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Question problem with G4Polycone in fresnel lens 

Forum: Geometry
Date: 23 Jul, 2013
From: Michael Eichler <Michael Eichler>

Dear Experts,

i am having a problem in building a fresnel lens with Geant4. The fresnel lens is consisting of grooves that are G4Polycones with a specific "profile". The replication of the Polycones is done by G4PVParameterised, because the profile shape has to be modified from groove to groove.

If i shoot photons at the lens, it seems, that for every photon all grooves are calculated again.

The problem is, that for some "adjustments" of the groove shape, the photons just pass through the grooves without doing a step there - but i can see the whole lens with all grooves in the geometry viewer.

I have done geometry tests and surface-check=true for all placed volumes and the parametrised ones and everything is OK.

If i output the shape parameters of the grooves in the parametrisation function, i can see the grooves (for example number 0-200) being calculated for every photon. If i adjust a groove-profile that leads to the described problem, i can see in the output, that the calculation of the grooves for every photon will not go from 0 to 200 but breaks at a certain groove number - lets say at number 15. In the geometry viewer, i can now again see all grooves, but only the "inner part" of the lens - the first 15 grooves gives the expected behavior for the photos, all other grooves (16-200) are not present for the photons.

I attached 2 pictures of the geometry viewer zooming into the lens and showing one groove. The real Profile is marked in red. The groove profile with the falling edge does not lead to any problem, but the second picture showing a groove profile with a positive pitch at the end, so that the grooves touch each other with a face will lead to the described problem.

The fact, that this minimal change in geometry causes the problem makes me think that it could be a bug, but i am very new to Geant4 and to C++ so i dont have a clue.

Does anyone have an idea about that ? Thank you very much !

Best regards, Michael Eichler

   Attachment:
      http://hypernews.slac.stanford.edu/HyperNews/geant4/get/AUX/2013/07/23/09.29-57705-groove_working.png
      http://hypernews.slac.stanford.edu/HyperNews/geant4/get/AUX/2013/07/23/09.29-93096-groove_notworking.png

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1 None: Re: problem with G4Polycone in fresnel lens   (John Apostolakis - 23 Jul, 2013)
(_ More: Re: problem with G4Polycone in fresnel lens   (Michael Eichler - 24 Jul, 2013)
(_ News: Re: problem with G4Polycone in fresnel lens   (Michael Eichler - 31 Jul, 2013)
(_ None: Re: problem with G4Polycone in fresnel lens   (Tatiana Nikitina - 31 Jul, 2013)
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