Comparison of different tracking codes for beam delivery systems of linear colliders

The vertical RMS spot sizes at the interaction point of linear colliders are in the 1 nm to 5 nm range at beam en-ergies from 0.25 TeV to 1.5 TeV. Numerical tracking of particles through the magnetic focusing systems is used for the design and the performance prediction of the magnetic systems. In view of the small spot sizes and the high beam energies, it is important that the numerical codes include a careful treatment of the chromatic magnet properties and an accurate modelling of synchrotron radiation. Signifi-cant differences in the results of various codes have been observed and some fixes have been applied. In order to es-tablish a basis for future simulations, the results of various tracking and modelling codes are compared for identical input.