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.

Figure 1

Optics of the CLIC 3 TeV local correction scheme (top) and dedicated correction scheme (bottom) final focus system showing the optical functions, where $\eta$ is the dispersion function. Above the layout is shown where in blue are represented bending magnets, in red quadrupoles and in black sextupoles.

Figure 2

Optics of the CLIC 500 GeV local correction scheme (top) and dedicated correction scheme (bottom) final focus system showing the optical functions. Above the layout is shown where in blue are represented bending magnets, in red quadrupoles and in black sextupoles.

Figure 3

High order optimization using MAPCLASS for CLIC FFS at 3 TeV (top) and 500 GeV (bottom).

Figure 4

Beam at the entrance of the final doublet for the local and the traditional FFS for CLIC at 3 TeV c.m. energy. Particles of the incoming beam are placed on an ellipsoid of $15{\sigma }_x$ and $50{\sigma }_y$ and a flat energy distribution with $1.4\%E_0$ width.

Figure 5

Peak luminosity bandwidth for different schemes of CLIC FFS at 3 TeV (top) and 500 GeV (bottom).

Figure 6

Luminosity distribution of 100 machines after BBA and Multiknob algorithm procedure for an initial prealignment of $10\mu \mathrm{m}$ for CLIC 3 TeV (top) and 500 GeV (bottom). Luminosity is normalized to the value given in Table 1.