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<div class="PlainText">Dear Andrew,<br>
<br>
<br>
Thanks for raising the issue!<br>
<br>
I have had a closer look and also written a small test-instrument myself, see attached. This instrument contains a source that fully illuminates a chopper disk in the time-interval of [0 1]s, and with exposed parameters to set phase, delay, nu etc.
<br>
<br>
I have the following findings:<br>
<br>
1) Looking at the outputs, setting the default input-parameters it does in fact look like the order of rotation is left-handed rather than right-handed, see attached plot1.png, run with a 1Hz chopper<br>
<br>
2) Putting phase to 90 degrees and parking the chopper there (nu=0), it further looks like the geometry as visualised using mcdisplay is opposite to what the resulting simulation output shows, see mcdisplay.png and plot2.png<br>
<br>
<br>
<br>
I will file a us a GitHub issue so that we remember to do something about this, likely the below solution as a number of existing instrument-models use the DiskChopper exactly as it looks today:<br>
<br>
1) Fix the documentation so that it is clear that the default “sign” of rotation is left-handed<br>
<br>
2) Fix mcdisplay so that it reflects what the neutrons will “see” at t=0<br>
<br>
3) Potentially add a sign-parameter to choose the “handedness” <br>
<br>
<br>
Best and thanks for reporting,<br>
Peter<br>
<br>
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<div><img src="cid:c797dbdc-e501-44d5-81ca-f5c579d3efff@win.dtu.dk"> </div>
<div><img src="cid:90b68f6b-918a-4e1d-be66-4257549c305f@win.dtu.dk"> </div>
<div><img src="cid:5f66804a-bc37-432f-aa15-8f259a2b5e85@win.dtu.dk"> </div>
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<br>
> On 11 Jun 2021, at 04.35, Andrew Nelson <andyfaff@gmail.com> wrote:<br>
> <br>
> Dear Markus,<br>
> thank you for the reply. Perhaps naively I would expect the trace to correspond to what happens with the actual simulation.<br>
> <br>
> I have done something along the lines you suggest, see end of email. The TOF monitor is shifted along the +ve x direction, which is to the right when looking from the detector to the source (it'd be roughly where the 'h' label is in fig 6.1)<br>
> <br>
> When nu is positive the TOF monitor has a pulse distribution whose offset is shifted to positive times. I think this means that the midpoint of the disk window has already crossed the y-axis before it gets to the monitor. This must mean that the direction
of rotation is clockwise when looking along z from +ve to -ve.<br>
> <br>
> When nu is negative the TOF monitor has a pulse distribution whose offset is shifted to negative times. This must mean that the direction of rotation is anticlockwise when looking along z from +ve to -ve.<br>
> <br>
> Is this assessment correct?<br>
> <br>
> If so, then this is not what I expect from a right hand coordinate system. The direction of rotation from this concept experiment is the opposite of what's displayed in figure 6.1 of the component manual.<br>
> <br>
> <br>
> <br>
> <br>
> ===============================================================<br>
> DEFINE INSTRUMENT template_simple(Par1=1)<br>
> <br>
> DECLARE<br>
> %{<br>
> %}<br>
> <br>
> INITIALIZE<br>
> %{<br>
> %}<br>
> <br>
> TRACE<br>
> <br>
> COMPONENT origin = Progress_bar()<br>
> AT (0, 0, 0) RELATIVE ABSOLUTE<br>
> <br>
> // insert components here (e.g. Insert -> Source -> ...)<br>
> COMPONENT source_div = Source_div(<br>
> xwidth=0.02, <br>
> yheight=0.05, <br>
> focus_aw=1, <br>
> focus_ah=1, <br>
> lambda0=2.8, <br>
> dlambda=0.1)<br>
> AT (0, 0, 0) RELATIVE PREVIOUS<br>
> <br>
> COMPONENT diskchopper = DiskChopper(<br>
> theta_0=5, <br>
> yheight=0.1, <br>
> nu=24,<br>
> isfirst=1)<br>
> AT (0, 0, 0) RELATIVE PREVIOUS<br>
> <br>
> COMPONENT mon = TOF_monitor(<br>
> filename="mon", <br>
> xmin=0.005, <br>
> xmax=0.01, <br>
> ymin=-0.025, <br>
> ymax=0.025,<br>
> tmin=-500,<br>
> tmax=500,<br>
> restore_neutron=1)<br>
> AT (0, 0, 0) RELATIVE PREVIOUS<br>
> <br>
> FINALLY<br>
> %{<br>
> %}<br>
> <br>
> END<br>
> _______________________________________________<br>
> mcstas-users mailing list<br>
> mcstas-users@mcstas.org<br>
> <a href="https://mailman2.mcstas.org/mailman/listinfo/mcstas-users">https://mailman2.mcstas.org/mailman/listinfo/mcstas-users</a><br>
<br>
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