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examples/extended/field/.README.txt
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///\file "field/.README.txt"
///\brief Examples field README page
/*! \page Examples_field Category "field"
Examples in this directory demonstrate specific simulation setups
in magnetic field.
\link Examplefield01 field01 \endlink
Example enabling investigation of tracking in a magnetic field.
\link Examplefield02 field02 \endlink
Test for investigation of tracking in electric field and field dependent
electromagnetic processes.
\link Examplefield03 field03 \endlink
Example of tracking in magnetic field where field associated
to selected logical volumes varies.
\link Examplefield04 field04 \endlink
This example shows how to define/use OVERLAPPING field elements
in Geant4. Fields might be either magnetic, electric or both.
\link Examplefield05 field05 \endlink
This example demonstrates so-called "spin-frozen" condition.
\link Examplefield06 field06 \endlink
This example exercises the capability of tracking massive
particles in a gravity field.
\link ExampleBlineTracer BlineTracer \endlink
The BlineTracer module allows to trace and visualise magnetic field
lines in a Geant4 application where particle are tracked through the
magnetic field (in future, these functionalities may be integrated in
the Geant4 kernel).
*/
examples/extended/field/BlineTracer/.README.txt
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///\file "field/BlineTracer/.README.txt"
///\brief Example BlineTracer README page
/*! \page ExampleBlineTracer Example BlineTracer
\author Laurent Desorgher (desorgher@phim.unibe.ch) - 04/10/2003
The BlineTracer module allows to trace and visualise magnetic field
lines in a Geant4 application where particle are tracked through the
magnetic field (in future, these functionalities may be integrated in
the Geant4 kernel).
To use the tracer, the user should copy the classes provided here in
his/her own application/example and create somewhere in his/her code
an instance of a G4BlineTracer object.
It can be anywhere (for example in the main code or in the user class
defining the magnetic field):
\verbatim
#include "G4BlineTracer.hh"
G4BlineTracer* theBlineTool = new G4BlineTracer();
\endverbatim
\section ExampleBlineTracer_s1 Design principles
The core of the tool is the method G4BlineTracer::ComputeBlines() of G4BlineTracer class.
In this method a bline is computed by tracking a ChargedGeantino in the user
defined magnetic field and by using a Bline equation of motion (class
G4BlineEquation, motion along the field) instead of a Lorentz equation.
During the execution of this method :
- The user defined equations of motion associated to the different
global and local fields are replaced by instances of G4BlineEquation
associated to the same fields.
The G4BlineEquation class defines the differential equation of a
magnetic field line.
- User defined ChordFinders are replaced by new ChordFinders
associated to the G4BlineEquation object.
- The user primary generator action, run action, event action and
stepping action are replaced by instances of the classes
G4BlinePrimaryGeneratorAction, G4BlineTracer, G4BlineEventAction
and G4BlineSteppingAction respectively. Other actions are set to
a NULL pointer.
After the execution of the method, the original user defined actions, equation
of motions and chord-finders are restored.
In other words, the deafult run-action is temporarly replaced by a
G4BlineTracer run-action using the same Geometry, physics and magnetic fields
but with a different equation of motion and user actions.
The G4BlinePrimaryGeneratorAction::GeneratePrimaries() method of the G4BlinePrimaryGeneratorAction class
call the GeneratePrimaries() method of the user defined PrimaryGeneratorAction
for defining the start position and start time of tracking.
Start position for user application and for Bline tracking are therefore
controlled by the same UI commands.
The type of particles to be tracked when tracing Blines is always set
to Charged-Geantino. This allows to switch off the effect of electromagnetic
and hadronics physics when tracing field lines.
The G4BlineEventAction class is responsible to store computed magnetic field
lines as a vector of Polylines and Polymarkers for later visualisation.
These vectors can be drawn and reset at any time.
The stepping action does nothing in this implementation but it can be used
in future versions to limit field line tracing to physical volumes defined
by the user. For this purpose a G4BlineStackingAction could also be
implemented.
\section ExampleBlineTracer_s2 User Manual
\subsection ExampleBlineTracer_subs21 General description
The BlineTracer is controlled by the UI commands contained in the directory
/vis/blineTracer. By calling the command 'computeBline', several magnetic field
lines passing through user defined start positions are computed.
Start positions are generated by the user primary generator action.
By doing so, the definition of start positions is the same for usual particles
tracking and magnetic field line tracking.
A magnetic field line is computed as a track of a charged geantino that moves
along the field line. The user can define the maximum length of a tracking step
(only valid for Bline tracing purposes) by the use of the 'setMaxStepLength'
command.
By using small enough maximum step length, smooth magnetic field lines are
obtained. By using the command 'stockLines' and 'stockPoints' the user
can decide to store the series of tracking step positions defining
a magnetic field line as a Polyline object and/or a PolyMarker object
(circles) respectively.
These objects are stored in vectors of PolyLines and PolyMarkers.
By using the command 'draw', these vectors are added to the scene
of the visualisation manager, provided that a scene handler and
visualisation driver have been properly created.
The scene is visualised by invoking the vis command '/vis/show'.
Polyline objects are visualised as line segments joining the different
step positions defining a line, while for a Polymarker object markers
(here circles), are drawn at each step positions.
By using the 'setColour' the user defines the visualisation colour
that will be associated to the next computed magnetic field lines.
By calling 'setPointSize' the user defines the size of visualisation markers
that will be associated to the next computed magnetic field lines.
The user can remove the vector of Polymarker and Polyline from the memory
by invoking 'resetMaterialToBeDrawn'.
When using small max step size and polymarkers for visualisation purposes, the
thickness of a smooth magnetic field line is obtained. It is controlled by the
Marker size parameter ('setPointSize')
\subsection ExampleBlineTracer_subs22 Command description
\verbatim
/vis/blineTracer/computeBline nb_of_lines
\endverbatim
- Parameters: integer nb_of_lines
- Description: Compute nb_of_lines different magnetic field lines
\verbatim
/vis/blineTracer/setMaxStepLength max_step_length
\endverbatim
- Parameters: double max_step_length
- Description: Set the maximum tracking step length for computing
magnetic field lines
\verbatim
/vis/blineTracer/setColour red green blue
\endverbatim
- Parameters: double red, green, blue
- Description: Define the colour for visualisation of the
next computed magnetic field lines. The color is
defined by a RGB code (red,green,blue) with all
parameters smaller than 1.
\verbatim
/vis/blineTracer/stockLines aBool
\endverbatim
- Parameters: boolean aBool
- Description: If true the next computed field lines are stored
as Polylines for further visualisation
\verbatim
/vis/blineTracer/stockLines aBool
\endverbatim
- Parameters: boolean aBool
- Description: If true the next computed field lines are stored
as Polymarkers for further visualisation
\verbatim
/vis/blineTracer/setPointSize point_size
\endverbatim
- Parameters: double point_size
- Description: set the size of the visualisation markers
that will be associated with the next computed
magnetic field lines
\verbatim
/vis/blineTracer/resetMaterialToBeDrawn
\endverbatim
- Parameters: none
- Description: The vector of Polyline and Polymarker representing
magnetic field lines to be visualised are removed
from memory
\verbatim
/tracking/storeTrajectory 1
\endverbatim
- If the storeTrajectory parameter is not set no field lines are
stored.
\section ExampleBlineTracer_s3 Current limitations & known problems
The tool is working properly only for detectors parts where magnetic
field are defined. It is planned in the future to stop the tracking of
field lines in regions where no fields are existing.
*/
examples/extended/field/BlineTracer/README
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README file for the Geant4 BlineTracer module
Author : Laurent Desorgher (desorgher@phim.unibe.ch) - 04/10/2003
-------------------------------------------------
The BlineTracer module allows to trace and visualise magnetic field
lines in a Geant4 application where particle are tracked through the
magnetic field (in future, these functionalities may be integrated in
the Geant4 kernel).
To use the tracer, the user should copy the classes provided here in
his/her own application/example and create somewhere in his/her code
an instance of a G4BlineTracer object.
It can be anywhere (for example in the main code or in the user class
defining the magnetic field):
#include "G4BlineTracer.hh"
G4BlineTracer* theBlineTool = new G4BlineTracer();
Design principles:
The core of the tool is the method ComputeBlines() of G4BlineTracer class.
In this method a bline is computed by tracking a ChargedGeantino in the user
defined magnetic field and by using a Bline equation of motion (class
G4BlineEquation, motion along the field) instead of a Lorentz equation.
During the execution of this method :
-The user defined equations of motion associated to the different
global and local fields are replaced by instances of G4BlineEquation
associated to the same fields.
The G4BlineEquation class defines the differential equation of a
magnetic field line.
-User defined ChordFinders are replaced by new ChordFinders
associated to the G4BlineEquation object.
-The user primary generator action, run action, event action and
stepping action are replaced by instances of the classes
G4BlinePrimaryGeneratorAction, G4BlineTracer, G4BlineEventAction
and G4BlineSteppingAction respectively. Other actions are set to
a NULL pointer.
