Studies of Beam Optics and Scattering in the Next Linear Collider Post-Linac Collimation System

The authors present a new conceptual and optical design for the Next Linear Collider post-linac collimation system. Energy collimation and passive protection against off-energy beams are achieved in a system with large horizontal dispersion and vertical betatron functions. Betatron collimation is performed in a relatively low-beta (FODO-like) lattice in which only thin spoilers intercept particles near the beam core, while thick absorbers maintain a large stay-clear from the beam. Two possible schemes for the spoilers are considered: one in which the spoilers are capable of tolerating a certain number of damaging interceptions per collider run (consumable spoilers), and one in which the spoilers are potentially damaged on every machine pulse and are self-repairing (renewable spoilers). The collimation efficiency of the system is evaluated, considering both halo particles which are rescattered into the beam and muon secondaries which are passed to the interaction region. The authors conclude that the new design is a promising candidate for the NLC post-linac system