[mcstas-users] curved guide

[Peter Willendrup]

Hi Peter,


I believe the situation is close to what you sketched - apart from the availability of Guide_four_side from PSI (and its even more complex siblings with 2 or 10 layers), which does however have a slightly complex interface to master. - Comes with an example instrument though…


Otherwise, as I understand the problem, the easiest alternatives would indeed be to either

1) Modify Guide_gravity with curvature (non-trivial if not to be implemented like Bender)

2) Modify Guide_curved with multiple, independent reflectivities (and live with the fact that this then doesn’t include gravity)


There is also a further approximative solution to use Elliptical_guide_gravity (which adds a transverse component to gravity to implement the curvature), but this has a linear appearance in mcdisplay as well…



Cheers,

Peter


> On 18 Jul 2019, at 14.12, Peter Link <Peter.Link at frm2.tum.de> wrote:
> 
> Hi Christoph,
> 
> this is just the point: I'm producing real neutron guide elements, which are "truly curved" 2m long pieces of glass, which are really bent on radii between 30m and several thousands of m. Usually I use the same approx. as you, but I'm thinking about a more realistic way to simulate my guides.
> 
> Best regards
> 
> Peter
> 
> Am 18.07.2019 um 14:07 schrieb 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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>> mcstas-users at mcstas.org
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> 
> -- 
> 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
> 
> _______________________________________________
> mcstas-users mailing list
> mcstas-users at mcstas.org
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Best regards / Mvh

Peter Willendrup
pwillendrup at gmail.com



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