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arXiv · 2604.18466

pyTRAIN -- a modern TRAIN implementation

Michi Hostettler·Xavier Buffat·Tobias Persson·Tatiana Pieloni·Jorg Wenninger
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Abstract

The TRAIN code, developed in 1995 as a post-processor for second-order transport maps from MAD, has been used extensively at the LEP and the LHC to study self-consistent closed orbits, tunes and chromaticities of bunch trains under the presence of beam-beam long-range (BBLR) and PACMAN effects.. This paper presents a modern re-implementation of the TRAIN concept in Python using well-known numeric libraries (numpy, scipy) and an optional link to MAD-X via cpymad. This greatly improves the usability, maintainability and extensibility of the code. New functionality includes the support for arbitrary particle types, an arbitrary number and distribution of beam-beam interaction points, and the extrapolation of the beam-beam induced closed-orbit effects to arbitrary points in the machine. The code is benchmarked against the classic TRAIN code, and simulation results are compared to observations from LHC physics operation.

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Michi Hostettler, Xavier Buffat, Tobias Persson, Tatiana Pieloni, Jorg Wenninger. 2026-04-20. pyTRAIN -- a modern TRAIN implementation. https://arxiv.org/abs/2604.18466

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