The `Guide_gravity` Component

Neutron straight guide with gravity. Can be channeled and focusing. Waviness may be specified, as well as side chamfers (on substrate).

Identification

Site:
Author: Emmanuel Farhi
Origin: ILL (France).
Date: Aug 03 2001

Description

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[Angs-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

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. 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	AA-1	Critical scattering vector	0.0218
alpha	AA	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	AA-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/s2	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	"NULL"

AT (	,	,		) RELATIVE
ROTATED (	,	,		) RELATIVE

The Guide_gravity Component

Identification

Description

Input parameters

Links

The `Guide_gravity` Component