Polarising bender.
Author: Erik Bergbaeck Knudsen (erkn@fysik.dtu.dk)
Origin: DTU Physics
Date: June 2012
A component modelling a set of identical blades bent to form a multcihannel (nslits) bender. The bender has a cylindrically curved entry plane (Will be extended to also allow a flat entry plane).
The bender may also be tapered such that it can have focusing or defocusing porperties. This may be specified through the "channel_file"-parameter, which points to a data file in which the individual channels are defined by an entry- and an exit-width.
The file format for channel file columns: > #d-spacing1 d-spacing2 l_spacer d-coating1 d-coating2
> 1e-3 0.8e-3 1e-5 1e-9 1e-9
Each blades is considered coated with a reflecting coating, whose thickness is defined in the latter two columsn of the channel data file.
Coating reflectivities are read from another data file with separate reflectivities for up and down spin. When a neutron ray hits a blade the polarization vector associated with the ray is decomposed into spin-up and down probablities, which in turn determines the overall reflectivity for this ray on the mirror. Furthermore the probabilities are used to also reconstruct the polarization vector of the reflected ray.
File format for the reflectivity file: > #parameter = m > q/m R(up) R(down)
The effect of spacers inside the channels is modelled by absorption only. The depth of the spacers in a channel is considered constant for one channel (set in the channel data file), the number of them is constant across all channels and is an input parameter to the component.
Parameters in boldface are required; the others are optional.
|
Name |
Unit |
Description |
Default |
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channel_file |
|
File name of file containing channel data. such as spacer widths etc. (see above for format) |
"channel.dat" |
|
xwidth |
m |
Width at the bender entry. Currently unsupported. |
0 |
|
yheight |
m |
Height at the bender entry. |
|
|
length |
m |
Length of blades that make up the bender. |
|
|
d_substrate |
m |
Thickness of the substrate. |
|
|
entry_radius |
m |
Radius of curvature of the entrance window. |
10 |
|
radius |
m |
Curvature of a single plate/polarizer. +:curve left/-:right |
100 |
|
G |
m/s\(^{2}\) |
Magnitude of gravitation. |
9.8 |
|
nslit |
1 |
Number of slits in the bender |
1 |
|
debug |
|
If > 0 print out some internal parameters. |
1 |
|
reflect_file |
|
File name of file containing reflectivity data parametrized either by q or m. |
NULL |
|
sigma_abs |
barn |
Absorption per unit cell at v=2200 m/s of spacers. Defaults to literature value for Al. |
0.231 |
|
V0 |
Å\(^{3}\) |
Volume of unit cell for spacers. Defaults to Al. |
66.4 |
|
nspacer |
|
Number of spacers per channel. |
5 |
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Component source code found in file Pol_bender_tapering.comp.