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McStas: DiskChopper Component

[ Identification | Description | Input parameters | Output parameters | Links ]

The DiskChopper Component

Based on Chopper (Philipp Bernhardt), Jitter and beamstop from work by Kaspar Hewitt Klenoe (jan 2006), adjustments by Rob Bewey (march 2006)


  • Author: Peter Willendrup
  • Origin: Risoe
  • Date: March 9 2006
  • Version:(Unknown)


Models a disc chopper with nslit identical slits, which are symmetrically distributed
on the disc. At time t=0, the centre of the first slit opening will be situated at the
vertical axis when phase=0, assuming the chopper centre of rotation is placed BELOW the beam axis.
If you want to place the chopper ABOVE the beam axis, please use a 180 degree rotation around Z 
(otherwise unexpected beam splitting can occur in combination with the isfirst=1 setting, see
 related bug on GitHub)

For more complicated gemometries, see component manual example of DiskChopper GROUPing.

If the chopper is the 1st chopper of the instrument, it sets t time with phase
- Only relevant for when using continuous source modules.

Example: DiskChopper(radius=0.2, theta_0=10, nu=41.7, nslit=3, delay=0, isfirst=1) First chopper
         DiskChopper(radius=0.2, theta_0=10, nu=41.7, nslit=3, delay=0, isfirst=0)

Input parameters

Parameters in boldface are required; the others are optional.
Name Unit Description Default
theta_0 deg Angular width of the slits. 0
radius m Radius of the disc 0.5
yheight m Slit height (if = 0, equal to radius). Auto centering of beam at half height.  
nu algebraic sign defines the direction of rotation [Hz] Frequency of the Chopper, omega=2*PI*nu  
nslit 1 Number of slits, regularly arranged around the disk 3
jitter s Jitter in the time phase 0
delay s Time 'delay' 0
isfirst it then spreads the neutron time distribution [0/1] Set it to 1 for the first chopper position in a cw source 0
n_pulse Only if isfirst [1] Number of pulses 1
abs_out 0/1 Absorb neutrons hitting outside of chopper radius? 1
phase overrides delay [deg] Angular 'delay' 0
xwidth m Horizontal slit width opening at beam center 0
verbose 1 Set to 1 to display Disk chopper configuration 0

Output parameters

Name Unit Description Default


[ Identification | Description | Input parameters | Output parameters | Links ]

Generated automatically by McDoc, Peter Willendrup <> / Wed Jan 12 15:13:31 2022

Last Modified: Wednesday, 12-Jan-2022 16:13:31 CET
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