Possible problems in Phase A.4:

1. Feedbacks for orbit, tune (and chromaticity) not working as expected.
   • Cause: Inaccurate optics model; problem with the BPM acquisition; problems with the software
   • Diagnostics: More detailed measurements of orbit, tune, ...
   • Remedies: Assess the orbit/optics stability: proceed without feedbacks, if possible. Perform more detailed commissioning of the required BI. Refine the optics model if needed.
2. Aperture too small - we cannot meet the target values.
   • Cause: optics is not under control (orbit or beta-beat out of tolerance); obstacles in the beam pipe; alignment errors
   • Diagnostics: More detailed aperture scans (identify losses+local scans)
   • Remedies: Identify the bottleneck(s); local scans + centring the closed-orbit at the aperture restriction; re-measure precisely the machine aperture and continue with the optimization. Understand if problems comes from optics or obstacles and act accordingly (optimize the orbit if necessary) . Can we further close the collimators to protect the reduced aperture? In case of serious obstacles/alignment errors: need to access the machine and possibly to open the vacuum.
     
3. Momentum aperture too small
   • Cause: Same as before.
   • Diagnostics: Same as before, see section on momentum aperture measurements.
   • Remedies: Same as before + commission the momentum collimators earlier.
4. Optics errors: large differences from the model; small dynamics aperture.
   • Cause: Errors from various sources. Alignment errors -> feed-down of higher order multipoles. Polarity issues. Transfer function errors.
   • Diagnostics: more detailed optics measurements to identify the source of errors.
   • Remedies: Refine optics model and correct errors. Re-align critical elements if needed? Use special alignment optics, e.g. for D1/D2 transfer functions.