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[ 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: 1.33
- 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.
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.
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: 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 |
|---|---|---|---|
| reflect | str | Reflectivity file name. Format [q(Angs-1) R(0-1)] | 0 |
| 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 | 0.99 |
| 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 | 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 |
| 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 |
| aleft | 1 | alphpa-value of left vert. mirror | -1 |
| aright | 1 | alphpa-value of right vert. mirror | -1 |
| atop | 1 | alphpa-value of top horz. mirror | -1 |
| abottom | 1 | alphpa-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 |
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. | |
| pTable |
Links
- Source code for
Guide_gravity.comp.
[ Identification | Description | Input parameters | Output parameters | Links ]
Generated automatically by McDoc, Peter Willendrup <peter.willendrup@risoe.dk> / Sat Jul 31 08:37:33 2010
