Final focus system tuning studies towards Compact Linear Collider feasibility

In this paper we present the latest results regarding the tuning study of the baseline design of the final focus system of the Compact Linear Collider (CLIC-FFS). CLIC aims to provide collisions to the experiments at a luminosity above ${10}^{34}\mathrm{c}{\mathrm{m}}^{-2}{\mathrm{s}}^{-1}$. In order to deliver such luminosity in a single pass machine, the vertical beam size at the interaction point (IP) is reduced to about 1 nm, which imposes unprecedented tuning difficulties to the system. In previous studies, 90% of the machines reached 90% of the nominal luminosity at the expense of 18 000 luminosity measurements, when considering beam position monitor errors and transverse misalignments of magnets for a single beam case. In the present study, additional static imperfections such as roll misalignments and strength errors are included. Moreover both $e^{-}$ and $e^{+}$ beamlines are properly simulated. A new tuning procedure based on linear and nonlinear knobs is implemented to effectively cure the most relevant beam size aberrations at the IP. The obtained results for single and double beam studies under solely static imperfections are presented.

Figure 1

Cumulative histograms over 100 IP beam distributions of ${\sigma }_x^{*}$ (top) and ${\sigma }_y^{*}$ (bottom), when the second order correlations are individually removed.

Figure 2

Variation of $T_{126}$ (red), $T_{322}$ (green), $T_{122}$ (blue) and $T_{346}$ (cyan) correlations when scanning the $T_{126}$, $T_{322}$, $T_{122}$ and $T_{346}$ knobs from bottom to top plots.

Figure 3

Relative beam position offsets at the IP.

Figure 4

Tuning results for single beam case study. Red curve shows the accumulated luminosity histogram after BBA. Green, blue, and black curves represent the maximum luminosity obtained by scanning 1st, 2nd, and 3rd order knobs, respectively.

Figure 5

Tuning convergence for single (red) and double (blue) beam studies. Each dot is the mean value of 100 machines, while the error bar is the standard deviation at each scan.

Figure 6

Tuning results for the double beam study. Red curve shows the accumulated luminosity histogram after BBA. Green, blue and black curves represent the maximum luminosity obtained by scanning 1st, 2nd, and 3rd order knobs, respectively.

Figure 7

Obtained luminosity error assuming an error-free CLIC-FFS lattice as a function of number of particles in the bunch. Each dot is the standard deviation of 100 luminosity calculations obtained by GUINEA-PIG after tracking 100 different bunches.