After the execution of the method, the original user defined actions, equation
of motions and chord-finders are restored.
In other words, the deafult run-action is temporarly replaced by a
G4BlineTracer run-action using the same Geometry, physics and magnetic fields
but with a different equation of motion and user actions.
The GeneratePrimaries() method of the G4BlinePrimaryGeneratorAction class
call the GeneratePrimaries() method of the user defined PrimaryGeneratorAction
for defining the start position and start time of tracking.
Start position for user application and for Bline tracking are therefore
controlled by the same UI commands.
The type of particles to be tracked when tracing Blines is always set
to Charged-Geantino. This allows to switch off the effect of electromagnetic
and hadronics physics when tracing field lines.
The G4BlineEventAction class is responsible to store computed magnetic field
lines as a vector of Polylines and Polymarkers for later visualisation.
These vectors can be drawn and reset at any time.
The stepping action does nothing in this implementation but it can be used
in future versions to limit field line tracing to physical volumes defined
by the user. For this purpose a G4BlineStackingAction could also be
implemented.
User Manual:
General description:
The BlineTracer is controlled by the UI commands contained in the directory
/vis/blineTracer. By calling the command 'computeBline', several magnetic field
lines passing through user defined start positions are computed.
Start positions are generated by the user primary generator action.
By doing so, the definition of start positions is the same for usual particles
tracking and magnetic field line tracking.
A magnetic field line is computed as a track of a charged geantino that moves
along the field line. The user can define the maximum length of a tracking step
(only valid for Bline tracing purposes) by the use of the 'setMaxStepLength'
command.
By using small enough maximum step length, smooth magnetic field lines are
obtained. By using the command 'stockLines' and 'stockPoints' the user
can decide to store the series of tracking step positions defining
a magnetic field line as a Polyline object and/or a PolyMarker object
(circles) respectively.
These objects are stored in vectors of PolyLines and PolyMarkers.
By using the command 'draw', these vectors are added to the scene
of the visualisation manager, provided that a scene handler and
visualisation driver have been properly created.
The scene is visualised by invoking the vis command '/vis/show'.
Polyline objects are visualised as line segments joining the different
step positions defining a line, while for a Polymarker object markers
(here circles), are drawn at each step positions.
By using the 'setColour' the user defines the visualisation colour
that will be associated to the next computed magnetic field lines.
By calling 'setPointSize' the user defines the size of visualisation markers
that will be associated to the next computed magnetic field lines.
The user can remove the vector of Polymarker and Polyline from the memory
by invoking 'resetMaterialToBeDrawn'.
When using small max step size and polymarkers for visualisation purposes, the
thickness of a smooth magnetic field line is obtained. It is controlled by the
Marker size parameter ('setPointSize')
Command description:
/vis/blineTracer/computeBline nb_of_lines :
Parameters: integer nb_of_lines
Description: Compute nb_of_lines different magnetic field lines
/vis/blineTracer/setMaxStepLength max_step_length :
Parameters: double max_step_length
Description: Set the maximum tracking step length for computing
magnetic field lines
/vis/blineTracer/setColour red green blue
Parameters: double red, green, blue
Description: Define the colour for visualisation of the
next computed magnetic field lines. The color is
defined by a RGB code (red,green,blue) with all
parameters smaller than 1.
/vis/blineTracer/stockLines aBool
Parameters: boolean aBool
Description: If true the next computed field lines are stored
as Polylines for further visualisation
/vis/blineTracer/stockLines aBool
Parameters: boolean aBool
Description: If true the next computed field lines are stored
as Polymarkers for further visualisation
/vis/blineTracer/setPointSize point_size
Parameters: double point_size
DEscription: set the size of the visualisation markers
that will be associated with the next computed
magnetic field lines
/vis/blineTracer/resetMaterialToBeDrawn
Parameters: none
Description: The vector of Polyline and Polymarker representing
magnetic field lines to be visualised are removed
from memory
/tracking/storeTrajectory 1 :
If the storeTrajectory parameter is not set no field lines are
stored.
Current limitations & known problems:
The tool is working properly only for detectors parts where magnetic
field are defined. It is planned in the future to stop the tracking of
field lines in regions where no fields are existing.
examples/extended/field/README
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Geant4 extended examples - field
----------------------------------
Examples in this directory demonstrate specific simulation setups
in magnetic field.
field01
--------
Example enabling investigation of tracking in a magnetic field.
field02
--------
Test for investigation of tracking in electric field and field dependent
electromagnetic processes.
field03
--------
Example of tracking in magnetic field where field associated
to selected logical volumes varies.
field04
--------
This example shows how to define/use OVERLAPPING field elements
in Geant4. Fields might be either magnetic, electric or both.
field05
--------
This example demonstrates so-called "spin-frozen" condition.
field06
--------
This example exercises the new (in 9.5) capability of tracking massive
particles in a gravity field.
BlineTracer
------------
The BlineTracer module allows to trace and visualise magnetic field
lines in a Geant4 application where particle are tracked through the
magnetic field (in future, these functionalities may be integrated in
the Geant4 kernel).
examples/extended/field/field01/.README.txt
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///\file "field/field01/.README.txt"
///\brief Example field01 README page
/*! \page Examplefield01 Example field01
Example that enables investigation of the accuracy and performance of the
tracking in a magnetic field.
The key Geant4 capabilities demonstrated in this example are:
- creating a uniform magnetic field interactively using the field
messenger,
- choosing the type of Runge Kutta stepper used for integration of the
motion of charged particles in the magnetic field,
- controlling the thresholds that determine which looping particles are
killed by G4Transporation.
Some of these capabilities are available via interactive commands,
implemented in F01FieldMessenger.
The magnetic field is defined in the F01FieldSetup class which object
is created in the ConstructSDandField() function in the F01DetectorConstruction
class. The interactive commands are implemented in F01FieldMessenger.
The magnetic field is defined in F01FieldSetup, which is created in
the ConstructSDandField() method in the F01DetectorConstruction class.
\section field01_s01 Choosing the type of stepper
The basic capabilities of choosing the stepper type are demonstrated in the
field.in macro file:
\verbatim
/field/setStepperType 145 ## Choose a stepper type ( Tsito
/field/setStepperType 101 ## Choose an FSAL stepper ( FE
/field/setMinStep 0.1 mm ## Smaller steps always s
/field/update ## Initialise using parameters above
\endverbatim
In addition it is possible to choose to use a new type of stepper, known
as 'First Same as Last' or FSAL, which in each step obtains the field value
at the step endpoint and evaluates the 'right hand size' of the equation
for the next integration step. This reduces the number of calls to the field
evaluation, which can be one the most computationally expensive methods,
while providing similar accuracy.
There are several potential choices of the stepper type. Here are some suggestions:
\verbatim
===========================================================================
Number Name of Stepper Comments
===========================================================================
Recommended - default since Geant4 10.4:
15 - 'DoPri5' or
Dormand Prince 745 : Uses a pair 4th & 5th order formulae (like other 4/5
well-known and very efficient embedded method
methods); their difference is the error estimate.
Highly recommended in literature, including
Hairer & Wanner, & Numerical Recipes
Used in several established RK code (e.g. DOPRI5)
===========================================================================
Good choices for reasonably smooth fields:
45 - BogackiShampine45 : more efficient embedded 4/5 pair
Used in many applications, including
RKSUITE suite.
145 - Tsitouras45 : potentially the most efficient embedded 4/5
pair - found in expanded search of parameter
space.
56 - Dormand Prince RK56 : higher order embedded method from authors of DoPri5.
Uses a pair 5th & 6th order formulae.
78 - Dormand Prince RK78 : higher order embedded method from authors of DoPri5.
Uses a pair 7th & 8th order formulae.
9 - NystromRK4 : a specialised Nystrom method for magnetic fields.
Reuses the field value at the mid-point of the step,
and also provides an analytical estimation of the
integration error based on numerical evaluation of
fourth order variation in the equation for
magnetic field.
===========================================================================
The new 'First Same as Last' (FSAL) steppers can be chosen in addition:
1 - RKFEq1 : FSAL stepper with improved equilibrium properties.
When kinks or other anomalies are encountered,
and at the start of integration when the best
step size is not known, this type of stepper
converges faster and more smoothly to good
step sizes.
===========================================================================
The old default and old first alternative -
4 - ClassicalRK4 : original Runge-Kutta method, very robust but slower )
( obtains error estimate by doing 2 half steps )
Good baseline for comparison - long experience of use.
May be good alternative for less smooth fields.
8 - Cash Karp RKF 45 : The oldest 'embedded' RK method in Geant4 -
also fairly robust.
Faster than ClassicalRK4 for smoother fields,
as it does not need two half steps to estimate error.
