McStas logo McStas - A neutron ray-trace simulation package ILL; PSI; ESS Niels Bohr Institute DTU Physics NEXMAP


About McStas
 Conditions of use
 Project funding

 Other Downloads (share)

Mailing list

Search web/mailinglist

 Wiki (GitHub)
 McStas manual


Report bugs (GitHub)

Code-repository (GitHub)

McStas: Guide_gravity

[ Identification | Description | Input parameters | Links ]

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).



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

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)

May 2005: extensive internal test, all problems solved
Validated by: nslit. Lieutenant

Input parameters

Parameters in boldface are required; the others are optional.
w1mWidth at the guide entry
h1mHeight at the guide entry
w2mWidth at the guide exit. If 0, use w1.0
h2mHeight at the guide exit. If 0, use h1.0
lmlength of guide
R01Low-angle reflectivity0.995
QcAA-1Critical scattering vector0.0218
alphaAASlope of reflectivity4.38
m1m-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 Si1.0
WAA-1Width of supermirror cut-off0.003
nslit1Number of vertical channels in the guide (>= 1) (nslit-1 vertical dividing walls).1
dmThickness of subdividing walls0.0005
mleft1m-value of material for left. vert. mirror-1
mright1m-value of material for right. vert. mirror-1
mtop1m-value of material for top. horz. mirror-1
mbottom1m-value of material for bottom. horz. mirror-1
nhslit1Number of horizontal channels in the guide (>= 1). (nhslit-1 horizontal dividing walls). this enables to have nslit*nhslit rectangular channels1
Gm/s2Gravitation norm. 0 value disables G effects.0
aleft1alpha-value of left vert. mirror-1
aright1alpha-value of right vert. mirror-1
atop1alpha-value of top horz. mirror-1
abottom1alpha-value of left horz. mirror-1
wavydegGlobal guide waviness0
wavy_zdegPartial waviness along propagation axis0
wavy_tbdegPartial waviness in transverse direction for top/bottom mirrors0
wavy_lrdegPartial waviness in transverse direction for left/right mirrors0
chamfersmGlobal chamfers specifications (in/out/mirror sides).0
chamfers_zmInput and output chamfers0
chamfers_lrmChamfers on left/right mirror sides0
chamfers_tbmChamfers on top/bottom mirror sides0
nelements1Number of sections in the guide (length l/nelements).1
nuHzRotation frequency (round/s) for Fermi Chopper approximation0
phasedegPhase shift for the Fermi Chopper approximation0
reflectstrReflectivity file name. Format "NULL"


[ Identification | Description | Input parameters | Links ]

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

Last Modified: Tuesday, 16-Apr-2024 20:05:20 CEST
Search website mailinglist archive GitHub repos