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)
N. Mounet, B. Salvant and E. Métral - ICE meeting - 15/09/2010

2. Better in horizontal, but…
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…
N. Mounet, B. Salvant and E. Métral - ICE meeting - 15/09/2010

3. BUT this is supposed to be damped by transverse feedback.
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) ?
N. Mounet, B. Salvant and E. Métral - ICE meeting - 15/09/2010

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 ?
N. Mounet, B. Salvant and E. Métral - ICE meeting - 15/09/2010

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 …
N. Mounet, B. Salvant and E. Métral - ICE meeting - 15/09/2010