K-modulation in the LHC arcs?

The potential benefit for LHC from a K-modulation in the arc quadrupoles depends strongly on the quality of the machine alignment. If the magnet field and alignment stay within the specified tolerances, there is no need for a K-modulation as long as the r.m.s. BPM misalignment is smaller than 1mm. For larger values, the nominal beam cannot be accommodated. The resulting luminosity loss is off the order of 50% for an r.mn.s. BPM misalignment of 2 mm. If K-modulation in the arc is not implemented and if the nominal magnet tolerances cannot be met, efforts must be invested both in management of the survey alignment data and in exploitation of closed orbit measurements. Special alignment optics with a small phase advance could help the orbit analysis.