[mcstas-users] Query in regard to McStas

[FARHI Emmanuel]

Hello Indu, 

Thanks for your message. That's nice if you are now working on the PEARL diffractometer. It was initially designed by Lambert, and McStas helped at this time. I have myself moved away from neutrons in the mean time. 

To start with, I would advice to look at the ILL_D2B and the templateDIFF examples which make use of the Monochromator_curved. This is to check that you can extract a beam at the right angle with a simplified Ge model. 
Then, you may gradually transition to the Single_crystal by looking at the Test_Monochromators. Make sure you can compute the a,b,c vectors for the Example Mono=6 lines there-in. 

The cut itself is only relevant to properly compute the beam attenuation. The reflection itself is independent of the surface orientation, but clearly it is best to cut according to the target reflection. So you may start by using a 'normal' Ge crystal, find the reflection, and then compute a new geometry with the proper cut. The SX component allows to orient the cut in real or reciprocal space. You should have a look at the component manual for these aspects. 

Emmanuel. 


De: "Indu Dhiman" <I.Dhiman at tudelft.nl> 
À: "FARHI Emmanuel" <emmanuel.farhi at synchrotron-soleil.fr> 
Envoyé: Vendredi 16 Août 2024 11:34:51 
Objet: Query in regard to McStas 





Dear Emanuel, 



I hope this email finds you well. To introduce myself, I work as an instrument scientist on the PEARL neutron diffractometer at RID, TU Delft. You may not recollect, we have met twice in ORNL 2018 and a year before in ILL, for a neutron imaging talk you organized. 





I am writing to you with a query I have regarding the PEARL diffractometer. We are planning few upgrades on the instrument and would like to simulate it with the McStas. 



To further elaborate, I am trying build a McStas file for this instrument. For the monochromator I would like to use single_crystal component in McStas. I am trying to use Ge monochromator (Ge. Lau file) to have a wavelength of 1.667 AA-1 for 533 reflections with a take-off angle of 150 deg (2theta). The Ge crystal on PEARL diffractometer is cut such that the normal to the wafer surface is (5 3 3). 

However, I am unable to include the correctly align the monochromator to get this wavelength on to the sample position. I would really appreciate your input on this. I am also attaching all the input files I am using for you reference with this email. 



Really looking forward to your help. 



Thanking you in anticipation 



With best regards 



Indu Dhiman 

-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://mailman2.mcstas.org/pipermail/mcstas-users/attachments/20240816/bdc884c6/attachment-0001.html>