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LHC at 7 TeV/c: comparison phase 1 / IR3MBC

LHC at 7 TeV/c: comparison phase 1 / IR3MBC. N. Mounet, B. Salvant and E. M étral. First comparison between phase 1 and IR3MBC (combined momentum and betatron cleaning in IR3 – settings from A. Rossi) !! Preliminary results !! (some effects, such as temperature, not taken into account).

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LHC at 7 TeV/c: comparison phase 1 / IR3MBC

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  1. LHC at 7 TeV/c: comparison phase 1 / IR3MBC N. Mounet, B. Salvant and E. Métral First comparison between phase 1 and IR3MBC (combined momentum and betatron cleaning in IR3 – settings from A. Rossi) !! Preliminary results !! (some effects, such as temperature, not taken into account)

  2. Reminders: Coupled-bunch modes from all the machine elements in the model (Collimators + MBWs/MQWs magnets + beam screens + warm pipe + broad band) – from dipolar impedance Better in horizontal, but…

  3. Reminders: Coupled-bunch modes from all the machine elements in the model (Collimators + MBWs/MQWs magnets + beam screens + warm pipe + broad band) – from dipolar impedance … worse in vertical. BUT this is supposed to be damped by transverse feedback. Now, is the real part of the tune shift an issue (for transverse mode coupling instability - TMCI - threshold) ?

  4. Vertical coupled-bunch modes from all the machine elements in the model – from dipolar + quadrupolar impedance In multibunch, the actual tune shift to be observed in the machine is lower in IR3MBC w.r.t phase 1. → Due to compensation between quadrupolar and dipolar impedances for the most critical horizontal collimators. The same kind of compensation occurs for single-bunch tune shift (-2e-4 in vertical, vs -3e-4 in phase 1) so no TMCI issue ?

  5. Headtail simulations for single-bunch TMCI threshold IR3MBC - vertical Phase 1 - horizontal The TMCI threshold seems to be 1.7e11 p/bunch in IR3MBC (in vertical) vs 3.4e11 p/bunch in phase 1 (in horizontal). In IR3MBC, it is due to a coupling between m=0 and m=-1 headtail mode, the m=-1 mode being shifted positively strange results, but if true, we don’t have any more margin for ultimate intensity …

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