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0001 =========================================================
0002 Geant4 - an Object-Oriented Toolkit for Simulation in HEP
0003 =========================================================
0004
0005 WLS
0006 ----------
0007
0008 This application simulates the propagation of optical photons inside a
0009 Wave Length Shifting (WLS) fiber.
0010
0011
0012 1- Geometry Definition
0013
0014 The default geometry is as follow:
0015
0016 - A perfect, bare (or clad), PMMA fiber: 0.5mm radius, 2m length at
0017 center (0,0,0) of the World.
0018 - A circular MPPC with 0.5mm radius at the +z end of the fiber
0019 - World and coupling materials are G4_AIR
0020 - Photons will always refracted out to coupling material before
0021 reaching MPPC
0022 - There are many flexible parameters that the user could specify.
0023 They are under the /WLS directory of help.
0024
0025
0026 2- Material Choices
0027
0028 There are several materials that the user can use for the fiber core,
0029 world and coupling.
0030
0031 They are:
0032
0033 - Vacuum (G4_Galactic)
0034 - Air (G4_AIR)
0035 - PMMA, refractive index n = 1.60
0036 - Pethylene, n = 1.49
0037 - FPethylene, n = 1.42
0038 - Polystyrene, n = 1.60
0039 - Silicone, n = 1.46
0040
0041
0042 3- Photon Source
0043
0044 This program uses the General Particle Source (G4GeneralParticleSource)
0045 provided by Geant4 for generating particles. The energy of a primary
0046 optical photon must be within the range 2.00 eV to 3.47 eV.
0047
0048
0049 4- Hit
0050
0051 A hit is registered when an optical photon is absorbed on the MPPC
0052 surface. Information stored in a hit includes the local coordinate of the
0053 location the optical photon is absorbed on the MPPC, the global coordinate
0054 where the optical photon left the fiber, the transit time of the optical
0055 photon, and the energy of the optical photon.
0056
0057
0058 5- Stepping Action
0059
0060 The stepping action keeps track of the number of bounces an optical photon has
0061 gone through. In order to prevent infinite loop and extremely skewed
0062 rays taking up computing time, there is a limit of the number of
0063 bounces that an optical photon can go through before it is artificially killed.
0064 The default limit is 100,000. The user can set his/her own limit using
0065 the /stepping/setBounceLimit command. A value of 0 will turn off the
0066 limit. All optical photons artificially killed will have murderee flag turned
0067 on in their UserTrackInformation.
0068
0069
0070 6- Visualization
0071
0072 To visualize particle trajectories, simply use vis.mac macro in
0073 interactive mode or in your own macro.
0074
0075
0076 7- main()
0077
0078 - execute wls in 'batch' mode from macro files
0079 - you can enter an optional integer seed for batch mode
0080 % wls electron.mac (optional: enter an integer seed here)
0081
0082 - wls in 'interactive mode' with visualization
0083 % wls
0084 ....
0085 Idle> /control/execute
0086 Idle> /run/beamOn 1
0087 ....
0088 Idle> exit
0089
0090 8- Macros provided
0091
0092 - electron.mac: Sets up the geometry and configures the particle source.
0093 Primary particle is a 10 MeV electron.
0094 - vis.mac: macro for visualization; called automatically when no macro is
0095 given on command line.
