[neutron-mc] McStas Polarisation details

[Klaus Lieutenant]

Hi Rob,

I still think the best way is to treat the neutrons in the local 
co-ordinate system of a component and let the McStas kernel perform the 
transformation (of the neutron co-ordinates) to the following 
components, i.e. not to perform any additional transformation due to 
position or orientation of the component. This works fine with position 
and velocity; and (without looking into details) I do not see why it 
should fail with the spin.
By the way, I am very interested in your work, because I will probably 
also write components for polarised neutrons in the near future. Maybe 
we should meet when I am at ISIS end of September.

Klaus



Dalgliesh, RM (Robert) wrote:

>Hi Klaus,
>It's exactly this sort of situation I'm trying to imagine. On CRISP (at ISIS) we make use of a horizontal polarisation direction and then analyse in the vertical so that we can probe off specular scattering from a horizontal sample. For this I would write a spin rotator component to do the same job as the physical device. This is very trivial. The problem I have with allowing the spin vector to be rotated is with what happens as more polarising components are added and if they are rotated with respect to one another or positioned absolutley. In the long run this is likely to get very messy.
>I thought that another alternative to do this would be to apply the inverse of ROT _A_CURRENT_COMP, as Peter originally suggested, in the component but as ROT _A_CURRENT_COMP is cummulative it would depend on where you polarised your beam as to what happens.
> 
>Rob
>  
>