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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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