Effect of Collision Pattern in the LHC on the Beam Stability: Requirements from Experiments and Operational Considerations

Coherent instabilities of bunches in the LHC bunch train can be observed when the tune spread from beam-beam interactions becomes insufficient to ensure Landau damping. In particular these effects are seen on bunches with a reduced number of beam-beam interactions due to their collision pattern. Furthermore, such a reduction of the necessary stability can occur during the processes when the beams are prepared for collisions or during the optimization procedure. We discuss observations and possible countermeasures, in particular alternatives to the existing beam manipulation processes where such a situation can occur.