[ Identification | Description | Input parameters | Links ]

# The `FermiChopper_ILL` Component

Fermi Chopper with rotating frame.

## Identification

- Site:
- Author: M. Poehlmann, C. Carbogno, H. Schober, E. Farhi
- Origin: ILL Grenoble / TU Muenchen
- Date: May 2002

## Description

    Models a Fermi chopper with optional supermirror coated blades
    supermirror facilities may be disabled by setting m = 0, R0=0
    Slit packages are straight. Chopper slits are separated by an infinitely
    thin absorbing material. The effective transmission (resulting from fraction
    of the transparent material and its transmission) may be specified.
    The chopper slit package width may be specified through the total width 'xwidth'
    of the full package or the width 'w' of each single slit. The other parameter
    is calculated by: xwidth = nslit*w.

    Example:
    FermiChopper_ILL(phase=-50.0, radius=0.04, nu=100,
    yheight=0.08, w=0.00022475, nslit=200.0, R0=0.0,
    Qc=0.02176, alpha=2.33, m=0.0, length=0.012, eff=0.95,
    zero_time=0)

    Markus Poehlmann     <Markus.Poehlmann@ph.tum.de>
    Christian Carbogno   <carbogno@ph.tum.de>
    and Helmut Schober   <schober@ill.fr>

    %VALIDATION
    Apr 2005: extensive external test, most problems solved (cf. 'Bugs')
    Validated by: K. Lieutenant

    limitations:
    no blade width used

    %BUGS
    - overestimates peak width for long wavelengths
    - does not give the right pulse position, shape and width for slit widths below 0.1 mm
    - fails sometimes when using MPI

## Input parameters

Parameters in boldface are required; the others are optional.

Name | Unit | Description | Default |
phase | deg | chopper phase at t=0 | 0 |
radius | m | chopper cylinder radius | 0.04 |
nu | Hz | chopper frequency | 100 |
yheight | m | Height of chopper | 0.08 |
w | m | width of one chopper slit | 0.00022475 |
nslit | 1 | number of chopper slits | 200.0 |
R0 | 1 | low-angle reflectivity | 0.0 |
Qc | AA-1 | critical scattering vector | 0.02176 |
alpha | AA | slope of reflectivity | 2.33 |
m | 1 | m-value of material. Zero means completely absorbing. | 0.0 |
W | AA-1 | width of supermirror cut-off | 2e-3 |
length | m | channel length of the Fermi chopper | 0.012 |
eff | 1 | efficiency = transmission x fraction of transparent material | 0.95 |
zero_time | 1 | set time to zero: 0: no 1: once per half cycle | 0 |
xwidth | m | optional total width of slit package | 0 |
verbose | 1 | optional flag to display component statistics, use 1 or 3 (debuging) | 0 |

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

## Links

- Source code for `FermiChopper_ILL.comp`.

[ Identification | Description | Input parameters | Links ]