The Software Package VITESS for Neutron Instrument Simulations
The program VITESS simulates the trace of neutrons through a neutron scattering instrument. It is used for instrument design and optimization at many neutron sources including MLZ, ESS, and ILL and also for concept studies of novel neutron sources such as HBS. It also enables virtual neutron scattering instruments in preparation for an experiment or in the education of students. It is released under GNU public license.
Nearly all existing components and many types of samples are available in VITESS. Beginners can run it from GUI without compiling or writing any kind of script. Advanced users can use (python) scripts for parameter scans or (numerical) optimization.
Simulations for ESS
The instruments DREAM and T-REX of the new European neutron source ESS were simulated using VITESS. The figure shows the intensity as a function of wavelength (x-axis) and horizontal divergence (y-axis) after the switch of DREAM, which merges the beams from cold and thermal moderators. The switch consists of a neutron mirror, that couples the neutrons originating from the cold moderator into the neutron guide, while neutrons from the thermal pass straight through the mirror into the neutron guide. As a result the instrumental capabilities are increased thanks to the extended spectral range.
Simulations for HBS
Forschungszentrum Jülich is developing a new type of accelerator-based neutron source, called the High Brilliance Neutron Source (HBS). VITESS simulations of instruments are crucial to evaluate the performance of such a novel source. New results of the neutronic optimisation are regularly included in VITESS. The figure shows the angular intensity distribution at the sample position for a dedicated diffractometer for disordered and nano materials.
The current version is VITESS 3.4. Version 3.5 will be released soon. Additionally, VITESS 4 with a major upgrade (Qt GUI, instrument saved in yamlfiles, …) is under development.