajectories in dump channel unchanged Lose about 0.5 sigma at TCDS entrance: n1 reduced to 6.25 at injection. Slightly smaller beam size on dump block: sticking to design p+ density means reduce intensity ‘reach’ by 0.1e11, for any given emittance. Slightly better for TCDS (larger beam), but slightly worse for TCDQ, with 7% smaller beam, already known to be potential limit… Setting up accuracy/speed should not be affected Phase advances to TCTHs basically unchanged: no issues for asynch dumps 2011 phase advances: B1 = 0.263, B2 = 0.25. New beta-beat expected in 2012, but will need to include in correction strategy, after measurement. Extra testing and validation maybe 1, maximum 2 shifts

  20. Conclusion • No major issues identified • Potential gain is real but small • Risk making things worse unless included in b-beat correction strategy • Some unknowns, especially TCDQ robustness • Goes in wrong direction • Already not OK for nominal beam at 3.5 TeV • Propose to keep new optics “in pocket” for future (>LS1), especially when approaching nominal settings at 6.5-7.0 TeV • Use 2012-13 to investigate key points, especially TCDQ robustness (include in new design study), TDE limits as function of sigma, correction of beta-beat to nominal, ... • In any case beta-beat correction and collimator setting definition need to take account of these issues

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