Module Polarizer Supermirror

# VITESS Module Polarizer Supermirror

This module simulates a multichannel supermirror polarizer with flat channel walls tilted by an angle relative to the neutron beam in order to reflect all neutrons at least one time.
The polarization process at each reflection is treated quantummechanically:

qnew = 2. * atan(aDD/ aUU * tan(q/2.)) ;

where

aUU = sqrt(rupdata[datanumber]) ;

aDD = sqrt(rdowndata[datanumber]) ;

are the diagonal components of the polarization scattering matrix and rupdata[datanumber] and rdowndata[datanumber] give the "Up" and "Down" reflectivities belonging to the wavelength bin (numero 'datanumber') as read from the reflectivity files.
The probability weight is multiplied by the probability of reflection in function of the wavelength:

Prob =Prob * (sq(aUU * cos(q/2.)) + sq(aDD * sin(q/2.)) );

and this simplifies to Prob = Prob * RUp,Down in case of only "Up" or "Down" trajectories, when q is 0 or p.

The spin precessions are approximated classically i.e. we rotate the spin vectors belonging to the trajectories in order to simulate dephasing in function of flight time through the magnetic field.

### Module parameters

Parameter Unit | Description | Command option Parameter file
parameter file | name of the parameter file | -P
Up-reflectivity file | reflectivity data file for Up neutrons; format as guide reflectivity file | -U
Down-reflectivity file | reflectivity data file for Down neutrons; format as guide reflectivity file | -D
position X, Y, Z [cm] | center position of the rectangular geometry polarizer | -a, -b, -c
horizontal, vertical offset [deg] | rotation angle of the polarizer in horizontal (first rotation) and vertical direction (0, 0 means parallel to X i.e. beam) | -H, -V
output X, Y, Z [cm] | position of the output frame (in the input frame) | -R, -E, -G
horizontal, vertical rotation angle [deg] | rotation angle of the output frame in horizontal (first rotation) and vertical direction (0, 0 means parallel to original X) | -h, -v
dimension X, Y, Z [cm] | length, width and height of the polarizer | parameter file
number of channels | number of channels in vertical direction | parameter file
wall width [cm] | width of the wall between the channels | parameter file
guide field X, Y, Z [Oe] | components of the guide field | parameter file
analysis dir. X, Y, Z | direction vector components of the quantization direction | parameter file

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Last modified: Tue Jul 23 17:27:04 MEST 2002, G.Zs.