Module Velselect

# VITESS Module Velselect

The module velselect simulates a mechanical velocity selector usually used for a CWS-SANS instrument.
The velocity selector front is parallel to the yz-plane with distance =0 from the origin provided by the
former module. After a neutron has crossed the velocity selector the orientation, y and z coordinates
of the origin are maintained, while x will be set to 0. The subsequent module refers therewith to a new
origin with unaltered y- and z-values at the exit of the velocity selector (i.e. the old origin is shifted
simply along the x-axis according to the length of the velocity selector).

This module will lead to correct results, if and only if all incoming neutrons already lie in a (y-z)window
on the upper half of the velocity selector front , therefore only the modules guide, window or source can define a
correct input for the velselect module.
Input neutrons which are not covered by the vel. selector front are not written to the output stream.

The following information has to be given as an input:

length of velselect [cm] | length of velocity selector [cm]
rotations/sec | number of rotations per second
number of channels | number of velocity selector channels
curvature | curvature of velocity selector channels
radius [cm] | radius of the velocity selector front
vert. distance axle to origin [cm] | same principle as for the chopper module (see in chopper help manual, Fig. 2 and accordant descriptions), just interpret the chopper disk as the velocity selector front.
spacer width [cm] | width of a spacer which separates the channels of the velocity selector.

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Last modified: Tue May 8 17:08:05 MET DST 2001