Available since Geant4 1.0
===========================================================================
Other potential choices for non-smooth fields (with kinks, abrupt changes):
3 - SimpleHeum : low order, with error obtained from half-steps
23 - BogackiShampine23 : lower order embedded method (new in 10.3-beta)
===========================================================================
\endverbatim
\section field01_s02 Controlling the killing of looping particles
Occasionally tracks 'looping' in a strong magnetic field, making little
progress even over hundreds of integration steps. This is due to a
combination of a strong magnetic field and a thin material (gas or vacuum)
in which the size of a physics step is substantially larger than the radius
of curvature of the track.
Since the amount of CPU time which can be consumed by one or few such tracks
is very large, it is important to limit the number of integration steps
spent on these tracks. The module for propagation in field in Geant4
flags tracks which take more than a certain number (default 1,000) integration
steps without reaching the requested end of the step size, which was
determined by the physics and geometry.
The Geant4 G4Transportation and G4CoupledTransportation processes are tasked
to select which of the looping tracks are killed and which survive. To
balance the potential significant cost of integrating looping particles,
three thresholds exist
- **The 'Warning' Energy**: a track with energy below this value that is found to
loop is killed silently (no warning.)
Above the 'Warning Energy', if a track is selected for killing a warning is
generated.
- **The 'Important' Energy**: the threshold energy above which a track will survive
for multiple steps if found looping.
- Number of 'tracking' steps. They will be only be killed only if they still
loop after than.
**The number of 'trials'**: the number of steps that 'important' tracks survive.
Note that currently only stable particles are killed. ( Refinements to enable
toggling whether unstable particles can be killed are in development. )
This example demonstrate choosing different values for these parametes
in the main () method of field01.cc using one of two techniques.
\subsection field01_s02_sub1 i) Using G4PhysicsListHelper
The first method is new in Geant4 release 10.5, and uses the G4PhysicsListHelper
which has methods to choose a pre-selected set of parameter values. The choices
are between a set each of low and high thresholds. Either one can be enabled
by calling correspondingly
- G4PhysicsListHelper::GetPhysicsListHelper()->UseLowLooperThresholds();
or
- G4PhysicsListHelper::GetPhysicsListHelper()->UseHighLooperThresholds();
These methods must be called before the physics is constructed - i.e. typically
before RunManager's Initialise() method is called.
This works only if either
- a modular physics lists is used, or if
- the G4ModularPhysicsList and its AddTransporation method are used to create and register a common transportation process for all particles (one for each thread).
\subsection field01_s02_sub2 ii) Fine grained control (available in Geant4 versions since 7.0)
Fine grained control of the Transportation's parameters for looping particles
is also possible.
This is demonstrated in the F01RunAction::ChangeLooperParameters() method,
which is called by the BeginOfRunAction. There the appropriate
Transportation object for the electron is obtained, and its parameters
(if valid) are used to overwrite the thresholds in the G4Transportation class.
For example, to ensure that only looping particles with energy 10 keV are
killed silently we change the value of the 'Warning' Energy:
\code{.cpp}
runAction->SetWarningEnergy( 10.0 * CLHEP::keV );
\endcode
[ This is passed along to the registered G4Transportation or
G4CoupledTransportation object by the F01RunAction's ChangeLooperParameters.]
As a result the killing of any (stable) looping track with energy over 10 keV
will generate a warning.
A second configurable energy threshold enables tracks above it to survive a
chosen number of 'tracking' steps. They will be only be killed only if they
still loop after than number of tracking steps. F01RunAction's methods are
used to configure these parameters:
\code{.cpp}
runAction->SetImportantEnergy( 0.1 * CLHEP::MeV );
runAction->SetNumberOfTrials( 30 );
\endcode
which the run action passes to the G4Transportation or
G4CoupledTransportation object registered for the electron.
Note that for all pre-configured and modular physics lists share a single
Transportation process for all types of particles. So the parameters for
killing loopers will be shared by all particle types in this case.
\section field01_s1 Background Information
\subsection field01_s1_sub1 GEOMETRY DEFINITION
The "Absorber" is a solid made of a given material.
Three parameters define the absorber :
- the material of the absorber,
- the thickness of an absorber,
- the transverse size of the absorber (the input face is a square).
The volume "World" contains the "Absorber".
In this test the parameters of the "World" can be changed , too.
In addition a transverse uniform magnetic field can be applied.
The default geometry is constructed in F01DetectorConstruction class,
but all the parameters can be changed via
the commands defined in the F01DetectorMessenger class.
\subsection field01_s1_sub2 AN EVENT : THE PRIMARY GENERATOR
The primary kinematic consists of a single particle (electron, Ekin = 0.5 GeV)
which hits the
absorber perpendicular to the input face. The type of the particle
and its energy are set in the F01PrimaryGeneratorAction class, and can
be changed via the G4 build-in commands of G4ParticleGun class (see
the macros provided with this example).
It is also possible to change the position of the primary particle vertex
or activate its randomization via the commands defined in the
F01PrimaryGeneratorMessenger class.
A RUN is a set of events.
\subsection field01_s1_sub3 DETECTOR RESPONSE
The spatial distribution of charged particles transported in magnetic
field is envistigated.
A HIT is a record, event per event , of all the
informations needed to simulate and analyse the detector response.
In this example a F01CalorHit is defined as a set of 2 informations:
- the total energy deposit in the absorber,
- the total tracklength of all charged particles in the absorber,
Therefore the absorber is declared
'sensitive detector' (SD), see F01CalorimeterSD, which means they can contribute to the hit.
\subsection field01_s1_sub4 PHYSICS LIST
The particle's type and the physic processes which will be available
in this example are set in the FTFP_BERT physics list. This physics list
requires data files for electromagnetic and hadronic processes.
See more on installation of the datasets in Geant4 Installation Guide,
\subsection field01_s1_sub5 HOW TO START ?
- Execute field01 in 'batch' mode from macro file e.g.
\verbatim
% ./field01 field01.in
\endverbatim
- Execute field01 in 'interactive' mode with visualization e.g.
\verbatim
% ./field01
....
Idle> /run/beamOn 1
....
\endverbatim
*/
examples/extended/field/field01/README
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-------------------------------------------------------------------
=========================================================
Geant4 - an Object-Oriented Toolkit for Simulation in HEP
=========================================================
field01
-------
Example that enables investigation of the accuracy and performance of the
tracking in a magnetic field.
The key Geant4 capabilities demonstrated in this example are:
- creating a uniform magnetic field interactively using the field
messenger,
- choosing the type of Runge Kutta stepper used for integration of the
motion of charged particles in the magnetic field,
- controlling the thresholds that determine which looping particles are
killed by G4Transporation.
Some of these capabilities are available via interactive commands,
implemented in F01FieldMessenger.
A. The magnetic field is defined in F01FieldSetup, which is created in
the ConstructSDandField() method in the F01DetectorConstruction
class.
B. Choosing the type of stepper -
The basic capabilities of choosing the stepper type are demonstrated in the
field.in macro file:
/field/setStepperType 145 ## Choose a stepper type ( Tsitouras )
/field/setStepperType 101 ## Choose an FSAL stepper ( FEqRK1 )
/field/setMinStep 0.1 mm ## Smaller steps always succeed
/field/update ## Initialise using parameters above
In addition it is possible to choose to use a new type of stepper, known
as 'First Same as Last' or FSAL, which in each step obtains the field value
at the step endpoint and evaluates the 'right hand size' of the equation
for the next integration step. This reduces the number of calls to the field
evaluation, which can be one the most computationally expensive methods,
while providing similar accuracy.
There are several potential choices of the stepper type. Here are some
suggestions:
===========================================================================
Number Name of Stepper Comments
===========================================================================
Recommended - default since Geant4 10.4:
15 - 'DoPri5' or
Dormand Prince 745 : Uses a pair 4th & 5th order formulae (like other 4/5
well-known and very efficient embedded method
methods); their difference is the error estimate.
Highly recommended in literature, including
Hairer & Wanner, & Numerical Recipes
Used in several established RK code (e.g. DOPRI5)
===========================================================================
Good choices for reasonably smooth fields:
45 - BogackiShampine45 : more efficient embedded 4/5 pair
Used in many applications, including
RKSUITE suite.
145 - Tsitouras45 : potentially the most efficient embedded 4/5
pair - found in expanded search of parameter
space.
56 - Dormand Prince RK56 : higher order embedded method from authors of DoPri5.
Uses a pair 5th & 6th order formulae.
78 - Dormand Prince RK78 : higher order embedded method from authors of DoPri5.
Uses a pair 7th & 8th order formulae.
9 - NystromRK4 : a specialised Nystrom method for magnetic fields.
Reuses the field value at the mid-point of the step,
and also provides an analytical estimation of the
integration error based on numerical evaluation of
fourth order variation in the equation for
magnetic field.
===========================================================================
The new 'First Same as Last' (FSAL) steppers can be chosen in addition:
1 - RKFEq1 : FSAL stepper with improved equilibrium properties.
