Author: M. Poehlmann, C. Carbogno, H. Schober, E. Farhi
Origin: ILL Grenoble / TU Muenchen
Date: May 2002
K.Lieutenant, June 2005: added phase parameter. Comp validation.
EF, Nov 2005: completely rewrote comp.
EF, Oct 2008: fix chopper orientation
EF, Mar 2009: improved intersection algorithm
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. The slit package may be made curved and use
FermiChopper(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)
Apr 2005: extensive external test, most problems solved (cf. 'Bugs')
Validated by: K. Lieutenant, E. Farhi
May 2017: Issues in use of supermirror slit packages are being investigated. Is NOT solved for McStas 2.4. The component works correctly when not using supermirrors.
We suggest to instead use Guide_channeled with the rotate/derotate option shown in the test instrument Test_Fermi.instr.
no absorbing blade width used
Parameters in boldface are required;
the others are optional.
chopper phase at t=0
chopper cylinder radius
chopper frequency. Omega=2*PI*nu in rad/s, nu*60 in rpm. Positive value corresponds to a counter-clockwise rotation around y.
width of one chopper slit
number of chopper slits
critical scattering vector
slope of reflectivity
m-value of material. Zero means completely absorbing.
width of supermirror cut-off
channel length of the Fermi chopper
efficiency = transmission x fraction of transparent material
set time to zero: 0=no, 1=once per half cycle, 2=auto adjust phase
optional total width of slit package
set to 1,2 or 3 gives debugging information
height of slit package
Curvature of slits (1/radius of curvature).
sets phase so that transmision is centered on 'delay'