Gabriele Cosmo
128 lines
5.0 KiB
Plaintext
128 lines
5.0 KiB
Plaintext
$Id: README 100688 2016-10-31 11:21:51Z gcosmo $
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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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field01
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-------
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Example enabling investigation of tracking in a magnetic field.
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The key capabilities of this example are creating a uniform magnetic
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field interactively using the field messenger.
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The capabilities are demonstrated in the field.in file:
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/field/setStepperType 4
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/field/setMinStep 0.1 mm
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/field/update
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There are several potential choices of the stepper type. Here are some suggestions:
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===========================================================================
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Number Name of Stepper Comments
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===========================================================================
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Recommended - new in Geant4 10.3-beta:
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15 - Dormand Prince 745 : well-known and very efficient embedded method
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Highly recommended in literature, including
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Hairer & Wanner, & even Numerical Recipes
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Used in several established RK code (e.g. DOPRI5)
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===========================================================================
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Good choices for reasonably smooth fields:
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8 - Cash Karp RKF 45 : Old 'embedded' RK method - fairly robust,
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Uses a pair 4th & 5th order formulae;
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the difference is the error estimate.
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Faster than old 'simple' that use two half
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steps to estimate error.
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Available since Geant4 1.0
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45 - BogackiShampine45 : More efficient embedded 4/5 pair
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Used in many applications, including
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RKSUITE suite.
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New in Geant4 10.3-beta:
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===========================================================================
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Default - good choice for unknown fields:
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4 - ClassicalRK4 : original Runge-Kutta method, very robust but slower )
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( obtains error estimate by doing 2 half steps )
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===========================================================================
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Good choices for non-smooth fields (with kinks, abrupt changes):
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3 - SimpleHeum : low order, with error obtained from half-steps
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23 - BogackiShampine23 : lower order embedded method (new in 10.3-beta)
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===========================================================================
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Background Information
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1- GEOMETRY DEFINITION
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The "absorber" is a solid made of a given material.
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Three parameters define the absorber :
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- the material of the absorber,
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- the thickness of an absorber,
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- the transverse size of the absorber (the input face is a square).
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The volume "World" contains the "absorber".
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In this test the parameters of the "World" can be changed , too.
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In addition a transverse uniform magnetic field can be applied.
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The default geometry is constructed in F01DetectorConstruction class,
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but all the parameters can be changed via
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the commands defined in the F01DetectorMessenger class.
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2- AN EVENT : THE PRIMARY GENERATOR
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The primary kinematic consists of a single particle (proton, Ekin = 1 GeV)
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which hits the
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absorber perpendicular to the input face. The type of the particle
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and its energy are set in the F01PrimaryGeneratorAction class, and can
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be changed via the G4 build-in commands of G4ParticleGun class (see
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the macros provided with this example).
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A RUN is a set of events.
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3- DETECTOR RESPONSE
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The spatial distribution of charged particles transported in magnetic
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field is envistigated.
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A HIT is a record, event per event , of all the
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informations needed to simulate and analyse the detector response.
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In this example a F01CalorHit is defined as a set of 2 informations:
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- the total energy deposit in the absorber,
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- the total tracklength of all charged particles in the absorber,
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Therefore the absorber is declared
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'sensitive detector' (SD), see F01CalorimeterSD, which means they can contribute to the hit.
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4- PHYSICS LIST
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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 the FTFP_BERT physics list. This physics list
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requires data files for electromagnetic and hadronic processes.
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See more on installation of the datasets in Geant4 Installation Guide,
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5- HOW TO START ?
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- execute field01 in 'batch' mode from macro file e.g.
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% field01 field01.in
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- execute field01 in 'interactive' mode with visualization e.g.
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% field01
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....
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Idle> /control/execute vis.mac
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....
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