When kinks or other anomalies are encountered,
and at the start of integration when the best
step size is not known, this type of stepper
converges faster and more smoothly to good
step sizes.
===========================================================================
The old default and old first alternative -
4 - ClassicalRK4 : original Runge-Kutta method, very robust but slower )
( obtains error estimate by doing 2 half steps )
Good baseline for comparison - long experience of use.
May be good alternative for less smooth fields.
8 - Cash Karp RKF 45 : The oldest 'embedded' RK method in Geant4 -
also fairly robust.
Faster than ClassicalRK4 for smoother fields,
as it does not need two half steps to estimate error.
Available since Geant4 1.0
===========================================================================
Other potential choices for non-smooth fields (with kinks, abrupt changes):
3 - SimpleHeum : low order, with error obtained from half-steps
23 - BogackiShampine23 : lower order embedded method (new in 10.3-beta)
===========================================================================
C. Controlling the killing of looping particles
Occasionally tracks 'looping' in a strong magnetic field, making little
progress even over hundreds of integration steps. This is due to a
combination of a strong magnetic field and a thin material (gas or vacuum)
in which the size of a physics step is substantially larger than the radius
of curvature of the track.
Since the amount of CPU time which can be consumed by one or few such tracks
is very large, it is important to limit the number of integration steps
spent on these tracks. The module for propagation in field in Geant4
flags tracks which take more than a certain number (default 1,000) integration
steps without reaching the requested end of the step size, which was
determined by the physics and geometry.
The Geant4 G4Transportation and G4CoupledTransportation processes are tasked
to select which of the looping tracks are killed and which survive. To
balance the potential significant cost of integrating looping particles,
three thresholds exist
The 'Warning' Energy: a track with energy below this value that is found to
loop is killed silently (no warning.)
Above the 'Warning Energy', if a track is selected for killing a warning is
generated.
The 'Important' Energy: the threshold energy above which a track will survive
for multiple steps if found looping.
number of 'tracking' steps. They will be only be killed only if they still
loop after than
The number of 'trials': the number of steps that 'important' tracks survive.
Note that currently only stable particles are killed. ( Refinements to enable
toggling whether unstable particles can be killed are in development. )
This example demonstrate choosing different values for these parametes
in the main() method of field01.cc using one of two techniques.
The first method is new in Geant4 release 10.5, and uses the G4PhysicsListHelper
which has methods to choose a pre-selected set of parameter values. The choices
are between a set each of low and high thresholds. Either one can be enabled
by calling correspondingly
- G4PhysicsListHelper::GetPhysicsListHelper()->UseLowLooperThresholds();
or
- G4PhysicsListHelper::GetPhysicsListHelper()->UseHighLooperThresholds();
These methods must be called before the physics is constructed - i.e. typically
before RunManager's Initialise() method is called.
This works only if either
- a modular physics lists is used, or if
- the G4ModularPhysicsList and its AddTransporation method are used
to create and register a common transportation process for all particles
(one for each thread).
ii) Fine grained control (available in Geant4 versions since 7.0)
Fine grained control of the Transportation's parameters for looping particles
is also possible.
This is demonstrated in the F01RunAction's ChangeLooperParameters method,
which is called by the BeginOfRunAction. There the appropriate
Transportation object for the electron is obtained, and its parameters
(if valid) are used to overwrite the thresholds in the G4Transportation class.
For example, to ensure that only looping particles with energy 10 keV are
killed silently we change the value of the 'Warning' Energy:
runAction->SetWarningEnergy( 10.0 * CLHEP::keV );
[ This is passed along to the registered G4Transportation or
G4CoupledTransportation object by the F01RunAction's ChangeLooperParameters.]
As a result the killing of any (stable) looping track with energy over 10 keV
will generate a warning.
A second configurable energy threshold enables tracks above it to survive a
chosen number of 'tracking' steps. They will be only be killed only if they
still loop after than number of tracking steps. F01RunAction's methods are
used to configure these parameters:
runAction->SetImportantEnergy( 0.1 * CLHEP::MeV );
runAction->SetNumberOfTrials( 30 );
which the run action passes to the G4Transportation or
G4CoupledTransportation object registered for the electron.
Note that for all pre-configured and modular physics lists share a single
Transportation process for all types of particles. So the parameters for
killing loopers will be shared by all particle types in this case.
Background Information
1- GEOMETRY DEFINITION
The "Absorber" is a solid made of a given material.
Three parameters define the absorber :
- the material of the absorber,
- the thickness of an absorber,
- the transverse size of the absorber (the input face is a square).
The volume "World" contains the "Absorber".
In this test the parameters of the "World" can be changed , too.
In addition a transverse uniform magnetic field can be applied.
The default geometry is constructed in F01DetectorConstruction class,
but all the parameters can be changed via
the commands defined in the F01DetectorMessenger class.
2- AN EVENT : THE PRIMARY GENERATOR
The primary kinematic consists of a single particle (electron, Ekin = 0.5 GeV)
which hits the
absorber perpendicular to the input face. The type of the particle
and its energy are set in the F01PrimaryGeneratorAction class, and can
be changed via the G4 build-in commands of G4ParticleGun class (see
the macros provided with this example).
It is also possible to change the position of the primary particle vertex
or activate its randomization via the commands defined in the
F01PrimaryGeneratorMessenger class.
A RUN is a set of events.
3- DETECTOR RESPONSE
The spatial distribution of charged particles transported in magnetic
field is envistigated.
A HIT is a record, event per event , of all the
informations needed to simulate and analyse the detector response.
In this example a F01CalorHit is defined as a set of 2 informations:
- the total energy deposit in the absorber,
- the total tracklength of all charged particles in the absorber,
Therefore the absorber is declared
'sensitive detector' (SD), see F01CalorimeterSD, which means they can contribute to the hit.
4- PHYSICS LIST
The particle's type and the physic processes which will be available
in this example are set in the FTFP_BERT physics list. This physics list
requires data files for electromagnetic and hadronic processes.
See more on installation of the datasets in Geant4 Installation Guide,
5- HOW TO START ?
- Execute field01 in 'batch' mode from macro file e.g.
% ./field01 field01.in
- Execute field01 in 'interactive' mode with visualization e.g.
% ./field01
....
Idle> /run/beamOn 1
....
examples/extended/field/field02/.README.txt
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///\file "field/field02/.README.txt"
///\brief Example field02 README page
/*! \page Examplefield02 Example field02
Test for investigation of tracking in electric field
and field dependent electromagnetic processes.
\section field02_s0 FIELD DEFINITION
The field is a constant electric field.
Technical note: in order to use any electric field, it is
necessary to create the objects for its equation of motion,
the stepper and driver for the integration, and the
chord finder.
The class that does these is F02ElectricFieldSetup. Its object
is created in the ConstructSDandField() function in the F02DetectorConstruction
class. The interactive commands are implemented in F02FieldMessenger.
\section field02_s1 GEOMETRY DEFINITION
The "Absorber" is a solid made of a given material.
Three parameters define the absorber :
- the material of the absorber,
- the thickness of an absorber,
- the transverse size of the absorber (the input face is a square).
The volume "World" contains the "Absorber".
In this test the parameters of the "World" can be changed , too.
In addition a transverse uniform electric field can be applied.
The default geometry is constructed in F02DetectorConstruction class,
but all the parameters can be changed via
the commands defined in the F02DetectorMessenger class.
\section field02_s2 AN EVENT : THE PRIMARY GENERATOR
The primary kinematic consists of a single particle which hits the
absorber perpendicular to the input face. The type of the particle
and its energy are set in the F02PrimaryGeneratorAction class, and can
be changed via the G4 build-in commands of G4ParticleGun class (see
the macros provided with this example).
It is also possible to change the position of the primary particle vertex
or activate its randomization via the commands defined in the
F01PrimaryGeneratorMessenger class.
A RUN is a set of events.
\section field02_s3 DETECTOR RESPONSE
A HIT is a record, event per event , of all the
informations needed to simulate and analyse the detector response.
In this example a F02CalorHit is defined as a set of 2 informations:
- the total energy deposit in the absorber,
- the total tracklength of all charged particles in the absorber,
Therefore the absorber is declared
'sensitive detector' (SD), see F02CalorimeterSD, which means they can contribute to the hit.
\section field02_s4 PHYSICS LIST
The particle's type and the physic processes which will be available
in this example are set in the FTFP_BERT physics list. This physics list
requires data files for electromagnetic and hadronic processes.
See more on installation of the datasets in Geant4 Installation Guide,
\section field02_s5 HOW TO START ?
- Execute field02 in 'batch' mode from macro file e.g.
\verbatim
% ./field02 field02.in
\endverbatim
- Execute field02 in 'interactive' mode with visualization e.g.
\verbatim
% ./field02
....
Idle> /run/beamOn 1
....
\endverbatim
*/
examples/extended/field/field02/README
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-------------------------------------------------------------------
=========================================================
Geant4 - an Object-Oriented Toolkit for Simulation in HEP
=========================================================
field02
-------
Test for investigation of tracking in electric field
and field dependent electromagnetic processes.
