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McStas: FermiChopper_ILL

[ Identification | Description | Input parameters | Links ]

The FermiChopper_ILL Component

Fermi Chopper with rotating frame.


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


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.

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,

Markus Poehlmann     
Christian Carbogno   
and Helmut Schober   

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

no blade width used

- 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.
phasedegchopper phase at t=00
radiusmchopper cylinder radius0.04
nuHzchopper frequency100
yheightmHeight of chopper0.08
wmwidth of one chopper slit0.00022475
nslit1number of chopper slits200.0
R01low-angle reflectivity0.0
QcAA-1critical scattering vector0.02176
alphaAAslope of reflectivity2.33
m1m-value of material. Zero means completely absorbing.0.0
WAA-1width of supermirror cut-off2e-3
lengthmchannel length of the Fermi chopper0.012
eff1efficiency = transmission x fraction of transparent material0.95
zero_time1set time to zero: 0: no 1: once per half cycle0
xwidthmoptional total width of slit package0
verbose1optional flag to display component statistics, use 1 or 3 (debuging)0


[ Identification | Description | Input parameters | Links ]

Generated on 2023-09-19 20:01:36

Last Modified: Wednesday, 03-Jan-2024 19:59:10 CET
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