Neutron straight guide with gravity. Can be channeled and focusing. Waviness may be specified, as well as side chamfers (on substrate).
Author: <a href="mailto:farhi@ill.fr">Emmanuel Farhi</a>
Origin: <a href="http://www.ill.fr">ILL (France)</a>.
Date: Aug 03 2001
Models a rectangular straight guide tube centered on the Z axis, with gravitation handling. The entrance lies in the X-Y plane. The guide can be channeled (nslit,d,nhslit parameters). The guide coating specifications may be entered via different ways (global, or for each wall m-value).
Waviness (random) may be specified either globally or for each mirror type. Side chamfers (due to substrate processing) may be specified the same way. In order to model a realistic straight guide assembly, a long guide of length ’l’ may be splitted into ’nelements’ between which chamfers/gaps are positioned.
The reflectivity may be specified either using an analytical mode (see Component manual) or as a text file in free format, with 1st column as q[Å-1] and 2nd column as the reflectivity R in [0-1]. For details on the geometry calculation see the description in the McStas component manual.
There is a special rotating mode in order to approximate a Fermi Chopper behaviour, in the case the neutron trajectory is nearly linear inside the chopper slits, i.e. the neutrons are fast w/r/ to the chopper speed. Slits are straight, but may be super-mirror coated. In this case, the component is NOT centered, but located at its entry window. It should then be shifted by -l/2.
Example: Guide_gravity(w1=0.1, h1=0.1, w2=0.1, h2=0.1, l=12,
R0=0.99, Qc=0.0219, alpha=6.07, m=1.0, W=0.003)
%VALIDATION May 2005: extensive internal test, all problems solved Validated by: nslit. Lieutenant
Parameters in boldface are required; the others are optional.
|
Name |
Unit |
Description |
Default |
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|
w1 |
m |
Width at the guide entry |
|
|
h1 |
m |
Height at the guide entry |
|
|
w2 |
m |
Width at the guide exit. If 0, use w1. |
0 |
|
h2 |
m |
Height at the guide exit. If 0, use h1. |
0 |
|
l |
m |
length of guide |
|
|
R0 |
1 |
Low-angle reflectivity |
0.995 |
|
Qc |
Å\(^{-1}\) |
Critical scattering vector |
0.0218 |
|
alpha |
Å |
Slope of reflectivity |
4.38 |
|
m |
1 |
m-value of material. Zero means completely absorbing. m=0.65 glass/SiO2 Si Ni Ni58 supermirror Be Diamond m= 0.65 0.47 1 1.18 2-6 1.01 1.12 for glass/SiO2, m=1 for Ni, 1.2 for Ni58, m=2-6 for supermirror. m=0.47 for Si |
1.0 |
|
W |
Å\(^{-1}\) |
Width of supermirror cut-off |
0.003 |
|
nslit |
1 |
Number of vertical channels in the guide (>= 1) (nslit-1 vertical dividing walls). |
1 |
|
d |
m |
Thickness of subdividing walls |
0.0005 |
|
mleft |
1 |
m-value of material for left. vert. mirror |
-1 |
|
mright |
1 |
m-value of material for right. vert. mirror |
-1 |
|
mtop |
1 |
m-value of material for top. horz. mirror |
-1 |
|
mbottom |
1 |
m-value of material for bottom. horz. mirror |
-1 |
|
nhslit |
1 |
Number of horizontal channels in the guide (>= 1). (nhslit-1 horizontal dividing walls). this enables to have nslit*nhslit rectangular channels |
1 |
|
G |
m/s\(^{2}\) |
Gravitation norm. 0 value disables G effects. |
0 |
|
aleft |
1 |
alpha-value of left vert. mirror |
-1 |
|
aright |
1 |
alpha-value of right vert. mirror |
-1 |
|
atop |
1 |
alpha-value of top horz. mirror |
-1 |
|
abottom |
1 |
alpha-value of left horz. mirror |
-1 |
|
wavy |
deg |
Global guide waviness |
0 |
|
wavy_z |
deg |
Partial waviness along propagation axis |
0 |
|
wavy_tb |
deg |
Partial waviness in transverse direction for top/bottom mirrors |
0 |
|
wavy_lr |
deg |
Partial waviness in transverse direction for left/right mirrors |
0 |
|
chamfers |
m |
Global chamfers specifications (in/out/mirror sides). |
0 |
|
chamfers_z |
m |
Input and output chamfers |
0 |
|
chamfers_lr |
m |
Chamfers on left/right mirror sides |
0 |
|
chamfers_tb |
m |
Chamfers on top/bottom mirror sides |
0 |
|
nelements |
1 |
Number of sections in the guide (length l/nelements). |
1 |
|
nu |
Hz |
Rotation frequency (round/s) for Fermi Chopper approximation |
0 |
|
phase |
deg |
Phase shift for the Fermi Chopper approximation |
0 |
|
reflect |
str |
Reflectivity file name. Format <q(Å-1) R(0-1)> |
"NULL" |
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Component source code found in file Guide_gravity.comp.