| [807] | 1 | -------------------------------------------------------------------
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| 2 |
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| 3 | =========================================================
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| 4 | Geant4 - an Object-Oriented Toolkit for Simulation in HEP
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| 5 | =========================================================
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| 6 |
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| 7 | purgin_magnet
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| 8 | -------------
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| 9 | s. Larsson, May 2004
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| 10 |
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| 11 | -----------------------------------------------------------------
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| 12 | Acknowledgments to GEANT4 people, in particular to J. Apostolakis,
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| 13 | J Generowicz, G. Folger, Vladimir Ivanchenko, M.G.Pia and
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| 14 | S. Guatelli.
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| 15 | -----------------------------------------------------------------
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| 16 |
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| 17 | 0. Introduction
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| 18 | ----------------
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| 19 |
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| 20 | This example simulates electrons traveling through a 3D magnetic field.
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| 21 |
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| 22 | The Purging Magnet example is an application of Geant4 in a medical
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| 23 | environment. It simulates a strong purging magnet in a treatment head.
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| 24 | The geometry is very simplified. The major idea of this example is to
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| 25 | implement an external magnetic field grid and test if the deviation of
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| 26 | electrons are as expected in this particular field. The data (position,
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| 27 | energy and momentum) are collected in a measurement volume.The data is
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| 28 | stored in a HBOOK file if the user has set up the AIDA 3.0 environment
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| 29 | and Anaphe is available.
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| 30 |
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| 31 |
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| 32 | 1. Setting up the environment variables
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| 33 | ---------------------------------------
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| 34 | -example enviroment with the compiler 3.2.3
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| 35 | -a standard Geant4 example GNUmakefile is provided
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| 36 |
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| 37 | setup with:
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| 38 | compiler = gcc-3.2.3
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| 39 | G4SYSTEM = linux-g++
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| 40 |
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| 41 | The following environment variables need to be set:
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| 42 |
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| 43 | G4LEDATA: points to low energy data base - G4EMLOW2.3
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| 44 |
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| 45 | setup for analysis: AIDA 3.2.1, PI 1.2.1
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| 46 |
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| 47 | Users can download the analysis tools from:
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| 48 |
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| 49 | http://aida.freehep.org/
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| 50 | http://www.cern.ch/PI
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| 51 |
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| 52 | The required data-file for the field map can be downloaded from:
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| 53 | http://cern.ch/geant4/source/source/PurgMag3D.TABLE.gz
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| 54 |
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| 55 |
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| 56 | 2. How to run the example
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| 57 | -------------------------
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| 58 |
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| 59 | - Run the "PurgMag" executable.
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| 60 | - File PurgMag.TABLE needs to be available in the current directory in order to run correctly.
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| 61 | - For visualisation use vis.mac.
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| 62 | Default visualization is with OpenGL
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| 63 | - Interactive or batch modes possible.
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| 64 | Default: Interactive mode.
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| 65 |
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| 66 | To run a certain number of events in interactive mode,
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| 67 | type the following at the "idle>" prompt:
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| 68 |
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| 69 | idle> run/beamOn NumberOfEvents
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| 70 | idle> exit
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| 71 |
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| 72 | - Simulation histogram output is stored in purgmag.hbk
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| 73 |
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| 74 | 1)Ntuple with position, energy and momentum for electrons
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| 75 | 2)Ntuple with position, energy and momentum for photons
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| 76 | (not needed in this example, will be used in further development)
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| 77 | 3)Ntuple with position, energy and momentum for positrons
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| 78 | (not needed in this example, will be used in further development)
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| 79 |
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| 80 | A default vizualisation macro (vis.mac) is pre-loaded before interactive runs.
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| 81 | Executing it
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| 82 | osmachine.3% $G4WORKDIR/bin/Linux-g++/PurgMag
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| 83 | runs vis.mac before giving you an interactive prompt.
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| 84 |
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| 85 |
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| 86 | 3. Detector description
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| 87 | -----------------------
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| 88 |
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| 89 | Simply a measurement volume. All particles entering the volume are scored.
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| 90 |
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| 91 |
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| 92 | 4. Physics processes
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| 93 | --------------------
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| 94 |
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| 95 | This example uses the standard Electromagnetic processes.
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| 96 |
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| 97 |
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| 98 | 5. Particle Generator
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| 99 | ----------------------
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| 100 |
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| 101 | The PurgMagPrimaryGeneratorAction sets the initial state of tracks to
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| 102 |
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| 103 | -electrons 50MeV
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| 104 | -Start position (0, 0, 15cm)
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| 105 | -Momentum direction (0, 0, -1)
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| 106 |
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| 107 |
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| 108 | 6. Geometry and materials
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| 109 | --------------------------
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| 110 |
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| 111 | The world consists of Vacuum to minimize interactions of the electrons
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| 112 | with the medium. The purging magnet is implemented as a 3D field grid
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| 113 | of field values and geometerically as a pole gap made of iron. The
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| 114 | measurement volume also contains vacuum.
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| 115 |
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| 116 | The field is interpolated using a simple linear interpolation in two
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| 117 | dimensions (z and rho).
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| 118 |
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| 119 | 7. Comparison
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| 120 | --------------
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| 121 |
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| 122 | The design of the magnetic field was made with the OPERA 3D package
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| 123 | which is an electromagnetic finite element and finite difference
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| 124 | analysis software. The deviation in the y-direction (ey in Ntuple 1)
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| 125 | has also been calculated in the OPERA 3D module TOSCA for comparison.
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| 126 |
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| 127 | TOSCA: deviation y-direction: 35.112 cm
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| 128 | GEANT4: deviation y-direction: 35.170 cm (updated after PurgMag.pdf)
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| 129 |
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| 130 | ****************************************************************
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| 131 | * *
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| 132 | * More information about the setup and geometry in PurgMag.pdf *
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| 133 | * *
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| 134 | ****************************************************************
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