[Nexus] How to model a grating monochromator?

[Wellenreuther, Gerd]

Hi Pete,

thanks for answering!

About the grating: I can ask Jens Viefhaus, who will be using gratings 
for his beamline at PETRA III, to help me compiling a list of parameters 
required to describe a grating used in monochromators. Or maybe there is 
some expert from Bessy / HZB who could do this as well or better?

About the motors/NXpositioner: I think we definitely need a defined way 
of saving not only the position of a motor, but all its settings ( think 
of soft- and hard-limits, slew_rate, acceleration, stepping_mode, 
currents, home, conversion, encoders & calibration, units, ...) . This 
should be handled by a base class, IMHO.

What is not clear to me yet is given a device like a crystal in a 
monochromator, and given a couple of devices like motors moving/tilting 
such a crystal - how should I define what a certain motor is actually 
doing? Just trying to deduce the motors function from a name sounds 
dangerous ...

Cheers, Gerd

On 30.11.2010 23:07, Pete R Jemian wrote:
>
> 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

-- 
Dr. Gerd Wellenreuther
beamline scientist P06 "Hard X-Ray Micro/Nano-Probe"
Petra III project
HASYLAB at DESY
Notkestr. 85
22607 Hamburg

Tel.: + 49 40 8998 5701