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Question Cherenkov photons and reflections  

Forum: Processes Involving Optical Photons
Date: 14 May, 2013
From: <bg92>

Hello,

I am trying to implement a Cherenkov detector using QUARTZ material. The idea here is to make a plane of 34 QUARTZ bars (17.25mm, 35mm, 4.9m) perpendicular to the beam axis. You can see an overview with the Figure 1 attached. The bars are located inside a (yellow) box filled with C4F10 gaz (the Cherenkov photons produced with this gas are reflected by mirrors which are not displayed here). The red track is a Pion.

The index of refraction of the QUARTZ is really high: 1.473, so that the number of photons produced is huge (approx 440/cm) with a Cherenkov angle of about 47 with respect to the incoming particle.

The idea of this design is to trap the Cherenkov photons inside the QUARTZ bars, (just like in a fiber optics) and to transport the signal to each ends of the bar.

My problem here is that I can't run this simulation with n=1.473. To produce the plots attached, I had to set n=1.2 . Doing so, the simulation for one single event (one thrown pion), takes about 13 seconds to run... If I set n=1.473, the simulation never ends.

I think the problem is coming from the fact that for n=1.2, only a small part of the photons are reflected and trapped inside the QUARTZ bar, while for n=1.473, almost all the photons are trapped and transported to the ends of the bars. That means a large amount of reflections and computations.

I tried to play with differents parameters in order to minimize the number of photons produced: theCerenkovProcess->SetMaxNumPhotonsPerStep(1); theCerenkovProcess->SetMaxBetaChangePerStep(0.1); theCerenkovProcess->SetTrackSecondariesFirst(true); but that does not change the problem.

So do you know how I can run this simulation more rapidly, and with n=1.473 ??

Thanks you very much for your help.

Regards, Baptiste

   Attachment:
      http://hypernews.slac.stanford.edu/HyperNews/geant4/get/AUX/2013/05/14/11.52-44044-Pic1.jpg
      http://hypernews.slac.stanford.edu/HyperNews/geant4/get/AUX/2013/05/14/11.52-70745-Pic2.jpg
      http://hypernews.slac.stanford.edu/HyperNews/geant4/get/AUX/2013/05/14/11.52-49157-Pic3.jpg

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1 Feedback: Re: Cherenkov photons and reflections   (Gumplinger Peter - 14 May, 2013)
(_ Question: Re: Cherenkov photons and reflections   (bg92 - 16 May, 2013)
(_ Feedback: Re: Cherenkov photons and reflections   (Gumplinger Peter - 16 May, 2013)
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