Gabriele Cosmo
96 lines
3.0 KiB
Plaintext
96 lines
3.0 KiB
Plaintext
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Geant4 - an Object-Oriented Toolkit for Simulation in HEP
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WLS
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This application simulates the propagation of optical photons inside a
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Wave Length Shifting (WLS) fiber.
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1- Geometry Definition
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The default geometry is as follow:
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- A perfect, bare (or clad), PMMA fiber: 0.5mm radius, 2m length at
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center (0,0,0) of the World.
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- A circular MPPC with 0.5mm radius at the +z end of the fiber
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- World and coupling materials are G4_AIR
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- Photons will always refracted out to coupling material before
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reaching MPPC
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- There are many flexible parameters that the user could specify.
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They are under the /WLS directory of help.
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2- Material Choices
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There are several materials that the user can use for the fiber core,
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world and coupling.
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They are:
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- Vacuum (G4_Galactic)
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- Air (G4_AIR)
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- PMMA, refractive index n = 1.60
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- Pethylene, n = 1.49
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- FPethylene, n = 1.42
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- Polystyrene, n = 1.60
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- Silicone, n = 1.46
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3- Photon Source
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This program uses the General Particle Source (G4GeneralParticleSource)
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provided by Geant4 for generating particles. The energy of a primary
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optical photon must be within the range 2.00 eV to 3.47 eV.
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4- Hit
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A hit is registered when an optical photon is absorbed on the MPPC
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surface. Information stored in a hit includes the local coordinate of the
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location the optical photon is absorbed on the MPPC, the global coordinate
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where the optical photon left the fiber, the transit time of the optical
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photon, and the energy of the optical photon.
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5- Stepping Action
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The stepping action keeps track of the number of bounces an optical photon has
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gone through. In order to prevent infinite loop and extremely skewed
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rays taking up computing time, there is a limit of the number of
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bounces that an optical photon can go through before it is artificially killed.
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The default limit is 100,000. The user can set his/her own limit using
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the /stepping/setBounceLimit command. A value of 0 will turn off the
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limit. All optical photons artificially killed will have murderee flag turned
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on in their UserTrackInformation.
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6- Visualization
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To visualize particle trajectories, simply use vis.mac macro in
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interactive mode or in your own macro.
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7- main()
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- execute wls in 'batch' mode from macro files
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- you can enter an optional integer seed for batch mode
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% wls electron.mac (optional: enter an integer seed here)
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- wls in 'interactive mode' with visualization
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% wls
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....
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Idle> /control/execute
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Idle> /run/beamOn 1
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....
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Idle> exit
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8- Macros provided
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- electron.mac: Sets up the geometry and configures the particle source.
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Primary particle is a 10 MeV electron.
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- vis.mac: macro for visualization; called automatically when no macro is
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given on command line.
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