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

This preliminary study presents a comparative analysis of Phase 1 and IR3MBC in the LHC, focusing on combined momentum and betatron cleaning settings as provided by A. Rossi. Key findings indicate effects on coupled-bunch modes from various machine elements, including collimators, magnets, and beam screens. Notably, a lower tune shift is observed in the IR3MBC configuration compared to Phase 1, attributed to compensation between quadrupolar and dipolar impedances. The TMCI threshold shows significant variation, emphasizing the need for further investigation into transverse feedback mechanisms.

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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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