[ Identification | Description | Input parameters | Links ]

The FermiChopper 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. The slit package may be made curved and use
super-mirror coating.

Example:
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)

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

limitations:
no absorbing blade width used

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. Omega=2*PI*nu in rad/s, nu*60 in rpm. Positive value corresponds to a counter-clockwise rotation around y.	100
w	m	width of one chopper slit	0.00022475
nslit	1	number of chopper slits	200
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, 2=auto adjust phase	0
xwidth	m	optional total width of slit package	0
verbose	1	set to 1,2 or 3 gives debugging information	0
yheight	m	height of slit package	0.08
curvature	m-1	Curvature of slits (1/radius of curvature).	0
delay	s	sets phase so that transmision is centered on 'delay'	0

AT (	,	,		) RELATIVE		Generate
ROTATED (	,	,		) RELATIVE

Links

• Source code for FermiChopper.comp.
• Vitess_ChopperFermi component by
• G. Zsigmond, imported from Vitess by K. Lieutenant.

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[ Identification | Description | Input parameters | Links ]

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

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Last Modified: Tuesday, 17-Sep-2024 05:31:14 CEST