[ 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.

Identification

• Site:
• Author: Jan Saroun (saroun@ujf.cas.cz)
• Origin: Nuclear Physics Institute, CAS, Rez
• Date: 17.3.2022

Description

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 (http://neutron.ujf.cas.cz/restrax)
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.


 
Name
Unit
Description
Default


 
w1
m
Width at the guide entry

 
h1
m
Height at the guide entry

 
w2
m
Width at the guide exit
0

 
h2
m
Height at the guide exit
0

 
l
m
Length of guide

 
R0
1
Low-angle reflectivity
0.995

 
Qc
AA-1
Critical scattering vector
0

 
alpha
AA
Slope of reflectivity
0

 
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 lamellae
0.0005

 
Qcx
AA-1
Critical scattering vector for left and right vertical mirrors in each channel
0.0218

 
Qcy
AA-1
Critical scattering vector for top and bottom mirrors
0.0218

 
alphax
AA
Slope of reflectivity for left and right vertical mirrors in each channel
4.38

 
alphay
AA
Slope of reflectivity for top and bottom mirrors
4.38

 
W
AA-1
Width of supermirror cut-off for all mirrors
0.003

 
mx
1
m-value of material for left and right vertical mirrors in each channel. Zero means completely absorbing.
1

 
my
1
m-value of material for top and bottom mirrors. Zero means completely absorbing.
1

 
mater
string
"Si", "Al2O3", or "absorb" (default)
"absorb"




  

  
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Links


  
 Source code for Guide_multichannel.comp.
  



 [ Identification
 | Description
 | Input parameters
 | Links ]



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 Last Modified: Friday, 12-Dec-2025 12:58:06 CET