Corelli sample

[HaShuai123]

Dear experts,

I am trying to reproduce the work in the paper "Corelli: Efficient single crystal diffraction with elastic discrimination". https://link.springer.com/article/10.1007/s12043-008-0259-x

But I have trouble to understand how to model the sample. it is said "a powder sample using a harmonic oscillator model with ω0 = 2 meV, including excitations up to the fifth harmonic."

Could you please kindly help me with which sample component is appropriate for this modelling?

Besides, Does the component [StatisticalChopper] work for a pulsed source?

Any help would be appreciated.

Best regards,
Ha Shuai.

[willend]

Dear @HaShuai123,

To my memory Stefan Rosenkranz used a sample model of his own for the Corelli simulations - and this model was never contributed back to McStas. I would try to reach out to Stefan for more information.

I on the other hand believe that the StatisticalChopper was used for exactly the Corelli simulations together with the SNS source model, so yes should work for pulsed source models.

I recommend looking at the Test_StatisticalChopper.instr instrument which uses a simple ToF source implemented using an EXTEND block:

COMPONENT source1 = Source_simple(xwidth=0.026, yheight=0.026,
  lambda0=lambda, dlambda=0.00001,
  focus_xw=0.005, focus_yh=0.05, dist=1.2)
AT (0,0,.001) relative PREVIOUS
EXTEND %{
  t=randpm1()*255/60/1487;
%}

[HaShuai123]

Dear @willend,

Thank you very much for your help.
In case of cannot reach out to Stefan, what sample component and powder samples do you recommend I try to obtain somewhat similar results (have small inelastic scattering peaks near the elastic scattering peaks)?

Best regards,
Ha Shuai.

[willend]

Dear @HaShuai123,

In this case I would consider using the “Tunneling_sample.comp” which has quasi-elastic broadening and “tunneling peaks” (or thinking about it, maybe even Incoherent.comp has these features...)

[HaShuai123]

Dear @willend

Thanks.
I looked at the parameters for the "Incoherent" sample component.
To have this quasielastic scattering, I guess the parameters "f_QE", "gamma", "Etrans", "deltaE" need to be set. What are reasonable numbers for those parameters?

For the "Tunneling_sample", I guess the parameters ""f_QE" and "gamma" need to be set. Is this correct?

Best regards,
Ha Shuai.

[willend]

Hi again @HaShuai123,

Use the mcdoc pages of the components - at best using the mcdoc command in your McStas environment.
(The pages are also on the McStas webpage under http://mcstas.org/download/components/ - but what is found here can differ slightly if you are running a slightly different version)

The instrument example ESS_IN5_reprate.instr uses Tunneling_sample, you may inspire from that also.

Best
Peter

Screenshots below for:
Tunneling_sample:

Incoherent:

[HaShuai123]

Dear @willend

Thank you very much for your kind help.

Best regards,
Ha Shuai

[granrothge]

@HaShuai123 I have used theIsotropicSqw component for these purposes before and it has worked quite well. You would just define constant Energy transfer lines in the input file. It has been awhile since I have used the component so I am not sure I can be of more help.
Best,

Garrett

[willend]

Ah yes @granrothge this is also an option!

For an example @HaShuai123 you can look inside ILL_IN4.instr that 1) writes an .sqw file in INITIALIZE (this one with dirac points in q/E) 2) uses that in simulation of the instr resolution

[HaShuai123]

Dear @granrothge and @willend

Thank you very much for your kind help.
I have some problems with understanding how the IsotropicSqw samples work.
Finally, be able to reproduce a somewhat similar result through Tunneling_sample.

Best wishes,
Ha Shuai