Gabriele Cosmo
192 lines
7.0 KiB
Plaintext
192 lines
7.0 KiB
Plaintext
$Id: README,v 1.16 2005/11/22 16:11:04 maire Exp $
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-------------------------------------------------------------------
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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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ExampleN03
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----------
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This example simulates a simple Sampling Calorimeter setup.
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1- GEOMETRY DEFINITION
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The calorimeter is a box made of a given number of layers. A layer
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consists of an absorber plate and of a detection gap. The layer is
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replicated.
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Six parameters define the calorimeter :
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- the material of the absorber,
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- the thickness of an absorber plate,
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- the material of the detection gap,
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- the thickness of a gap,
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- the number of layers,
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- the transverse size of the calorimeter (the input face is a square).
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In addition a transverse uniform magnetic field can be applied.
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The default geometry is constructed in DetectorConstruction class,
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but all of the above parameters can be modified interactively via
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the commands defined in the DetectorMessenger class.
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|<----layer 0---------->|<----layer 1---------->|<----layer 2---------->|
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==========================================================================
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|| absorber | gap || absorber | gap || absorber | gap ||
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beam || | || | || | ||
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======> || | || | || | ||
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==========================================================================
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NB. The thickness of the absorber or of the gap can be set to zero
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(but not together), and the number of layers to 1. In this case we
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have a unique homogeneous block of matter, which looks like
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a bubble chamber rather than a calorimeter ...
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(see the macro of commands: newgeom.mac)
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2- AN EVENT : THE PRIMARY GENERATOR
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The primary kinematic consists of a single particle which hits the
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calorimeter perpendicular to the input face. The type of the particle
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and its energy are set in the PrimaryGeneratorAction class, and can
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be changed via the G4 build-in commands of ParticleGun class (see
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the macros provided with this example).
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In addition one can choose randomly the impact point of the incident
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particle. The corresponding interactive command is built in
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PrimaryGeneratorMessenger class (see run2.mac).
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A RUN is a set of events.
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3- VISUALIZATION
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The Visualization Manager is set in the main().
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The initialisation of the drawing is done via a set of /vis/ commands
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in the macro vis.mac. This macro is automatically read from
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the main in case of interactive running mode.
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By default, vis.mac opens a DAWNFILE, suitable for viewing in DAWN,
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and an OGLX for OpenGl.
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You can switch to other graphics systems by commenting out this line
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and instead uncommenting one of the other /vis/open statements, such as
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HepRepFile or HepRepXML.
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The DAWNFILE, HepRepFile and HepRepXML drivers are always available
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(since they require no external libraries), but the OGLIX driver
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requires:
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1- the visualisation & interfaces categories have been compiled
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with the environment variable G4VIS_BUILD_OPENGLX_DRIVER.
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2- exampleN03.cc has been compiled with G4VIS_USE_OPENGLX.
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The HepRepXML driver outputs a zip file that can be unzipped into
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several individual HepRep files, each viewable in WIRED.
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For more information on visualization, including information on how to
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install and run DAWN, OpenGL and WIRED, see the visualization tutorials
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on the Geant4 Workshop Tutorial CD available at:
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http://geant4.slac.stanford.edu/g4cd/Welcome.html
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The detector has a default view which is a longitudinal view of the
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calorimeter.
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The tracks are drawn at the end of event, and erased at the end of run.
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Optionaly one can choose to draw all particles, only the charged,
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or neutral or none. This command is build in EventActionMessenger class.
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Additional visualization tutorial macros are available in the visTutor
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subdirectory. They can be tried as:
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% $G4BINDIR/exampleN03
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idle > /control/execute visTutor/exN03VisX.mac
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For details, see comment lines described in the macro files.
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These macros are designed to help your understanding the User's Guide.
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4- PHYSICS DEMO
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The particle's type and the physic processes which will be available
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in this example are set in PhysicsList class.
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In addition the build-in interactive command:
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/process/(in)activate processName
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allows to activate/inactivate the processes one by one.
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Then one can well visualize the processes one by one, especially
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in the bubble chamber setup with a transverse magnetic field.
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(see run2.mac and newgeom.mac)
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As a homework try to visualize a gamma conversion alone,
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or the effect of the multiple scattering.
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5- RANDOM NUMBERS HANDLING
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CLHEP provides several random number engines. In this example the Ranecu
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engine is choosen at beginning of the main (exampleN03.cc).
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By default, G4RunManager does not save the rndm seed.
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To do so the user must set in BeginOfRunAction:
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G4RunManager::GetRunManager()->SetRandomNumberStore(true);
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Then the rndm seed is systematically saved at beginning of run
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(currentRun.rndm) and beginning of event (currentEvent.rndm)
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Therefore, in case of abnormal end, the seed of the last event processed
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is available in currentEvent.rndm
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Even in case of normal run processing, the user may wish to preserve the
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rndm seed of selected events. At any time in the event, put the
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following statement:
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if (condition) G4RunManager::GetRunManager()->rndmSaveThisEvent();
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currentEvent.rndm will be copied to runXXevntYY.rndm
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(see ExN03SteppingAction::UserSteppingAction() )
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To restart a run from a given rndm seed, use the UI command :
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/random/resetEngineFrom fileName
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The macro rndmSeed.mac shows how to save and reset the random number
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seed between runs, from UI commands.
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6- USER INTERFACES
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The default command interface, called G4UIterminal, is done via
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standart cin/G4cout.
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On Linux and Sun-cc on can use a smarter command interface G4UItcsh.
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It is enough to set the environment variable G4UI_USE_TCSH
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On can use a Motif driven command interface (called G4UIXm) if:
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1- interfaces category has been compiled with G4UI_BUILD_XM_SESSION
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2- exampleN03.cc has been compiled with G4UI_USE_XM.
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7- HOW TO START ?
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- compile and link to generate an executable
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% cd N03
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% gmake
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- execute N03 in 'batch' mode from macro files
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% exampleN03 run1.mac
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- execute N03 in 'interactive mode' with visualization
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% exampleN03
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....
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Idle> ---> type your commands. For instance:
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Idle> /run/beamOn
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....
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Idle> /run/beamOn 10
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....
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Idle> /control/execute newgeom.mac
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....
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Idle> exit
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