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McStas: Pol_bender_tapering Component

[ Identification | Description | Input parameters | Output parameters | Links ]

The Pol_bender_tapering Component

Polarising bender.


  • Author: Erik Bergbaeck Knudsen (
  • Origin: DTU Physics
  • Date: June 2012
  • Version:(Unknown)


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

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.

WARNING: This is a contributed Component.

Input parameters

Parameters in boldface are required; the others are optional.
Name Unit Description Default
channel_file see above for format [ ] File name of file containing channel data. such as spacer widths etc. "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 9.8
nslit 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 AA^3 Volume of unit cell for spacers. Defaults to Al. 66.4
nspacer Number of spacers per channel. 5

Output parameters

Name Unit Description Default


[ Identification | Description | Input parameters | Output parameters | Links ]

Generated automatically by McDoc, Peter Willendrup <> / Fri Jan 18 10:06:10 2019

Last Modified: Friday, 18-Jan-2019 11:06:10 CET
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