Results on nominal collimator settings MD at 4 TeV

The goal of the MD performed on June 24th 2012 was to achieve the nominal 7 TeV settings in mm with nominal single bunch intensities using centers from the beam-based alignment of March 2012. The secondary collimators and absorbers in IR7 and the dump protection collimators were moved in from the current operational, ”tight” settings to the equivalent 7 TeV nominal settings in mm at 4 TeV, which are tighter than the current settings except for the TCPs. The performance of the nominal settings was investigated through loss maps using the ADT method to blow-up the beam. The loss maps showed a good cleaning in the dispersion suppressor regions for both beams. However, the cleaning hierarchy in beam 1 was not preserved. We tried to restore the hierarchy by re-aligning a sub-set of collimators in IR7 but no significant improvement was found. In addition, measurements on the transverse betatron tune shift during collimator movements were done in order to compare with the transverse impedance model in 2 cases: a) the secondary collimators at IR7 are moved in and out the beam line; b) the primary collimators in IR7 are moved in and out the beam line. Instability measurements were also performed.