[ Identification | Description | Input parameters | Links ]

# The `Guide_gravity_psd` 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_psd(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: K. Lieutenant

## Input parameters

Parameters in boldface are required; the others are optional.

Name | Unit | Description | Default |
nxpsd | 1 | Number of bins in the built-in mirror parallel monitors |  |
filenameT | str | Filename for top-mirror-monitor |  |
filenameB | str | Filename for bottom-mirror-monitor |  |
filenameL | str | Filename for left-mirror-monitor |  |
filenameR | str | Filename for right-mirror-monitor |  |
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) (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 q(Angs-1) R(0-1) | "NULL" |

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

## Links

- Source code for `Guide_gravity_psd.comp`.

[ Identification | Description | Input parameters | Links ]