Abstract
The VITESS software package is a useful tool for the development of neutron scattering instruments. Although initially intended to assist in designing new instruments for the European Spallation Source, it can also be used effectively to simulate complex instrument set-ups at continuous, short-pulsed or long-pulsed sources. This article outlines the conceptual design of the VITESS program and describes new features included in the most recent version of the package, VITESS 2.10. These include the possibility to split parts of the simulation into several threads which improves efficiency on multi-processor computers. New components for elliptic mirrors, lenses and beam-stops have been added. The neutron guide module now permits the visualization of neutron trajectories. Results of the simulation of the EXED instrument at Helmholtz-Zentrum Berlin are presented as an example of the program's use. New features implemented in release 2.11 or planned for release 3 are described.