Increasing the Integrated Luminosity of SLHC by Luminosity Levelling via the Crossing Angle

With an increase of luminosity by a factor of 10, the luminosity lifetime in an upgraded LHC would decrease from 15 hours to two to four hours, depending on the upgrade strategy. If the luminosity increase is achieved primarily by a stronger and more efficient focusing rather than a beam current increase, the luminosity lifetime is in the low bound of this range. We show in this paper that the "early separation" scheme and/or a crab crossing lend itself to a very efficient luminosity levelling. It can be used to counteract the faster luminosity decay and provide a constant luminosity over hours as well as a significant increase of integrated luminosity. This is achieved by adjusting the crossing angle rather than the b* function by means of a bump closed inside the experimental straight section, i.e. operationally simple. The initially large crossing angle reduces the beam-beam tune shift, allowing an increased beam current and higher performance with lower pile-up in the detector and lower energy deposition in the triplet. The impact of the large Piwinski angle required is first investigated.