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

We present a new conceptual and optical design for the Next Linear Colliderpost-linac collimation system. Energy collimation and passive protectionagainst off-energy beams are achieved in a system with large horizontaldispersion and vertical betatron functions. Betatron collimation is performedin a relatively low-beta (FODO-like) lattice in which only thin spoilersintercept particles near the beam core, while thick absorbers maintain a largestay-clear from the beam. Two possible schemes for the spoilers are considered:one in which the spoilers are capable of tolerating a certain number ofdamaging interceptions per collider run ("consumable" spoilers), and one inwhich the spoilers are potentially damaged on every machine pulse and areself-repairing ("renewable" spoilers). The collimation efficiency of the systemis evaluated, considering both halo particles which are rescattered into thebeam and muon secondaries which are passed to the interaction region. Weconclude that the new design is a promising candidate for the NLC post-linacsystem.