1- FIELD DEFINITION
The field is a constant electric field.
Technical note: in order to use any electric field, it is
necessary to create the objects for its equation of motion,
the stepper and driver for the integration, and the
chord finder.
The class that does these is F02ElectricFieldSetup. Its object
is created in the ConstructSDandField() function in the F02DetectorConstruction
class. The interactive commands are implemented in F02FieldMessenger.
1- GEOMETRY DEFINITION
The "Absorber" is a solid made of a given material.
Three parameters define the absorber :
- the material of the absorber,
- the thickness of an absorber,
- the transverse size of the absorber (the input face is a square).
The volume "World" contains the "Absorber".
In this test the parameters of the "World" can be changed , too.
In addition a transverse uniform electric field can be applied.
The default geometry is constructed in F02DetectorConstruction class,
but all the parameters can be changed via
the commands defined in the F02DetectorMessenger class.
2- AN EVENT : THE PRIMARY GENERATOR
The primary kinematic consists of a single particle which hits the
absorber perpendicular to the input face. The type of the particle
and its energy are set in the F02PrimaryGeneratorAction class, and can
be changed via the G4 build-in commands of G4ParticleGun class (see
the macros provided with this example).
It is also possible to change the position of the primary particle vertex
or activate its randomization via the commands defined in the
F01PrimaryGeneratorMessenger class.
A RUN is a set of events.
3- DETECTOR RESPONSE
A HIT is a record, event per event , of all the
informations needed to simulate and analyse the detector response.
In this example a F02CalorHit is defined as a set of 2 informations:
- the total energy deposit in the absorber,
- the total tracklength of all charged particles in the absorber,
Therefore the absorber is declared
'sensitive detector' (SD), see F02CalorimeterSD, which means they can contribute to the hit.
4- PHYSICS LIST
The particle's type and the physic processes which will be available
in this example are set in the FTFP_BERT physics list. This physics list
requires data files for electromagnetic and hadronic processes.
See more on installation of the datasets in Geant4 Installation Guide,
5- HOW TO START ?
- Execute field02 in 'batch' mode from macro file e.g.
% ./field02 field02.in
- Execute field02 in 'interactive' mode with visualization e.g.
% ./field02
....
Idle> /run/beamOn 1
....
examples/extended/field/field03/.README.txt
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///\file "field/field03/.README.txt"
///\brief Example field03 README page
/*! \page Examplefield03 Example field03
Example of tracking in magnetic field where field associated
to selected logical volumes varies.
A global and a local magnetic field are defined in the F03FieldSetup class, which object
is created in the ConstructSDandField() function in the F03DetectorConstruction
class. The local magnetic field is set to the "Radiator" volume.
The interactive commands are implemented in F03FieldMessenger.
\section field03_s1 GEOMETRY DEFINITION
The "Absorber" is a solid made of a given material.
Three parameters define the absorber :
- the material of the absorber,
- the thickness of an absorber,
- the transverse size of the absorber (the input face is a square).
The volume "World" contains the "Absorber".
In this test the parameters of the "World" can be changed , too.
A transverse global uniform magnetic field can be applied.
In addition, the "Radiator" volume, which is placed in geometry next
to the absorber, has a local magnetic field.
The default geometry is constructed in F03DetectorConstruction class,
but all the parameters can be changed via
the commands defined in the F03DetectorMessenger class.
\section field03_s2 AN EVENT : THE PRIMARY GENERATOR
The primary kinematic consists of a single particle which hits the
absorber perpendicular to the input face. The type of the particle
and its energy are set in the F03PrimaryGeneratorAction class, and can
be changed via the G4 build-in commands of G4ParticleGun class (see
the macros provided with this example).
It is also possible to change the position of the primary particle vertex
or activate its randomization via the commands defined in the
F01PrimaryGeneratorMessenger class.
A RUN is a set of events.
\section field03_s3 DETECTOR RESPONSE
A HIT is a record, event per event , of all the
informations needed to simulate and analyse the detector response.
In this example a F03CalorHit is defined as a set of 2 informations:
- the total energy deposit in the absorber,
- the total tracklength of all charged particles in the absorber,
Therefore the absorber is declared
'sensitive detector' (SD), see F03CalorimeterSD, which means they can contribute to the hit.
\subsection field01_s4 PHYSICS LIST
The particle's type and the physic processes which will be available
in this example are set in the FTFP_BERT physics list. This physics list
requires data files for electromagnetic and hadronic processes.
See more on installation of the datasets in Geant4 Installation Guide,
\section field03_s5 HOW TO START ?
- Execute field03 in 'batch' mode from macro files e.g.
\verbatim
% ./field03 field03.in
\endverbatim
- Execute field03 in 'interactive' mode with visualization e.g.
\verbatim
% ./field03
....
Idle> /run/beamOn 1
....
\endverbatim
*/
examples/extended/field/field03/README
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-------------------------------------------------------------------
=========================================================
Geant4 - an Object-Oriented Toolkit for Simulation in HEP
=========================================================
field03
-------
Example of tracking in magnetic field where field associated
to selected logical volumes varies.
A global and a local magnetic field are defined in the F03FieldSetup class, which object
is created in the ConstructSDandField() function in the F03DetectorConstruction
class. The local magnetic field is set to the "Radiator" volume.
The interactive commands are implemented in F03FieldMessenger.
1- GEOMETRY DEFINITION
The "Absorber" is a solid made of a given material.
Three parameters define the absorber :
- the material of the absorber,
- the thickness of an absorber,
- the transverse size of the absorber (the input face is a square).
The volume "World" contains the "Absorber".
In this test the parameters of the "World" can be changed , too.
A transverse global uniform magnetic field can be applied.
In addition, the "Radiator" volume, which is placed in geometry next
to the absorber, has a local magnetic field.
The default geometry is constructed in F03DetectorConstruction class,
but all the parameters can be changed via
the commands defined in the F03DetectorMessenger class.
2- AN EVENT : THE PRIMARY GENERATOR
The primary kinematic consists of a single particle which hits the
absorber perpendicular to the input face. The type of the particle
and its energy are set in the F03PrimaryGeneratorAction class, and can
be changed via the G4 build-in commands of G4ParticleGun class (see
the macros provided with this example).
It is also possible to change the position of the primary particle vertex
or activate its randomization via the commands defined in the
F01PrimaryGeneratorMessenger class.
A RUN is a set of events.
3- DETECTOR RESPONSE
A HIT is a record, event per event , of all the
informations needed to simulate and analyse the detector response.
In this example a F03CalorHit is defined as a set of 2 informations:
- the total energy deposit in the absorber,
- the total tracklength of all charged particles in the absorber,
Therefore the absorber is declared
'sensitive detector' (SD), see F03CalorimeterSD, which means they can contribute to the hit.
4- PHYSICS LIST
The particle's type and the physic processes which will be available
in this example are set in the FTFP_BERT physics list. This physics list
requires data files for electromagnetic and hadronic processes.
See more on installation of the datasets in Geant4 Installation Guide,
5- HOW TO START ?
- Execute field03 in 'batch' mode from macro files e.g.
% ./field03 field03.in
- Execute field03 in 'interactive' mode with visualization e.g.
% ./field03
....
Idle> /run/beamOn 1
....
examples/extended/field/field04/.README.txt
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///\file "field/field04/.README.txt"
///\brief Example field04 README page
/*! \page Examplefield04 Example field04
This example shows how to define/use OVERLAPPING field elements
in Geant4. Fields might be either magnetic, electric or both.
Credit goes to Tom Roberts and Muons Inc. since much of the code
and ideas were taken at liberty from the (GNU GPL) source of
G4BEAMLINE release 1.12.
http://g4beamline.muonsinc.com
\section field04_s1 Classes
\subsection field04_sub_s11 main ()
See field04.cc.
The example can be run with the following optional arguments:
\verbatim
% field04 [-m macro ] [-p physicsList] [-r randomSeed] [-s preinit|idle]
\endverbatim
If a macro is provided with the option "-m", the program runs in a batch mode,
otherwise the program open the interactive session after executing the
default initialization macro init_vis.mac. The option "-s preinit" can be used
to start the program without initialization in PreInit phase.
For example:
to assign the F04PhysicsList:
\verbatim
% field04 -p QGSP_BERT
\endverbatim
an initial random number seed with:
\verbatim
% field04 field04.in -r 12345
\endverbatim
to start with a macro file and an initial seed:
\verbatim
% field04 -m field04.in -r 12345
\endverbatim
\subsection field04_sub_s12 F04DetectorConstruction
The geometry consists of two solenoidal magnets: a "CaptureMgnt"
followed by a (blue-colored "TransferMgnt". By definition, the
axis and center of the "CaptureMgnt" coincide with the "World". The
position of the "TransferMgnt" relative to the downstream end of the
"CaptureMgnt", as well as its axis angle, both may vary. A cylindrical
"Target" is positioned inside the "CaptureMgnt". Its axis can vary
from 0 to 180 deg, and hence also the direction of the incoming
proton beam wrt the "CaptureMgnt"'s axis. A "Degrader" is located
inside the "TransferMgnt", its default position being at the
upstream end of the "TransferMgnt". Finally, also a "TestPlane" is
located inside the "TransferMgnt", by default at its downstream end.
