[NeXus-committee] Proposal for NXcrystal and NXmonochromator

Tue Mar 10 11:13:04 GMT 2015

Hi Ben
  extending NXmonochromator for soft x-rays is definitely a good idea. 
However, instead of using all this funny fields I would rather use
Tobias's "features"-feature and define new class NXgrating. 
Then we could have three NXmonochromator related features
1.) NXmonochromator for Neutrons
    whatever is required here - I have no idea about Neutrons 
2.) NXmonochromator for hard x-rays
    NXmonochromator must comprise NXcrystal, type, etc. 
3.) NXmonochromator for soft x-rays
    NXmonochromator must comprise NXgrating, NXslit, etc.

One could think about this as an application definition restricted 
to NXmonochromator ;)


regards
  Eugen


On Tue, 2015-03-10 at 11:54 +0100, Benjamin Watts wrote:
> Hi Eugen & Pete,
>    If you want to move the "usage" field into NXmonochromator, then
> maybe we should rethink NXmonochromator and consider a larger
> overhaul. We currently have the "crystal" and "velocity_selector" as
> optional fields for hard X-rays and neutron, respectively, and I want
> to add "grating" to that set of optional fields for the soft X-ray
> case. For soft X-rays, the situation is actually even more complicated
> as the geometry set by entrance and exit slits are also a fundamental
> part of the monochromator (and the entrance slit is also optional,
> since some beamlines simply consider the source size and position
> stable and small enough).
> Can you think of a better way to achieve all this? One option would be
> to set it up so that one looks at the "usage" field first and then
> uses its value to decide which optional fields to looks for next. This
> would mean including values such as "grating" and "velocity_selector"
> in the list of possibilities for the "usage" field, which would then
> make the name "type" more appropriate.
> 
> Cheers,
> Ben
> 
> 
> On 09/03/15 21:41, Eugen Wintersberger wrote:
> 
> > > The choice of Bragg or Laue orientation is important when calculating 
> > > the rocking curve profile, whether or not the crystal is used as part of 
> > > a monochromator.
> > I entirely agree with you here. However, this is a particular use case
> > for a crystal in connection with a monochromator. Thus, at least in my
> > opinion, the "usage" field belongs to NXmonochromator.
> > 
> > > On 03/09/2015 03:14 PM, Eugen Wintersberger wrote:
> > > > Hi Pete
> > > > 
> > > > On Sun, 2015-03-08 at 11:48 -0500, Pete Jemian wrote:
> > > > > Eugen:
> > > > > 
> > > > > You propose to:
> > > > > * rename "usage" field to "type"
> > > > I propose to remove the "usage" field entirely from NXcrystal.
> > > > 
> > > > > * add "channel_cut" as another possible value
> > > > And I propose to add a "type" field to NXmonochromator. The possible
> > > > values for "type" could be "Laue", "Bragg", "Pseudo Channel Cut", and
> > > > "Channel Cut". Or something in this way.
> > > > 
> > > > > As I said before, "channel_cut" is not an alternative to "Bragg" or
> > > > > "Laue" in its description of crystal orientation.  Most channel cut
> > > > > crystals use Bragg orientation.  I suggest a new field could be added to
> > > > > describe "channel_cut".  Another similar term could be
> > > > > "pseudo_channel_cut" which describes the crystal arrangement of most
> > > > > synchrotron X-ray monochromators.
> > > > This would be the "type" field for NXmonochromator. It should identify
> > > > what type of mono we talk about.
> > > > 
> > > > > Like many things in NeXus, the field name "usage" does not seem to fit
> > > > > so well, as you point out.
> > > > > 
> > > > > Rather than disrupt the historical use of the "usage" field in NeXus
> > > > > data files and however many data files have been written with this
> > > > > field, would it be acceptable to improve the documentation for the
> > > > > "usage" field?
> > > > In the best case I would declare it as deprecated. At least from my
> > > > point of view NXcrystal describes a crystal and not its particular
> > > > application. But we can leave it there for compatibility reasons and
> > > > declare it as deprecated.
> > > > 
> > > > I am not sure if, what I propose, is really the best approach. But for
> > > > the time being I have no better idea how to deal with the situation.
> > > > 
> > > > regards
> > > >    Eugen
> > > > 
> > > > 
> > > > > Pete
> > > > > 
> > > > > On 3/8/2015 10:56 AM, Eugen Wintersberger wrote:
> > > > > > Hi folks
> > > > > >     as a result of the recent discussion I would like to propose the
> > > > > > following changes to NXcrystal:
> > > > > > 
> > > > > > remove the "usage" field from NXcrystal
> > > > > > 
> > > > > > It makes no sense there as the way the crystal is used in a particular
> > > > > > application is entirely unimportant for the particular crystal itself.
> > > > > > 
> > > > > > 
> > > > > > Furthermore I would like to suggest the following change to
> > > > > > NXmonochromator
> > > > > > 
> > > > > > add a "type" field to NXmonochromator
> > > > > > 
> > > > > > This field should basically hold the values of "usage" from the current
> > > > > > NXcrystal class. I would also suggest to have an additional possible
> > > > > > value "channel_cut" available for this field.
> > > > > > 
> > > > > > Best regards
> > > > > > Eugen
> > > > > > 
> > > _______________________________________________
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> > > NeXus-committee at nexusformat.org
> > > http://lists.nexusformat.org/mailman/listinfo/nexus-committee
> > 
> > 
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DI. Dr. Eugen Wintersberger         
                                    
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DESY                    
Notkestrasse 85                       
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E-Mail: eugen.wintersberger at desy.de
Telefon: +49-40-8998-1917          
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