[Nexus] How to model a grating monochromator?

[Pete R Jemian]

Gerd:

Definitely you want to stay with NXmonochromator since this device is a 
wavelength filter.  NXmonochromator's doc says "This is a base class for 
everything which selects a wavelength or energy, be it a monochromator 
crystal, a velocity selector, a undulator or whatever."

NXgrating as a base class seems to be the right idea.  What does its 
content look like?

The multilayer mirror is used as a monochromator for wider bandpass.

Your suggestions here would add this to NXmonochromator.nxdl.xml:
     <group type="NXgrating"><doc>Use as many as necessary/doc></group>
     <group type="NXmirror"><doc>Use as many as necessary/doc></group>

This is reasonable in comparison with NXcrystal and NXvelocity_selector 
as other possible subgroups.

Responses to another question on your URL:

Q: "What is the difference between NXfilter and NXattenuator?"
R: intended usage seems to be the biggest difference.
   NXattentuator is a simple model of a substance that reduces beam 
intensity.
   NXfilter is a more complicated model of an object that acts as a 
bandpass filter.  It provides for specification of crystal structure.

   IMHO: When in doubt, you probably want to use NXfilter.  Leave 
NXattenuator for when you are certain it fits and NXfilter is too limited.


Q: "How to model a standard motor? NXpositioner is according to M. 
Koennecke no to be used!"
R: The discussion is not settled.  NXpositioner was the proposition to 
model a standard motor.  It has been augmented in the usual method of 
committees and its clear function may have beceome obscured.

Thanks,
    Pete




On 11/26/2010 02:47 AM, Wellenreuther, Gerd wrote:
> Dear all,
>
> I am right now trying to assemble the most important NeXus-building
> blocks for a virtual all-purpose SR-beamline
> (https://hdri-sdf.desy.de/index.php/SR_Example). I wonder how to
> properly represent a monochromator which is using gratings instead of
> crystals. What about introducing an NXgrating baseclass, and allow them
> to be used instead of NXcrystal in NXmonochromator?
>
> And while we are thinking about this, what about multilayers? They are
> modeled using NXmirror, right? Could they be an option in
> NXmonochromator, too?
>
> Cheers, Gerd