[mcstas-users] curved guide

[Christoph Frommen]

Dear Peter,

I usually try to model curved guides realistically, meaning with a "short section approximation" of individual straight segments each having a certain gap between each other. 
I am following a procedure described in by V.M. Pusenkov et all in "Nucl. Instrum. Meth. A 492 (2002) 105-116".

Below is an example for one segment of a multichannel guide (3 channels)  with 2.5 mm walls in between. You can still have different m coatings since it is a gravity_guide. You could use the COPY statement to generate the necessary number of those segments.

------------------------------------------------------------
*gLength: [m] length of individual guide pieces
*gGap: [m] gap between guide pieces 
*gReflect0: guide reflectivity 
*gQc: [AA-1] critical wave vector 
*gAlpha : [deg] slope of reflectivity curve 
*gW, gH : [m] guide entrance/exit widths/heights  
*R_curv_m : [m] radius of curvature for bent guide section 

component bent_section_1 =  Guide_gravity(w1=gW, w2=gW, h1=gH, h2=gH, l=gLength, 
R0=gReflect0, Qc=gQc, alpha=gAlpha, 
m=2, nslit=3, d=0.0025) at (0, 0, gGap+gLength) 
relative previous rotated (0, gLength/R_curve_m*180.0/PI, 0) relative previous
---------------------------------------------------------------

Maybe someone has a more elegant solution?


Best regards
Christoph

-----Original Message-----
From: mcstas-users <mcstas-users-bounces at mcstas.org> On Behalf Of Peter Link
Sent: 18 July 2019 13:25
To: mcstas-users at mcstas.org
Subject: [mcstas-users] curved guide

Dear friends,

just to avoid some double developpment: to my knowlegde there are the following components or ways to simulate a standard curved neutron guide:

Bender; allows for different reflectivities on top/bottom inside outside; can have multiple channels; but behaves geometrically as straight guide element (mcdisplay, coordinates of subsequent elements)

Guide_curved; only one reflectivity definition for all sides, geometrically correct definition

polygon of Guide_gravity elements; allows for a polygonal approximation only, has numerous options

Having a number of truly curved guides in my simulations I would prefer to have a component, which has the possibilities as it has Bender or Guide_gravity but is a geomentrical correct implementation of truly curved guide. If someone has done this or can tell me where I have overseen it, I would be grateful.

Bets regards

Peter


--
Dr. Peter Link
Leiter Neutronenoptik
Technische Universität München
Heinz Maier-Leibnitz Zentrum (MLZ)

Lichtenbergstr. 1
85747 Garching

Tel.: +49 (0)89 289 14622
Fax: +49 (0) 89 289 11694

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