[mcstas-users] Virtual source with fixed-m divergence

[Thierry Bigault]

Dear McStas,

Here is my problem:
I would like to simulate the exit of a cold neutron guide with a source. 
The aim is to concentrate on the instrument optics, without having to 
calculate all the guide from the reactor.
A simplified and quite general description of a guide exit is a beam 
with a fixed "m-value" divergence: for a given wavelength, the width of 
the angular divergence (either box-type, Gaussian or whatever) is 
essentially proportional to the m-value of the guide coating and to the 
wavelength.
If the guide has different supermirror coatings on horizontal and on 
vertical faces, this leads to different angular widths.
I assume the beam characteristics does not depend on the position at the 
guide exit in this approach.
My question is : what is the simplest way to simulate such a secondary 
(or virtual) source in McStas ? I only found components where the 
angular width is geometrically fixed (in degrees), therefore 
wavelength-independent.
Ideally I would also like to include a non-flat wavelength intensity 
distribution, but this can probably be done by adding a Filter_gen after 
the source.
I am thinking of making several calculations at different wavelengths, 
but if anyone knows a all-in-one solution I am interested.

Thierry




-- 
Logo ILL <https://www.ill.eu/> 	
Dr. Thierry BIGAULT
Research Engineer
Multlayer Neutron Optics
*Institut Max von Laue - Paul Langevin (ILL)*
71, avenue des Martyrs - CS 20156
38042 Grenoble cedex 9 - France
+33 (0)4 76 20 76 95
bigault at ill.eu

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