At the LHC, the interplay between a series of effects (e.g. intrabeam scattering, longitudinal beam manipulations, machine non-linearities) can lead to a tails population change, that may result in non-Gaussian beam distributions. Since the calculated beam size depends on the tail formation, it is important to follow the bunch profile evolution. In this paper, the benchmarking of a Monte-Carlo simulation code able to track 3D particle distributions, with the analytical IBS formulas is discussed. Novel distribution functions are employed to describe the beam profiles, and are used as a guideline for generalizing emittance estimations due to IBS and radiation effects. The impact of the distribution shape on the evolution of the bunch characteristics is studied. Bunch profile observations from the LHC Run 2 are compared to simulations and analytical results.
One of the main challenges of the lattice design of e + e − synchrotrons, used as light sources or damping rings, is the minimization of the emittance. The optimal configurations for achieving the absolute minimum emittance are the theoretical minimum emittance (TME) cells. This paper elaborates the optimization strategy in order to further reduce the betatron emittance of a TME cell by using dipoles whose magnetic field varies longitudinally. Based on the analytical results, the magnet design for the fabrication of variable bend with the optimal characteristics is discussed. In order to have a global understanding of all cell properties, the analytical approach for the theoretical minimum emittance (TME) cells with variable bends is presented. Numerical examples for the linear optimization of the Compact Linear Collider (CLIC) damping rings (DRs) are shown. The margin provided by this new design strategy on the output beam parameters after including the dominant effect of intrabeam scattering, enables the removal of a number of TME cells from the existing arcs while still keeping the requirements of the collider. The reduction of the circumference is further enhanced by the use of optimized high-field wigglers. The optimization strategy followed for the CLIC DRs is explained in detail and the output parameters of the new design are presented.
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