Add instrument examples of SPODI (FRMII) powder diffractometer

[kinetik161]

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Here are two models of the SPODI (FRMII) powder diffractometer:

• a model using a simplified banana detector: FRMII_SPODI
• a model representing the real multi-detector geometry: FRMII_SPODI_MULTI.instr

I have not added anything else except for instrument files themselves and documentation README files. @willend , could you please check whether the models in their current form are sufficient?

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Development OS / boundary conditions

Developed and tested on Windows

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PR Checklist for contributing to McStas/McXtrace

For a coherent and useful contribution to McStas/McXtrace, please fill in relevant parts of the checklist:

• My contribution includes a new instrument file

  • I have used the mcdoc utility and rendered a reasonable documentation page for the instrument (please attach as screenshot in comments!)
  • I have ensured that basic use of the instrument is OK (e.g. it compiles?)
  • ... and provided reasonable default parameters in that instrument that produce reasonable output
  • ... and maybe even added a %Example: line to describe expected behaviour
  • I have used the mcrun --c-lint "linter" and followed advice to remove most / all warnings that are raised
  • My new instrument is added within the examples hierarchy in a folder in the style of examples/ESS/New_stuff/New_stuff.instr
  • My new instrument has a new, unique filename, not clashing with existing example instruments

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[willend]

@kinetik161 yes will have a look as soon as time allows. :-)

[willend]

@kinetik161 rebased to include various upstream tool / ci changes

[willend]

@kinetik161 I think this looks like good work - thanks for contributing!

Only minor things left to do:

1. Include an %Example: line (at minimum in the simple variant where e.g. theta_narrow or theta_full output is a reasonable single-monitor target).

• An easy way to get this information is to run with -y parameter defaults and grep for the detector output, e.g. mcrun -c --mpi=auto FRMII_SPODI.instr -y -n1e8 | grep theta_full - I got this line:
  Detector: theta_full_I=31699.3 theta_full_ERR=38.2526 theta_full_N=3.60193e+06 "theta_full.dat"
• (double-check with a few simulations of varying statistics, to check the stability of the value - do an average.)

2. I would probably add a SPLIT on the mono also - the default of x10 should be fine.
3. Please also run the linter. :-) (Time-consuming, may not show anything in your case and a little annoying - but may provide useful information/things to fix.)

[kinetik161]

Thanks for the review and recommendations.

1. I have added an %Example for the simplified version using values averaged from runs with NCOUNTS of 1e8. Should one specify that explicitly in the %Example with -n1e8? With lower counts, the value varies a bit noticeably due to the long simulation path.

2. Thank you, with split trajectories on the monochromator, the values look much more reasonable at the standard 1e6. I have added that for both models.

3. I can confirm that the linter (mcrun --c-lint) passed without any warnings, and that it is extremely slow :)

There is a warning at the generation stage, though I suppose it is more general rather than related specifically to the instrument:

WARNING:
 The parameter format of sample_holder is initialized
 using a static {,,,} vector.
  -> Such static vectors support literal numbers ONLY.
  -> Any vector use of variables or defines must happen via a
     DECLARE/INITIALIZE pointer.