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

# The `Guide_gravity` Component

Neutron 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: 1.15
- 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 guide tube centered on the Z axis. The entrance lies
    in the X-Y plane. Gravitation applies also when reaching the guide input
    window. The guide can be channeled (k,d 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.
    The guide section may be splitted into nelements equivalent parts of length
    l/nelements. Chamfers do apply in between these parts.
    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)

    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) [1] (k-1 vertical dividing walls) | 1
d | m | Thicxkness of subdividing walls [0] | 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 (kh-1 horizontal dividing walls) this enables to have k*kh rectangular channels | -1
kh |  |  | 1
G |  |  | -9.81
wavy |  |  | 0
wavy_z |  |  | 0
wavy_tb |  |  | 0
wavy_lr |  |  | 0
chamfers |  |  | 0
chamfers_z |  |  | 0
chamfers_lr |  |  | 0
chamfers_tb |  |  | 0
nelements |  |  | 1

## Output parameters

Name | Unit | Description | Default
--- | --- | --- | ---
GVars | 1 | internal variables 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 ]