The "World" consists of a solid cylinder made of a given material.
(It is the responsibility of the user to make the world
large enough to contain the rest of the geometry!)
Three parameters define the world :
- the material of the world,
- the world radius,
- the world length.
Example (default values):
\verbatim
/field04/SetWorldMat G4_AIR
/field04/SetWorldR 5.0 m
/field04/SetWorldZ 50.0 m
\endverbatim
The "Target" is a solid cylinder made of a given material.
Five parameters define the target:
- the material of the target,
- the target radius,
- the target thickness,
- the target position inside the "CaptureMgnt",
- the target axis angle relative to that of the "CaptureMgnt".
Example (default values):
\verbatim
/field04/SetTgtMat G4_W
/field04/SetTgtRad 0.4 cm
/field04/SetTgtThick 16.0 cm
/field04/SetTgtPos 0.0 cm
/field04/SetTgtAng 170
\endverbatim
The "Degrader" is a solid cylinder made of a given material.
Four parameters define the degrader:
- the material of the degrader,
- the degrader radius,
- the degrader thickness,
- the degrader position relative to the "TransferMgnt" center.
Example (default values):
\verbatim
/field04/SetDgrMat G4_Pb
/field04/SetDgrRad 30.0 cm
/field04/SetDgrThick 0.1 cm
#/field04/SetDgrPos -7.4 m
\endverbatim
The "CaptureMgnt" is a solenoid (vacuum cylinder). It is either
a two-sided or a one-sided magnetic bottle with the B field
varying linearly from the center value B1 to the edge value B2.
The one-sided F04FocusSolenoid has the open end at +z and focuses
on the z < 0 side.
Four parameters define the "CaptureMgnt":
- the magnet radius,
- the magnet length,
- the weaker magnetic field at the center B1
- the stronger magnetic field at the edge B2
Example (default values):
\verbatim
/field04/SetCaptureR 0.6 m
/field04/SetCaptureZ 4.0 m
/field/SetCaptureB1 2.5 tesla
/field/SetCaptureB2 5.0 tesla
\endverbatim
The "TransferMgnt" is a solenoid (vacuum cylinder) with a
constant B-field. When the "TransferMgnt" follows immediately
the "CaptureMgnt", its relative position is at 0 cm.
Four parameters define the "TransferMgnt":
- the magnet radius,
- the magnet length,
- the magnet field,
- the magnet relative position
(its upstream face wrt the downstream face of the "CaptureMgnt".)
Example (default values):
\verbatim
/field04/SetTransferR 0.3 m
/field04/SetTransferZ 15.0 m
/field/SetTransferB 5.0 tesla
/field04/SetTransferP 0.0 m
\endverbatim
The default geometry is constructed in F04DetectorConstruction class,
but all the parameters can be changed via the commands defined in
the F04DetectorMessenger class.
\subsection field04_sub_s13 F04Materials
Material definitions are done through the singleton class F04Materials
which keeps a pointer to the G4NistManager. It has a method
GetMaterial by name (G4String) which in turn invokes the
G4NistManager::FindOrBuildMaterial, and/or G4Material::GetMaterial
methods. It has also a method CreateMaterials which, for materials
absent from the NIST data base, shows how to create them using the
G4NistManager::ConstructNewMaterial method.
\subsection field04_sub_s14 F04PrimaryGeneratorAction
The primary kinematic consists of a single particle which hits the
target perpendicular to its upstream face. The type of the particle
and its energy are set in the F04PrimaryGeneratorAction class, and can
be changed via the G4 build-in commands of the G4ParticleGun class.
In addition, there is a fRndmFlag, which once set allows the beam to
explore randomly the whole cross section of the target. The default
beam consists of 500 MeV protons, starting at the upstream face of
the target, directed along dx = dy = 0, dz = 1 wrt the target frame.
The default direction should NOT be changed! The arguments of the
x/y/zvertex commands are relative to the target center.
Example:
\verbatim
/gun/random on
#/gun/xvertex 0 mm
#/gun/yvertex 0 mm
#/gun/zvertex -100 mm
\endverbatim
\subsection field04_sub_s15 DETECTOR RESPONSE in F04SteppingAction
Information is extracted from the program via F04SteppingAction
at the TestPlane.
\subsection field04_sub_s16 F04PhysicsList
The F04PhysicsList extends a selected Geant4 physics list.
The base physics list name is provided by its name in the F04PhysicsList
constructor.
In addition to processes defined in the base Geant4 physics list,
there is added the F04StepMax process and the decay of pions can be assigned
via dedicated commands in F04PhysicsListMessenger.
The command to define maximum step:
\verbatim
/exp/phys/stepMax value unit
\endverbatim
The decay of pions can be assigned via (pi -> e nu, pi -> mu nu):
\verbatim
/decay/pienu
/decay/pimunu
\endverbatim
The pienu assignment includes a small fraction of radiative decay:
e nu gamma (G4PionRadiativeDecayChannel).
The standard/default muon decay chain is modified to be 98.6%
G4MuonDecayChannelWithSpin and 1.4% G4MuonRadiativeDecayChannelWithSpin
in ConstructParticle().
The pion decay process G4PolDecay inherits from G4Decay and implements
the virtual method - empty in the base class - DaughterPolarization
The muon decay process is G4DecayWithSpin
Furthermore, the following commands are also available, but
may only be used AFTER /run/initialize
\verbatim
/process/inactivate msc
/process/activate msc
\endverbatim
\subsection field04_sub_s17 Overlapping Fields
The F04GlobalField (a singleton) is instantiated in
F04DetectorConstruction() and assigned to the global field manager
in UpdateField():
\verbatim
fFieldManager = GetGlobalFieldManager();
fFieldManager->SetDetectorField(this);
\endverbatim
The F04GlobalField has a std::vector<ElementField*> FieldList
The field from each individual beamline element is given by a
F04ElementField object. Any number of overlapping F04ElementField
objects can be added to the F04GlobalField. Any element that
represents an element with an EM field must add the appropriate
F04ElementField to the global F04GlobalField object.
Of course, the F04GlobalField has the method GetFieldValue implemented.
Before /run/initialize in the macro file or command, the update
field command must have been issued if any of the other following
field commands was employed:
\verbatim
/field/update
\endverbatim
Other options are:
\verbatim
/field/setStepperType 4
/field/setMinStep 10 mm
/field/setDeltaChord 3.0 mm
/field/setDeltaOneStep 0.01 mm
/field/setDeltaIntersection 0.1 mm
/field/setEpsMin 2.5e-7 mm
/field/setEpsMax 0.05 mm
\endverbatim
Each field element has a rectilinear bounding box in global
coordinate space which is checked before a point is verified to
actually be inside the F04ElementField (IsWithin and IsOutside).
SetGlobalPoint is called 8 times for the corners of the local
bounding box, after a local->global coordinate transform.
The F04ElementField is the interface class used by F04GlobalField to
compute the field value at a given point[].
A beamline element, for example the F04SimpleSolenoid, will derive
from F04ElementField and implement the computation for the element.
\verbatim
simpleSolenoid
= new F04SimpleSolenoid(B, l, logicTransferMgnt,TransferMgntCenter);
\endverbatim
Besides the magnetic field and the length of the simple solenoid,
the constructor needs the knowledge of the G4LogicalVolume for
the beamline element and where its center is located in the
'World'.
The F04ElementField has a G4AffineTransform "fGlobal2local" which
allows the quick computation of coordinate transformations. It can
only be determined by knowing the element's coordinate origin in
the global frame and after all of the geometry has been defined.
For this reason, the object is prepared in two stages, through the
constructor providing it with the coordinate center and a pointer
to the G4LogicalVolume. Later the Construct() method is called to
calculate the fGlobal2local and the bounding box. This can be done
from the F04RunAction::BeginOfRunAction method, for only then are we
certain that the geometry has been completely built:
\verbatim
FieldList* fields = F04GlobalField::GetObject()->GetFields();
if (fields) {
if (fields->size()>0) {
FieldList::iterator i;
for (i=fields->begin(); i!=fields->end(); ++i)(*i)->Construct();
}
}
\endverbatim
The F04ElementField constructor will also add the derived object into
F04GlobalField. Finally, its AddFieldValue() will add the field value
for this element to field[].
