SixTrack Version 5: Status and New Developments

Abstract

SixTrack Version 5 is a major SixTrack release that introduces new features, with improved integration of the existing ones, and extensive code restructuring. New features include dynamic-memory management, scattering-routine integration, a new initial-condition module, and reviewed post-processing methods. Existing features like on-line aperture checking and Fluka-coupling are now enabled by default. Extensive performance regression tests have been developed and deployed as part of the new-release generation. The new features of the tracking environment developed for the massive numerical simulations will be discussed as well. 1. Main features SixTrack [1] is a 6D single-particle symplectic tracking code for studying dynamic aperture (DA) or evaluating the performance of beam-intercepting devices like collimators [2]. SixTrack is licensed as GNU Lesser General Public License software and is under very active development in the GitHub repository [3]. Extensive restructuring and new features have been added in the last years. The SixDesk runtime environment manages SixTrack simulations from input generation, job queue management (using HTCondor [4] in the CERN BATCH service [5] and customised software in the CERN BOINC server [6]), to collecting and post-processing results. This paper presents a summary of the existing features in the last SixTrack and SixDesk releases and focuses on some of the most recent developments. SixTrack computes very efficiently the trajectories of individual relativistic charged particles in circular accelerators by using explicitly 6D symplectic maps (see [7] and references therein), or scattering elements. The set of coordinates used internally is larger than the minimum needed to describe the motion. Additional variables are used to store energy-related quantities and are updated only on energy changes, which do not occur very frequently in synchrotrons in the absence of radiation effects, to save computational time. Thick maps for dipoles and quadrupoles also reuse the energy-dependent factors of the firstand second-order polynomials of the map that are recalculated at each energy change. Furthermore, different ion species can be tracked at the same time using an extension of the usual symplectic formalism (see later). 10th International Particle Accelerator Conference Journal of Physics: Conference Series 1350 (2019) 012129 IOP Publishing doi:10.1088/1742-6596/1350/1/012129 2 SixTrack tracking maps are optimised for speed and numerical reproducibility. Scattering maps are being re-factored to be numerically reproducible, thus increasing the type of simulations that can be ported to LHC@Home [8]. SixTrack can also be linked with the BOINC library [6] to use the volunteer computing project LHC@Home. SixTrack can compute linear and non-linear optical functions using a 5D matrix code and a 6D truncated power series algebra (TPSA) tracking code. Coupled Twiss parameters, using the Mais-Ripken formalism [9], can be extracted along the lattice. The optical parameters are optionally used in the beam-beam elements for self-consistent simulations. Differently from other codes, SixTrack uses (σ = s − β0 c t) as the longitudinal coordinate during tracking to avoid rounding errors associated to the relativistic β when updating time delays in drifts and ( ζ = β β0σ, δ = P−P0 P0 ) as conjugate canonical variables in 6D optics