The Simulation Package VITESS

Concept

VITESS has thus a modular structure consisting of independently executable program components (e.g. source, guide, chopper, polarizer, sample, focussing monochromator/analyser, etc). Each module processes the neutron beam input and the output neutron beam is a function of the parameters chosen for that respective module. For example, the number of neutrons that are lost in a guide segment depends on its geometry parameters and the coating of its surfaces.

The neutron beam input and output represent an optionally large number of neutron trajectories each of which is described by 12 coordinates:

time, lambda, probability weight, position (x, y, z), direction (cos(alpha), cos(beta), cos(gamma)) and Spin (S_x, S_y, S_z)

These 12 parameters per neutron trajectory are consecutively written to or read from the stream in a double precision binary form. By sticking to some conventions you can not only use the provided executables, but also write and add your own ones in order to study the characteristics of the neutrons anywhere in your instrument according to your needs. To understand how your modules fit to the framework you may read the report on VITESS Software Technique (PDF).

 

 

 

 

 

Fig.2: Ratio of flux at the end of the straight guide for kinks with different coatings and offset angles of the outer (= reflecting) mirror and for a curved guide relative to flux without kink