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McStas: Monochromator_curved Component

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

The Monochromator_curved Component

Double bent multiple crystal slabs with anisotropic gaussian mosaic.


  • Author: Emmanuel Farhi, Kim, Lefmann, Peter Link
  • Origin: ILL
  • Date: Aug. 24th 2001
  • Version: $Revision$
  • Modification history:
    • EF, Aug. 24th 2001: From Mosaic_anisotropic and Mon_2foc
    • EF, Feb 13th 2002: Read reflectivity table
    • EF, Oct 24th 2002: Read transmission table


Double bent infinitely thin mosaic crystal, useful as a monochromator or
analyzer. which uses a small-mosaicity approximation and taking into account
higher  order scattering. The mosaic is anisotropic gaussian, with different
FWHMs in the Y and Z directions. The scattering vector is perpendicular to the
surface. For an unrotated monochromator component, the crystal plane lies in
the y-z plane (ie. parallel to the beam). The component works in reflection, but
also transmits the non-diffracted beam. Reflectivity and transmission files may
be used. The slabs are positioned in the vertical plane (not on a
cylinder/sphere), and are rotated according to the curvature radius.
When curvatures are set to 0, the monochromator is flat.
The curvatures approximation for parallel beam focusing to distance L, with
monochromator rotation angle A1 are:
  RV = 2*L*sin(DEG2RAD*A1);
  RH = 2*L/sin(DEG2RAD*A1);

When you rotate the component by A1 = asin(Q/2/Ki)*RAD2DEG, do not forget to
rotate the following components by A2=2*A1 (for 1st order) !

Example: Monochromator_curved(zwidth=0.01, yheight=0.01, gap=0.0005,
          NH=11, NV=11, mosaich=30.0, mosaicv=30.0, r0=0.7, Q=1.8734)

Monochromator lattice parameter
PG       002 DM=3.355 AA (Highly Oriented Pyrolythic Graphite)
PG       004 DM=1.677 AA
Heusler  111 DM=3.362 AA (Cu2MnAl)
CoFe         DM=1.771 AA (Co0.92Fe0.08)
Ge       111 DM=3.266 AA
Ge       311 DM=1.714 AA
Ge       511 DM=1.089 AA
Ge       533 DM=0.863 AA
Si       111 DM=3.135 AA
Cu       111 DM=2.087 AA
Cu       002 DM=1.807 AA
Cu       220 DM=1.278 AA
Cu       111 DM=2.095 AA

Input parameters

Parameters in boldface are required; the others are optional.
Name Unit Description Default
reflect str reflectivity file name of text file as 2 columns [k, R] "NULL"
transmit str transmission file name of text file as 2 columns [k, T] "NULL"
zwidth m horizontal width of an individual slab 0.01
yheight m vertical height of an individual slab 0.01
gap m typical gap between adjacent slabs 0.0005
NH columns number of slabs horizontal 11
NV rows number of slabs vertical 11
mosaich arc minutes Horisontal mosaic FWHM 30.0
mosaicv arc minutes Vertical mosaic FWHM 30.0
r0 1 Maximum reflectivity. O unactivates component 0.7
t0 1 transmission efficiency 1.0
Q AA-1 Scattering vector 1.8734
RV m radius of vertical focussing. flat for 0 0
RH m radius of horizontal focussing. flat for 0 0
DM Angstrom monochromator d-spacing instead of Q=2*pi/DM 0
mosaic arc minutes sets mosaich=mosaicv 0
width m total width of monochromator, along Z 0
height m total height of monochromator, along Y 0
verbose 0/1 verbosity level 0
order 1 specify the diffraction order, 1 is usually prefered. Use 0 for all 0

Output parameters

Name Unit Description Default
row 1:NV row index for last hit blade  
col 1:NH column index for last hit blade  


  • Source code for Monochromator_curved.comp.
  • Additional note from Peter Link.
  • Obsolete Mosaic_anisotropic by Kristian Nielsen
  • Contributed Monochromator_2foc by Peter Link

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

Generated automatically by McDoc, Peter Willendrup <> / Fri Mar 17 20:40:06 2017

Last Modified: Friday, 17-Mar-2017 21:40:06 CET
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