| Geant4 Cross Reference |
1 ========================================================= 2 Geant4 - an Object-Oriented Toolkit for Simulation in HEP 3 ========================================================= 4 5 WLS 6 ---------- 7 8 This application simulates the propagation of optical photons inside a 9 Wave Length Shifting (WLS) fiber. 10 11 12 1- Geometry Definition 13 14 The default geometry is as follow: 15 16 - A perfect, bare (or clad), PMMA fiber: 0.5mm radius, 2m length at 17 center (0,0,0) of the World. 18 - A circular MPPC with 0.5mm radius at the +z end of the fiber 19 - World and coupling materials are G4_AIR 20 - Photons will always refracted out to coupling material before 21 reaching MPPC 22 - There are many flexible parameters that the user could specify. 23 They are under the /WLS directory of help. 24 25 26 2- Material Choices 27 28 There are several materials that the user can use for the fiber core, 29 world and coupling. 30 31 They are: 32 33 - Vacuum (G4_Galactic) 34 - Air (G4_AIR) 35 - PMMA, refractive index n = 1.60 36 - Pethylene, n = 1.49 37 - FPethylene, n = 1.42 38 - Polystyrene, n = 1.60 39 - Silicone, n = 1.46 40 41 42 3- Photon Source 43 44 This program uses the General Particle Source (G4GeneralParticleSource) 45 provided by Geant4 for generating particles. The energy of a primary 46 optical photon must be within the range 2.00 eV to 3.47 eV. 47 48 49 4- Hit 50 51 A hit is registered when an optical photon is absorbed on the MPPC 52 surface. Information stored in a hit includes the local coordinate of the 53 location the optical photon is absorbed on the MPPC, the global coordinate 54 where the optical photon left the fiber, the transit time of the optical 55 photon, and the energy of the optical photon. 56 57 58 5- Stepping Action 59 60 The stepping action keeps track of the number of bounces an optical photon has 61 gone through. In order to prevent infinite loop and extremely skewed 62 rays taking up computing time, there is a limit of the number of 63 bounces that an optical photon can go through before it is artificially killed. 64 The default limit is 100,000. The user can set his/her own limit using 65 the /stepping/setBounceLimit command. A value of 0 will turn off the 66 limit. All optical photons artificially killed will have murderee flag turned 67 on in their UserTrackInformation. 68 69 70 6- Visualization 71 72 To visualize particle trajectories, simply use vis.mac macro in 73 interactive mode or in your own macro. 74 75 76 7- main() 77 78 - execute wls in 'batch' mode from macro files 79 - you can enter an optional integer seed for batch mode 80 % wls electron.mac (optional: enter an integer seed here) 81 82 - wls in 'interactive mode' with visualization 83 % wls 84 .... 85 Idle> /control/execute 86 Idle> /run/beamOn 1 87 .... 88 Idle> exit 89 90 8- Macros provided 91 92 - electron.mac: Sets up the geometry and configures the particle source. 93 Primary particle is a 10 MeV electron. 94 - vis.mac: macro for visualization; called automatically when no macro is 95 given on command line.