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     
Christian Carbogno   
and Helmut Schober   

%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

The FermiChopper_ILL Component

Identification

Description

Input parameters

Links

The `FermiChopper_ILL` Component