VITESS Module Polarizing Mirror


The module pol_mirror simulates one plane mirror that might have different reflectivity curves for spin-up and spin-down neutrons. The transmitted or the reflected beam can be regarded. The co-ordinate system of the following module has to be set accordingly. Size, position and orientation of the mirror as well as the reflectivity curves for spin-up and spin-down neutrons have to be given. In addition, the spin quantization direction has to be defined.
The orientation of the mirror can only be set in 2 different ways: a) rotation about the y-axis starting from a horizontal orientation (in x-y-plane) b) rotation about the z-axis starting from a vertical orientation (in x-z-plane) Absorption is not considered. If absorption inside a mirror has to be taken into account or an orientation is needed that is not accessible in the way described, the more advanced module sm_ensemble has to be used.

The reflected fraction of the neutrons is calculated according to the formula
    prefl = (aup*cos(&theta/2)2 + (adown*sin(&theta/2)2

&theta is the the polar angle relative to the quantization direction. aup = sqrt(Rup) is the square root of the reflectivity of spin-up neutrons and adown = sqrt(Rdown) the square root of the the reflectivity of the spin-down neutrons.

The orientation of the transmitted or reflected beam is given by

    &thetaout,trans = 2 atan ( (1-adown) / (1-aup) * tan(&theta/2) )

    &thetaout,refl  = 2 atan ( adown / aup * tan(&theta/2) )

Parameters for module 'pol_mirror'


Parameter
Unit
Description
Range or Values
Command Option
up-/down-reflectivity file input data file containing the reflectivity curve R(Q) for spin-up and for spin-down neutrons resp. (in the same form as it is used for guide module) - -U
-D
mode criterion: use of transmitted or reflected beam. transmission
reflection
-T
length
[cm]
length of the polarizing mirror (i.e. along beam axis) >0 -L
position X, Y, Z,
[cm]
x-, y- and z-position of the center of the polarizing mirror (in the input frame) any -X
-Y
-Z
inclination
[deg]
rotation angle of the polarizing mirror relative to the beam axis (see text) [-180°,180] -V
orientation choice between vertical and horizontal orientation of the mirror (see text) 'horizontal', 'vertical' -O
analysis dir. X, Y, Z x-, y- and z-component of the quantization direction any -a
-b
-c
output X, Y, Z,
[cm]
x-, y- and z-position of the output frame (in the input frame) any -x
-y
-z
horiz.
vert. rotation angle
[deg]
rotation angle of the output frame relative to the input frame in horizontal and vertical direction [-180°,180] -h
-v



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