[ Identification | Description | Input parameters | Output 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).

## Identification

- Author: Emmanuel Farhi
- Origin: ILL (France).
- Date: Aug 03 2001
- Version: 1.24
- Modification history:
  - E. Farhi, from Gravity_guide by K. Lefmann (buggy).
  - E. Farhi, focusing channels are now ok (Sept 4th, 2001).
  - E. Farhi, 2D channel array. Correct focus bug (Dec 14th 2002)
  - E. Farhi, Waviness+chamfers+nelements (Aug 19th 2003)

## 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 (k,d,kh 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.
    For details on the geometry calculation see the description in the McStas
    reference manual.

    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, k=1, d=0.0005)

    %VALIDATION
    May 2005: extensive internal test, all problems solved
    Validated by: K. Lieutenant

    Example values: m=4 Qc=0.02 W=1/300 alpha=6.49 R0=1

## 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 |
h2 | m | Height at the guide exit |
l | m | length of guide |
R0 | 1 | Low-angle reflectivity | 0.99
Qc | AA-1 | Critical scattering vector | 0.0219
alpha | AA | Slope of reflectivity | 6.07
m | 1 | m-value of material. Zero means completely absorbing. | 1.0
W | AA-1 | Width of supermirror cut-off | 0.003
k | 1 | Number of vertical channels in the guide (>= 1) (k-1 vertical dividing walls). | 1
d | m | Thicxkness 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
kh | 1 | Number of horizontal channels in the guide (>= 1). (kh-1 horizontal dividing walls). this enables to have k*kh rectangular channels | 1
G | m/s2 | Gravitation norm. 0 value disables G effects. | 0
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

## Output parameters

Name | Unit | Description | Default
--- | --- | --- | ---
GVars | - | .N_reflection: (1) Array of the cumulated Number of reflections. N_reflection[0] total nb of reflections, N_reflection[1,2,3,4] l/r/t/b reflections, N_reflection[5] total nb neutrons exiting guide, N_reflection[6] total nb neutrons entering guide. |

## Links

- Source code for `Guide_gravity.comp`.

[ Identification | Description | Input parameters | Output parameters | Links ]