[mcstas-users] introducing an absorber inside a guide

Peter Kjær Willendrup pkwi at fysik.dtu.dk
Tue May 3 09:38:41 CEST 2022

Dear Jean-Francois,

Unfortunately there is no easy way of achieving this using the McStas grammar by itself, so some coding on your behalf is required.

Since we are in the middle of an elliptical guide, my advice would be to split the guide in 2-3 sections:

	• An expanding elliptic section
	• A straight part - where we will place the absorber
	• A focusing elliptic section

The straight part can then either be written as a dedicated component or approximated by putting together “simpler parts”, i.e. perhaps a GROUP of an absorber and a straight guide or depending on your needs, perhaps a guide section with an EXTEND eating away the central part of the beam. If you try with a GROUP my feeling is that you will get the most mileage from putting the absorber “first” in the GROUP and ensure that every “Absorbed” neutron raises a SCATTER.

Best and good luck, contact me off-list if you need further tips,


> On 2 May 2022, at 16.37, Jean-Francois Moulin <jean-francois.moulin at hereon.de> wrote:
> Hello,
> I am trying to simulate a setup (based on elliptic-guide-gravity) where I need to insert an absorber in the middle of the guide.
> Is there a conventional method to achieve this or do I need to modify the code at the component level?
> Any hint appreciated.
> JF
> -- 
> Dr. Jean-François Moulin
> German Engineering Materials Science Centre (GEMS)
> at Heinz Maier-Leibnitz Zentrum (MLZ)
> Helmholtz-Zentrum Hereon
> Lichtenbergstr. 1, 85747 Garching bei München, Germany
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