Damping of phase errors at injection in the LHC

Capture losses must be kept to an extremely small value in the superconducting, very high intensity (0.85A per beam) LHC machine. Bunches from the injector (the SPS accelerator) are fairly long (51 cm full length compared to the RF wavelength of 75 cm) and phase injection errors may bring the edge of the injected bunch very close to the separatrix. Following the SPS collider experience, it is therefore of prime importance to quickly damp any phase (or energy) error at injection in order to avoid capture losses as much as possible. The main LHC RF system is composed of eight single cell 400 MHz superconducting cavities, which are common to both beams and cannot be used to act independently on a newly injected batch. Dedicated cavities (or longitudinal kickers) working on each beam separately will provide damping of phase oscillations just after injection; they may also be used to suppress any coupled bunch longitudinal instability during coast