\subsection field04_sub_s18 User Action Classes
- F04RunActionMessenger:
\verbatim
/rndm/save freq - to save rndm status in external files
0 not saved
>0 saved on: beginOfRun.rndm
1 saved on: endOfRun.rndm
2 saved on: endOfEvent.rndm
/rndm/read random/run0evt8268.rndm
\endverbatim
- F04RunAction: \n
BeginOfRunAction: Deal with random number storage,
initialization etc. Call the Construct() method of
F04ElementFields in the FieldList of F04GlobalField object.
EndOfRunAction: random number storage/status printing.
- F04EventActionMessenger: \n
\verbatim
/event/setverbose
\endverbatim
- F04EventAction(F04RunAction* RA): \n
Customized BeginOfEvent printing
EndofEvent:
saveEngingStatus and showEngineStatus according to flag
in F04RunAction
- F04TrackingAction: \n
PreUserTrackingAction: Instantiate F04UserTrackInformation
and set the application TrackStatus.
PostUserTrackingAction: Retreive F04UserTrackInformation
and decide to save random number status accordingly.
- F04SteppingActionMessenger: \n
- F04SteppingAction: \n
UserSteppingAction: Kill primary if/when outside Target
volume. Diagnostic/histogram filling for particles at a
TestPlane. Find decay position and when particle
FIRST reverses z-momentum component via using a
F04UserTrackInformation object.
- F04StackingAction: \n
Track only primaries, pi+ or mu+
- F04UserTrackInformation: \n
Keep an application F04TrackStatus for the track: \n
undefined, left, right, reverse
- F04SteppingVerbose: \n
Only print track header and step information for
pi+ and mu+.
Note: the information for primary protons is not printed.
- F04Trajectory, F04TrajectoryPoint: \n
Example of application specific implementations
\section field04_s2 HOW TO START ?
- Execute field04 in 'batch' mode from macro files e.g.
\verbatim
% field04 -m field04.in
\endverbatim
- Execute field04 in 'interactive' mode with visualization
\verbatim
% field04
....
Idle> type your commands
....
\endverbatim
- Execute field04 in 'interactive' mode without initialization
\verbatim
% field04 -s preinit
....
Idle> type your commands, then
Idle> /run/initialize
Idle> /control/execute vis.mac
....
\endverbatim
*/
examples/extended/field/field04/README
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=========================================================
Geant4 - an Object-Oriented Toolkit for Simulation in HEP
=========================================================
field04 Example
---------------
This example shows how to define/use OVERLAPPING field elements
in Geant4. Fields might be either magnetic, electric or both.
Credit goes to Tom Roberts and Muons Inc. since much of the code
and ideas were taken at liberty from the (GNU GPL) source of
G4BEAMLINE release 1.12.
http://g4beamline.muonsinc.com
**************
*Classes Used*
**************
1 - main()
See field04.cc.
The example can be run with the following optional arguments:
% field04 [-m macro ] [-p physicsList] [-r randomSeed] [-s preinit|idle]
If a macro is provided with the option "-m", the program runs in a batch mode,
otherwise the program open the interactive session after executing the
default initialization macro init_vis.mac. The option "-s preinit" can be used
to start the program without initialization in PreInit phase.
For example:
to assign the F04PhysicsList:
% field04 -p QGSP_BERT
an initial random number seed with:
% field04 field04.in -r 12345
to start with a macro file and an initial seed:
% field04 -m field04.in -r 12345
2- GEOMETRY DEFINITION
The geometry consists of two solenoidal magnets: a "CaptureMgnt"
followed by a (blue-colored "TransferMgnt". By definition, the
axis and center of the "CaptureMgnt" coincide with the "World". The
position of the "TransferMgnt" relative to the downstream end of the
"CaptureMgnt", as well as its axis angle, both may vary. A cylindrical
"Target" is positioned inside the "CaptureMgnt". Its axis can vary
from 0 to 180 deg, and hence also the direction of the incoming
proton beam wrt the "CaptureMgnt"'s axis. A "Degrader" is located
inside the "TransferMgnt", its default position being at the
upstream end of the "TransferMgnt". Finally, also a "TestPlane" is
located inside the "TransferMgnt", by default at its downstream end.
The "World" consists of a solid cylinder made of a given material.
(It is the responsibility of the user to make the world
large enough to contain the rest of the geometry!)
Three parameters define the world :
- the material of the world,
- the world radius,
- the world length.
Example (default values):
/field04/SetWorldMat G4_AIR
/field04/SetWorldR 5.0 m
/field04/SetWorldZ 50.0 m
The "Target" is a solid cylinder made of a given material.
Five parameters define the target:
- the material of the target,
- the target radius,
- the target thickness,
- the target position inside the "CaptureMgnt",
- the target axis angle relative to that of the "CaptureMgnt".
Example (default values):
/field04/SetTgtMat G4_W
/field04/SetTgtRad 0.4 cm
/field04/SetTgtThick 16.0 cm
/field04/SetTgtPos 0.0 cm
/field04/SetTgtAng 170
The "Degrader" is a solid cylinder made of a given material.
Four parameters define the degrader:
- the material of the degrader,
- the degrader radius,
- the degrader thickness,
- the degrader position relative to the "TransferMgnt" center.
Example (default values):
/field04/SetDgrMat G4_Pb
/field04/SetDgrRad 30.0 cm
/field04/SetDgrThick 0.1 cm
#/field04/SetDgrPos -7.4 m
The "CaptureMgnt" is a solenoid (vacuum cylinder). It is either
a two-sided or a one-sided magnetic bottle with the B field
varying linearly from the center value B1 to the edge value B2.
The one-sided F04FocusSolenoid has the open end at +z and focuses
on the z < 0 side.
Four parameters define the "CaptureMgnt":
- the magnet radius,
- the magnet length,
- the weaker magnetic field at the center B1
- the stronger magnetic field at the edge B2
Example (default values):
/field04/SetCaptureR 0.6 m
/field04/SetCaptureZ 4.0 m
/field/SetCaptureB1 2.5 tesla
/field/SetCaptureB2 5.0 tesla
The "TransferMgnt" is a solenoid (vacuum cylinder) with a
constant B-field. When the "TransferMgnt" follows immediately
the "CaptureMgnt", its relative position is at 0 cm.
Four parameters define the "TransferMgnt":
- the magnet radius,
- the magnet length,
- the magnet field,
- the magnet relative position
(its upstream face wrt the downstream face of the "CaptureMgnt".)
Example (default values):
/field04/SetTransferR 0.3 m
/field04/SetTransferZ 15.0 m
/field/SetTransferB 5.0 tesla
/field04/SetTransferP 0.0 m
The default geometry is constructed in F04DetectorConstruction class,
but all the parameters can be changed via the commands defined in
the F04DetectorMessenger class.
3- MATERIAL DEFINITION
Material definitions are done through the singleton class F04Materials
which keeps a pointer to the G4NistManager. It has a method
GetMaterial by name (G4String) which in turn invokes the
G4NistManager::FindOrBuildMaterial, and/or G4Material::GetMaterial
methods. It has also a method CreateMaterials which, for materials
absent from the NIST data base, shows how to create them using the
G4NistManager::ConstructNewMaterial method.
4- AN EVENT: THE PRIMARY GENERATOR
The primary kinematic consists of a single particle which hits the
target perpendicular to its upstream face. The type of the particle
and its energy are set in the F04PrimaryGeneratorAction class, and can
be changed via the G4 build-in commands of the G4ParticleGun class.
In addition, there is a fRndmFlag, which once set allows the beam to
explore randomly the whole cross section of the target. The default
beam consists of 500 MeV protons, starting at the upstream face of
the target, directed along dx = dy = 0, dz = 1 wrt the target frame.
The default direction should NOT be changed! The arguments of the
x/y/zvertex commands are relative to the target center.
Example:
/gun/random on
#/gun/xvertex 0 mm
#/gun/yvertex 0 mm
#/gun/zvertex -100 mm
5- DETECTOR RESPONSE
Information is extracted from the program via F04SteppingAction
at the TestPlane.
6- PHYSICS
The F04PhysicsList extends a selected Geant4 physics list.
The base physics list name is provided by its name in the F04PhysicsList
constructor.
In addition to processes defined in the base Geant4 physics list,
there is added the F04StepMax process and the decay of pions can be assigned
via dedicated commands in F04PhysicsListMessenger.
The command to define maximum step:
/exp/phys/stepMax value unit
The decay of pions can be assigned via (pi -> e nu, pi -> mu nu):
/decay/pienu
/decay/pimunu
The pienu assignment includes a small fraction of radiative decay:
e nu gamma (G4PionRadiativeDecayChannel).
The standard/default muon decay chain is modified to be 98.6%
G4MuonDecayChannelWithSpin and 1.4% G4MuonRadiativeDecayChannelWithSpin
in ConstructParticle().
