Final-focus systems for multi-TeV linear colliders

In Phys. Rev. Lett. 86, 3779 (2001), a compact final focus system (FFS) was presented. This scheme was compared to the nonlocal chromatic correction FFS concluding with the superiority of the local system. Nevertheless, the sensitivity of the system to errors and its mitigation was missing in the comparison. In this paper, an extended comparison of the Compact Linear Collider local FFS and an improved nonlocal FFS is presented at 3 TeV and 500 GeV. We demonstrate that, at high energies, luminosity delivered by the ideal machine is no longer the most important figure of merit but the recovered luminosity after tuning with imperfections, where the improved traditional scheme shows a better performance. This result might have an important relevance also for ILC at 1 TeV.