[mcstas-users] monochromator curvature issue

Peter Link Peter.Link at frm2.tum.de
Thu Aug 27 15:23:07 CEST 2015

Dear Tom,
once you use monochromator_curved.comp in an instrument simulation with 
a "real" divergent beam, you are perfectly right, the simple parallel 
beam relation doen't hold any more. At the time, when I wrote the very 
first version of this comp for the thermal TAS PUMA at FRM II, I 
"calibrated" RH, RV in dependence of A1 and L by scanning RH, RV with a 
monitor at the sample position. The resulting optimal RH(L,A1) and 
RV(L,A1) values were then used for further simulations...
Finally this corresponds somehow the procedure that you carry out on the 
real instrument, when you initialize the monochromator.
Best regards,

Am 21.08.2015 um 10:12 schrieb 陈彦舟:
> Dear all,
> In the simulation of monochromator_curved, the curvatures 
> approximation for parallel beam focusing to distance L with 
> monochromator rotation angle A1 are:
> RV=2*L*sin(DEG2RAD*A1);
> RH=2*L/sin(DEG2RAD*A1);
> However, in reality, the incoming neutron beam has a certain 
> divergence. My question is how  to define the curvatures of the 
> monochromator considering the divergence?
> Best regards,
> Tom
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Dr. Peter Link
Head of Neutron Optics
Heinz Maier-Leibnitz Zentrum (MLZ)
Technische Universität München
Lichtenbergstr. 1
85747 Garching
phone: +49 (0)89 289 14622
fax: +49 (0) 89 289 11694

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