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McStas: Guide_multichannel

[ Identification | Description | Input parameters | Links ]

The Guide_multichannel Component

Multichannel neutron guide with semi-transparent blades. Derived from Guide_channeled by Christian Nielsen. Allows to simulate bi-spectral extraction optics.


  • Site:
  • Author: Jan Saroun (
  • Origin: Nuclear Physics Institute, CAS, Rez
  • Date: 17.3.2022


Models a rectangular guide with equidistant vertical blades of finite thickness.
The blades material can be either fully absorbing or semi-transparent. The absorption
coefficient is wavelength dependent according to the semi-empirical model used
e.g. in J. Baker et al., J. Appl. Cryst. 41 (2008) 1003 or
A. Freund, Nucl. Instr. Meth. A 213 (1983) 495.
Data are provided for Si and Al2O3.

All walls are flat, curvature is not implemented (may be added as a future upgrade)
Tapering is possible by setting different entry ad exit dimensions.
Different guide coating can be set for vertical and horizontal mirrors.
For transparent walls, neutrons are alloed to migrate between channels and to
propagate through the blades.

The model is almost equivalent to the GUIDE component in SIMRES (
when used with zero curvature and type set to "guide or bender".
The features from SIMRES not included in this McSas model are:
- has a more conservative model for absorption in blades: events above r(m

Input parameters

Parameters in boldface are required; the others are optional.
w1(m) Width at the guide entry
h1(m) Height at the guide entry
w2(m) Width at the guide exit0
h2(m) Height at the guide exit0
l(m) Length of guide
R0(1) Low-angle reflectivity0.995
Qc(AA-1) Critical scattering vector0
alpha(AA) Slope of reflectivity0
m(1) m-value of material. Zero means completely absorbing.0
nslit(1) Number of channels in the guide (>= 1)1
dlam(m) Thickness of lamellae0.0005
Qcx(AA-1) Critical scattering vector for left and right vertical0.0218
Qcy(AA-1) Critical scattering vector for top and bottom mirrors0.0218
alphax(AA) Slope of reflectivity for left and right vertical4.38
alphay(AA) Slope of reflectivity for top and bottom mirrors4.38
W(AA-1) Width of supermirror cut-off for all mirrors0.003
mx(1) m-value of material for left and right vertical mirrors1
my(1) m-value of material for top and bottom mirrors. Zero1
mater(string) "Si", "Al2O3", or "absorb" (default)"absorb"


[ Identification | Description | Input parameters | Links ]

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

Last Modified: Wednesday, 03-Jan-2024 19:59:10 CET
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