Module Spin Reset

# VITESS Module Spin Reset

The module spin_reset (folder 'trajectories') is meant to reset the quantization direction of the spin at any point of the instrument. The quantization direction is set in the source module. If the beamline is bent, this direction is not the same any more relative to the beamline. Example: If one sets the quantization direction to the x-direction (beam direction) in the source and has a curved guide of 5°, these directions will deviate by 5° after the curved guide. But some modules require certain quantization directions relative to the surface. If the module spin_reset is used after the curved guide, the quantization direction can now be set along the beamline again, i.e. into the new x-direction.

A second option has been added to the module spin_reset: the colour marking certain trajectories can be reset. The property 'colour' of the neutron trajectories is used in many modules to mark trajectories in order to distinguish them later on, e.g. by monitoring or evaluating only trajectories of a certain colour.
Examples are:
source : mark the moderator that the trajectory comes from
chopper: mark the window that the trajectory passes
guide  : count the number of reflections
sample (environment): distinguish between different scattering events
As one might investigate more than one of these effects in an instrument, it is necessary to reset the colour. If you give '1' as 'number of colours', all trajectories will set to colour 1. If you give 'N' colours, trajectory i (i>=1) will get colour (i mod N), i.e. the first will get colour 1, the second colour 2, ... the Nthe number 'N', the (N+1)th again colour 1, and so on.

### Parameters for module 'spin_reset'

Parameter Unit | Description | Range or Values | Command Option
degree of polarization [%] | percentage of polarisation: 0% unpolarized, 100% all spins point into the same direction | [0,100] | -P
polarisation direction X Y Z | X-, Y and Z-component of the polarisation direction, the norm of the vector should be 1 | [0,1] | -X -Y -Z
number of colours | if zero, nothing happens if greater zero, the colour of the trajectories will be reset (to a value between 1 and this number) (for details see text above) | >=0 | -c

Back to VITESS overview
vitess@helmholtz-berlin.de

Last modified: Tue May 8 17:08:06 MET DST 2001