Summary of MD on nominal collimator settings

The presently installed Phase 1 LHC collimators (1), were moved in the betatron cleaning insertion (IR7) from relaxed to nominal settings at 3.5TeV and further in. The collimator performance and impedance were measured. The local cleaning inefficiency improved from ~3e-4 (average relaxed settings) to 1e-4 (nominal settings), and 4e-5 (tight settings). In parallel, measurements of transverse betatron tune shifts during collimator movements were carried out to verify the transverse impedance model. Despite very large noise, preliminary analysis shows that the measured effective impedance may be slightly larger than expected. Dedicated measurements without transverse dampers are needed to improve the tune signal to noise ratio and conclude on the effective impedance of the collimators at 3.5 TeV. The significant performance improvement with tight settings could be used to allow for a higher intensity in the machine. Tighter collimator settings could allow operations with smaller β* in the experimental insertion regions.