The `FermiChopper_ILL` Component

Fermi Chopper with rotating frame.

Identification

Author: M. Poehlmann, C. Carbogno, H. Schober, E. Farhi
Origin: ILL Grenoble / TU Muenchen
Date: May 2002
Version: 1.3
Modification history:
- K.Lieutenant, June 2005: added phase parameter. Comp validation.

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 'width'
of the full package or the width 'w' of each single slit. The other parameter
is calculated by: width = Nslit*w.
The chopper needs a default velocity to calculate the initial value for an
iterative calculation of TOF values. This can be specified by its velocity,
energy, wavelength or wavevector.

Example:
FermiChopper_ILL(phase=-50.0, rad=0.04, nu=100,
  ymin=-0.04, ymax=0.04, w=0.00022475, Nslit=200.0, R0=0.0,
  Qc=0.02176, alpham=2.33, m=0.0, Vi=1000,  slit=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

WARNING: This is a contributed Component.

Input parameters

Parameters in boldface are required; the others are optional.

Name	Unit	Description	Default
filename	str	optional file name to write component statistics (debuging)	0
phase	deg	chopper phase at t=0	0
rad	m	chopper cylinder radius	0.04
nu	Hz	chopper frequency	100
ymin	m	lower y bound of cylinder	-0.04
ymax	m	upper y bound of cylinder	0.04
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
alpham	AA	slope of reflectivity	2.33
m	1	m-value of material. Zero means completely absorbing.	0.0
Wi	AA-1	width of supermirror cut-off	2e-3
Vi	m/s	velocity of prototype neutron. Use 0 for automatic mode	0
slit	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
Ei	meV	optional mean energy of prototype neutron	0
lambda	Angs	optional mean wavelength of prototype neutron	0
Ki	Angs-1	optional mean wavevector of prototype neutron	0
width	m	optional total width of slit package	0

Output parameters

Name	Unit	Description	Default
FCVars	-	structure containing many neutron counters for the data in 'filename', mean velocities, angular frequency of the chopper etc.

The FermiChopper_ILL Component

Identification

Description

Input parameters

Output parameters

Links

The `FermiChopper_ILL` Component