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1 -------------------------------------------------------------------
2
3 =========================================================
4 Geant4 - an Object-Oriented Toolkit for Simulation in HEP
5 =========================================================
6
7 purgin_magnet
8 -------------
9 s. Larsson, May 2004
10
11 -----------------------------------------------------------------
12 Acknowledgments to the GEANT4 Collaboration, in particular to J. Apostolakis,
13 J Generowicz, G. Folger, Vladimir Ivanchenko, M.G.Pia and
14 S. Guatelli.
15 -----------------------------------------------------------------
16
17 0. Introduction
18 ----------------
19
20 This example simulates electrons traveling through a 3D magnetic field.
21
22 The Purging Magnet example is an application of Geant4 in a medical
23 environment. It simulates a strong purging magnet in a treatment head.
24 The geometry is very simplified. The major idea of this example is to
25 implement an external magnetic field grid and test if the deviation of
26 electrons are as expected in this particular field. The data (position,
27 energy and momentum) are collected in a measurement volume. The data is
28 stored in a CSV file (or, optionally in a ROOT, or a XML file, by changing
29 the G4AnalysisManager default file type in PurgMagRunAction::Book().
30
31 <<<<<<< HEAD
32
33 =======
34 >>>>>>> Migration to G4RunManagerFactory done.
35 1. Setting up the environment variables
36 ---------------------------------------
37
38 The following environment variables need to be set:
39
40 G4LEDATA: points to low energy data base
41
42 The required data-file for the detailed field map can be downloaded from:
43 http://cern.ch/geant4-data/datasets/PurgMag3D.TABLE.gz
44
45
46 2. How to run the example
47 -------------------------
48
49 - Run the "PurgMag" executable.
50 - File PurgMag.TABLE needs to be available in the current directory in order to run correctly.
51 - For visualisation use vis.mac.
52 - Interactive or batch modes possible.
53 Default: Interactive mode.
54
55 To run a certain number of events in interactive mode,
56 type the following at the "idle>" prompt:
57
58 idle> run/beamOn NumberOfEvents
59 idle> exit
60
61 - Simulation histogram output is stored in purgmag_101.cvs (e-),
62 purgmag_102.cvs (gammas), purgman_103.cvs (e+)
63
64 1)Ntuple with position, energy and momentum for electrons
65 2)Ntuple with position, energy and momentum for photons
66 (not needed in this example, will be used in further development)
67 3)Ntuple with position, energy and momentum for positrons
68 (not needed in this example, will be used in further development)
69
70 A default visualisation macro (vis.mac) is pre-loaded before interactive runs.
71 Executing it from the build directory:
72 $ ./PurgMag
73 runs vis.mac before giving you an interactive prompt.
74
75
76 3. Detector description
77 -----------------------
78
79 Simply a measurement volume. All particles entering the volume are scored.
80
81
82 4. Physics processes
83 --------------------
84
85 This example uses the standard Electromagnetic processes.
86
87
88 5. Particle Generator
89 ----------------------
90
91 The PurgMagPrimaryGeneratorAction sets the initial state of tracks to
92
93 -electrons 50MeV
94 -Start position (0, 0, 15cm)
95 -Momentum direction (0, 0, -1)
96
97
98 6. Geometry and materials
99 --------------------------
100
101 The world consists of Vacuum to minimize interactions of the electrons
102 with the medium. The purging magnet is implemented as a 3D field grid
103 of field values and geometerically as a pole gap made of iron. The
104 measurement volume also contains vacuum.
105
106 The field is interpolated using a simple linear interpolation in two
107 dimensions (z and rho).
108
109 7. Comparison
110 --------------
111
112 The design of the magnetic field was made with the OPERA 3D package
113 which is an electromagnetic finite element and finite difference
114 analysis software. The deviation in the y-direction (ey in Ntuple 1)
115 has also been calculated in the OPERA 3D module TOSCA for comparison.
116
117 TOSCA: deviation y-direction: 35.112 cm
118 GEANT4: deviation y-direction: 35.170 cm (updated after PurgMag.pdf)
119
120 ****************************************************************
121 * *
122 * More information about the setup and geometry in PurgMag.pdf *
123 * *
124 ****************************************************************
