The `Guide_gravity_shieldinglogger` Component

to the m-value of the coating or to -1 if missed the guide opening 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	1.0
W		(AA-1) Width of supermirror cut-off	0.003
nslit		(1) Number of vertical channels in the guide (>= 1)	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).	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 [q(Angs-1) R(0-1)]	"NULL"

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

The Guide_gravity_shieldinglogger Component

Identification

Description

Input parameters

Links

The `Guide_gravity_shieldinglogger` Component