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McStas: Monochromator_curved

[ Identification | Description | Input parameters | Links ]

The Monochromator_curved Component

Double bent multiple crystal slabs with anisotropic gaussian mosaic.


  • Site:
  • Author: Emmanuel Farhi, Kim, Lefmann, Peter Link
  • Origin: ILL
  • Date: Aug. 24th 2001


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.
reflectstrreflectivity file name of text file as 2 columns [k, R]"NULL"
transmitstrtransmission file name of text file as 2 columns [k, T]"NULL"
zwidthmhorizontal width of an individual slab0.01
yheightmvertical height of an individual slab0.01
gapmtypical gap between adjacent slabs0.0005
NHintnumber of slabs horizontal11
NVintnumber of slabs vertical11
mosaicharc minutesHorisontal mosaic FWHM30.0
mosaicvarc minutesVertical mosaic FWHM30.0
r01Maximum reflectivity. O unactivates component0.7
t01transmission efficiency1.0
QAA-1Scattering vector1.8734
RVmradius of vertical focussing. flat for 00
RHmradius of horizontal focussing. flat for 00
DMAAmonochromator d-spacing instead of Q=2*pi/DM0
mosaicarc minutessets mosaich=mosaicv0
widthmtotal width of monochromator, along Z0
heightmtotal height of monochromator, along Y0
verbose0/1verbosity level0
order1specify the diffraction order, 1 is usually prefered. Use 0 for all0


  • 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 | Links ]

Generated on 2024-01-03 11:47:43

Last Modified: Wednesday, 03-Jan-2024 19:59:11 CET
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