Collimators are not present in the deck yet. Virtually every technical issue listed above contains significant unknowns in the context of the collimation system. We have assumed a halo population of approx. 1e9 per bunch train based on SLC experience. System tolerances will be tight, though not as tight as in ZDR system or final focus.
Gaps are relatively conservative based upon fatigue considerations.
The present design is a compromise. This drove us to separate the energy and betatron systems as described. The large betay in the energy region drove us to add sextupoles and octupoles to that part of the system. Also, the energy collimation achieves its protection through linear optics rather than a nonlinear magnet of some form. Attempts to use such a nonlinear magnet were not successful, though not in principle precluded.