[mcstas-users] Disk chopper angular definitions

[Andrew Nelson]

Dear Markus,
thank you for the reply. Perhaps naively I would expect the trace to
correspond to what happens with the actual simulation.

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)

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.

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.

Is this assessment correct?

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.




===============================================================
DEFINE INSTRUMENT template_simple(Par1=1)

DECLARE
%{
%}

INITIALIZE
%{
%}

TRACE

COMPONENT origin = Progress_bar()
AT (0, 0, 0) RELATIVE ABSOLUTE

// insert components here (e.g. Insert -> Source -> ...)
COMPONENT source_div = Source_div(
    xwidth=0.02,
    yheight=0.05,
    focus_aw=1,
    focus_ah=1,
    lambda0=2.8,
    dlambda=0.1)
AT (0, 0, 0) RELATIVE PREVIOUS

COMPONENT diskchopper = DiskChopper(
    theta_0=5,
    yheight=0.1,
    nu=24,
isfirst=1)
AT (0, 0, 0) RELATIVE PREVIOUS

COMPONENT mon = TOF_monitor(
    filename="mon",
    xmin=0.005,
    xmax=0.01,
    ymin=-0.025,
    ymax=0.025,
    tmin=-500,
    tmax=500,
restore_neutron=1)
AT (0, 0, 0) RELATIVE PREVIOUS

FINALLY
%{
%}

END
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