Gabriele Cosmo
135 lines
4.7 KiB
Plaintext
135 lines
4.7 KiB
Plaintext
-------------------------------------------------------------------
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=========================================================
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Geant4 - an Object-Oriented Toolkit for Simulation in HEP
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=========================================================
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purgin_magnet
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-------------
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s. Larsson, May 2004
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Acknowledgments to GEANT4 people, in particular to J. Apostolakis,
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J Generowicz, G. Folger, Vladimir Ivanchenko, M.G.Pia and
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S. Guatelli.
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0. Introduction
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----------------
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This example simulates electrons traveling through a 3D magnetic field.
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The Purging Magnet example is an application of Geant4 in a medical
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environment. It simulates a strong purging magnet in a treatment head.
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The geometry is very simplified. The major idea of this example is to
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implement an external magnetic field grid and test if the deviation of
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electrons are as expected in this particular field. The data (position,
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energy and momentum) are collected in a measurement volume.The data is
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stored in a HBOOK file if the user has set up the AIDA 3.0 environment
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and Anaphe is available.
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1. Setting up the environment variables
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---------------------------------------
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-example enviroment with the compiler 3.2.3
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-a standard Geant4 example GNUmakefile is provided
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setup with:
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compiler = gcc-3.2.3
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G4SYSTEM = linux-g++
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The following environment variables need to be set:
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G4LEDATA: points to low energy data base - G4EMLOW2.3
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setup for analysis: AIDA 3.2.1, PI 1.2.1
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Users can download the analysis tools from:
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http://aida.freehep.org/
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http://www.cern.ch/PI
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The required data-file for the field map can be downloaded from:
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http://cern.ch/geant4/source/source/PurgMag3D.TABLE.gz
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2. How to run the example
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-------------------------
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- Run the "PurgMag" executable.
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- File PurgMag.TABLE needs to be available in the current directory in order to run correctly.
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- For visualisation use vis.mac.
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Default visualization is with OpenGL
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- Interactive or batch modes possible.
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Default: Interactive mode.
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To run a certain number of events in interactive mode,
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type the following at the "idle>" prompt:
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idle> run/beamOn NumberOfEvents
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idle> exit
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- Simulation histogram output is stored in purgmag.hbk
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1)Ntuple with position, energy and momentum for electrons
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2)Ntuple with position, energy and momentum for photons
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(not needed in this example, will be used in further development)
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3)Ntuple with position, energy and momentum for positrons
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(not needed in this example, will be used in further development)
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A default vizualisation macro (vis.mac) is pre-loaded before interactive runs.
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Executing it
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osmachine.3% $G4WORKDIR/bin/Linux-g++/PurgMag
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runs vis.mac before giving you an interactive prompt.
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3. Detector description
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-----------------------
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Simply a measurement volume. All particles entering the volume are scored.
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4. Physics processes
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--------------------
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This example uses the standard Electromagnetic processes.
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5. Particle Generator
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----------------------
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The PurgMagPrimaryGeneratorAction sets the initial state of tracks to
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-electrons 50MeV
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-Start position (0, 0, 15cm)
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-Momentum direction (0, 0, -1)
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6. Geometry and materials
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--------------------------
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The world consists of Vacuum to minimize interactions of the electrons
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with the medium. The purging magnet is implemented as a 3D field grid
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of field values and geometerically as a pole gap made of iron. The
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measurement volume also contains vacuum.
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The field is interpolated using a simple linear interpolation in two
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dimensions (z and rho).
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7. Comparison
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--------------
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The design of the magnetic field was made with the OPERA 3D package
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which is an electromagnetic finite element and finite difference
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analysis software. The deviation in the y-direction (ey in Ntuple 1)
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has also been calculated in the OPERA 3D module TOSCA for comparison.
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TOSCA: deviation y-direction: 35.112 cm
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GEANT4: deviation y-direction: 35.170 cm (updated after PurgMag.pdf)
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****************************************************************
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* *
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* More information about the setup and geometry in PurgMag.pdf *
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* *
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****************************************************************
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