McStas logo McStas - A neutron ray-trace simulation package ILL; PSI; ESS Niels Bohr Institute DTU Physics NEXMAP


About McStas
 Conditions of use
 Project funding

 Other Downloads (share)

Mailing list

Search web/mailinglist

 Wiki (GitHub)
 McStas manual


Report bugs (GitHub)

Code-repository (GitHub)

McStas: Pol_bender_tapering

[ Identification | Description | Input parameters | Links ]

The Pol_bender_tapering Component

Polarising bender.


  • Site:
  • Author: Erik Bergbaeck Knudsen (
  • 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

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.

Input parameters

Parameters in boldface are required; the others are optional.
channel_file File name of file containing channel data. such as spacer widths etc. (see above for format)"channel.dat"
xwidthmWidth at the bender entry. Currently unsupported.0
yheightmHeight at the bender entry.
lengthmLength of blades that make up the bender.
d_substratemThickness of the substrate.
entry_radiusmRadius of curvature of the entrance window.10
radiusmCurvature of a single plate/polarizer. +:curve left/-:right100
Gm/s^2Magnitude of gravitation.9.8
nslit1Number of slits in the bender1
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_absbarnAbsorption per unit cell at v=2200 m/s of spacers. Defaults to literature value for Al.0.231
V0AA^3Volume of unit cell for spacers. Defaults to Al.66.4
nspacer Number of spacers per channel.5


[ Identification | Description | Input parameters | Links ]

Generated on 2023-09-19 20:01:36

Last Modified: Wednesday, 03-Jan-2024 19:59:10 CET
Search website mailinglist archive GitHub repos