The pion decay process G4PolDecay inherits from G4Decay and implements
the virtual method - empty in the base class - DaughterPolarization
The muon decay process is G4DecayWithSpin
Furthermore, the following commands are also available, but
may only be used AFTER /run/initialize
/process/inactivate msc
/process/activate msc
7- Overlapping Fields
The F04GlobalField (a singleton) is instantiated in
F04DetectorConstruction() and assigned to the global field manager
in UpdateField():
fFieldManager = GetGlobalFieldManager();
fFieldManager->SetDetectorField(this);
The F04GlobalField has a std::vector<ElementField*> FieldList
The field from each individual beamline element is given by a
F04ElementField object. Any number of overlapping F04ElementField
objects can be added to the F04GlobalField. Any element that
represents an element with an EM field must add the appropriate
F04ElementField to the global F04GlobalField object.
Of course, the F04GlobalField has the method GetFieldValue implemented.
Before /run/initialize in the macro file or command, the update
field command must have been issued if any of the other following
field commands was employed:
/field/update
Other options are:
/field/setStepperType 4
/field/setMinStep 10 mm
/field/setDeltaChord 3.0 mm
/field/setDeltaOneStep 0.01 mm
/field/setDeltaIntersection 0.1 mm
/field/setEpsMin 2.5e-7 mm
/field/setEpsMax 0.05 mm
Each field element has a rectilinear bounding box in global
coordinate space which is checked before a point is verified to
actually be inside the F04ElementField (IsWithin and IsOutside).
SetGlobalPoint is called 8 times for the corners of the local
bounding box, after a local->global coordinate transform.
The F04ElementField is the interface class used by F04GlobalField to
compute the field value at a given point[].
A beamline element, for example the F04SimpleSolenoid, will derive
from F04ElementField and implement the computation for the element.
simpleSolenoid
= new F04SimpleSolenoid(B, l, logicTransferMgnt,TransferMgntCenter);
Besides the magnetic field and the length of the simple solenoid,
the constructor needs the knowledge of the G4LogicalVolume for
the beamline element and where its center is located in the
'World'.
The F04ElementField has a G4AffineTransform "fGlobal2local" which
allows the quick computation of coordinate transformations. It can
only be determined by knowing the element's coordinate origin in
the global frame and after all of the geometry has been defined.
For this reason, the object is prepared in two stages, through the
constructor providing it with the coordinate center and a pointer
to the G4LogicalVolume. Later the Construct() method is called to
calculate the fGlobal2local and the bounding box. This can be done
from the F04RunAction::BeginOfRunAction method, for only then are we
certain that the geometry has been completely built:
FieldList* fields = F04GlobalField::GetObject()->GetFields();
if (fields) {
if (fields->size()>0) {
FieldList::iterator i;
for (i=fields->begin(); i!=fields->end(); ++i)(*i)->Construct();
}
}
The F04ElementField constructor will also add the derived object into
F04GlobalField. Finally, its AddFieldValue() will add the field value
for this element to field[].
8- User Action Classes
F04RunActionMessenger:
/rndm/save freq - to save rndm status in external files
0 not saved
>0 saved on: beginOfRun.rndm
1 saved on: endOfRun.rndm
2 saved on: endOfEvent.rndm
/rndm/read random/run0evt8268.rndm
F04RunAction:
BeginOfRunAction: Deal with random number storage,
initialization etc. Call the Construct() method of
F04ElementFields in the FieldList of F04GlobalField object.
EndOfRunAction: random number storage/status printing.
F04EventActionMessenger:
/event/setverbose
F04EventAction(RunAction* RA):
Customized BeginOfEvent printing
EndofEvent:
saveEngingStatus and showEngineStatus according to flag
in F04RunAction
F04TrackingAction:
PreUserTrackingAction: Instantiate F04UserTrackInformation
and set the application TrackStatus.
PostUserTrackingAction: Retreive F04UserTrackInformation
and decide to save random number status accordingly.
F04SteppingActionMessenger:
F04SteppingAction:
UserSteppingAction: Kill primary if/when outside Target
volume. Diagnostic/histogram filling for particles at a
TestPlane. Find decay position and when particle
FIRST reverses z-momentum component via using a
F04UserTrackInformation object.
F04StackingAction:
Track only primaries, pi+ or mu+
F04UserTrackInformation:
Keep an application F04TrackStatus for the track:
undefined, left, right, reverse
F04SteppingVerbose:
Only print track header and step information for
pi+ and mu+.
Note: the information for primary protons is not printed.
F04Trajectory, TrajectoryPoint:
Example of application specific implementations
9- HOW TO START ?
- Execute field04 in 'batch' mode from macro files e.g.
% field04 -m field04.in
- Execute field04 in 'interactive' mode with visualization
% field04
....
Idle> type your commands
....
- Execute field04 in 'interactive' mode without initialization
% field04 -s preinit
....
Idle> type your commands, then
Idle> /run/initialize
Idle> /control/execute vis.mac
....
examples/extended/field/field04/random/README
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Directory including files generated during run for
storing seeds.
examples/extended/field/field05/.README.txt
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///\file "field/field05/.README.txt"
///\brief Example field05 README page
/*! \page Examplefield05 Example field05
This example checks so-called "spin-frozen" condition
There is a good example article hep-ph/0012087v1.
This article discusses about how to cancel the muon g-2 precession by
applying an electric field.
- 1) beta is muon velocity,
- 2) B is an uniform magnetic field and vec{beta}.vec{B}=0,
"." means scalar product,
- 3) Radial electric field (E) in the lab frame and vec{beta}.vec{E}=0,
- 4) a=(g-2)/2 is muon anomalous magnetic moment.
The required electric field to cancel the g-2 precession is,
\verbatim
E=a*B*light_c*gamma**2*beta.
\endverbatim
In case of gamma=5 and B=0.24 Tesla, the required electric field is
\verbatim
E=2 MV/m.
\endverbatim
"Spin-frozen" happens when spin rotation cycle and muon rotation cycle
are same. In this case, both cycles should be 149.5 nsec.
See also:
http://research.kek.jp/people/hiromi/MyHomePage/G-2_work_files/SpinStudyinEMfieldByGeant4.pdf
Credit goes to Hiromi Iinuma from KEK.
Classes Used
\section field05_s1 main ()
See field05.cc.
\section field05_s2 GEOMETRY DEFINITION
as simple world G4Box with a G4ElectroMagneticField \n
propagating both spin and momentum (G4EqEMFieldWithSpin) \n
with G4ClassicalRK4(fEquation,12) and \n
Bz = 0.24*tesla; \n
Er = 2.113987E+6*volt/m;
\section field05_s3 AN EVENT: THE PRIMARY GENERATOR
use mu+ G4ParticleGun with Pmu = 517.6*MeV/c \n
and aligned spin and momentum direction
\section field05_s4 PHYSICS
\verbatim
RegisterPhysics(new G4SpinDecayPhysics());
RegisterPhysics(new G4StepLimiterPhysics());
G4SpinDecayPhysics defines muon decay modes with spin,
G4StepLimiterPhysics defines G4StepLimiter and G4UserSpecialCuts.
\section field05_s5 User Action Classes
SteppingAction: \n
G4Exception when the cosine of the angle between
the spin and the momentum is < (1.-1.E-7)
\section field05_s6 HOW TO START ?
- Execute field05 in 'batch' mode from macro files e.g.
\verbatim
% field05 field05.in > field.out &
\endverbatim
- Execute field05 in 'interactive' mode with visualization e.g.
\verbatim
% field05
....
Idle> type your commands, for example:
Idle> run/beamOn 1
....
\endverbatim
*/
examples/extended/field/field05/README
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=========================================================
Geant4 - an Object-Oriented Toolkit for Simulation in HEP
=========================================================
field05 Example
---------------
This example checks so-called "spin-frozen" condition
There is a good example article hep-ph/0012087v1.
This article discusses about how to cancel the muon g-2 precession by
applying an electric field.
1) beta is muon velocity,
2) B is an uniform magnetic field and \vec{beta}.\vec{B}=0,
"." means scalar product,
3) Radial electric field (E) in the lab frame and \vec{beta}.\vec{E}=0,
4) a=(g-2)/2 is muon anomalous magnetic moment.
The required electric field to cancel the g-2 precession is,
E=a*B*light_c*gamma**2*beta.
In case of gamma=5 and B=0.24 Tesla, the required electric field is
E=2 MV/m.
"Spin-frozen" happens when spin rotation cycle and muon rotation cycle
are same. In this case, both cycles should be 149.5 nsec.
See also:
http://research.kek.jp/people/hiromi/MyHomePage/G-2_work_files/SpinStudyinEMfieldByGeant4.pdf
Credit goes to Hiromi Iinuma from KEK.
**************
*Classes Used*
**************
1 - main()
See field05.cc.
2- GEOMETRY DEFINITION
as simple world G4Box with a G4ElectroMagneticField
propagating both spin and momentum (G4EqEMFieldWithSpin)
with G4ClassicalRK4(fEquation,12) and
Bz = 0.24*tesla;
Er = 2.113987E+6*volt/m;
3- AN EVENT: THE PRIMARY GENERATOR
use mu+ G4ParticleGun with Pmu = 517.6*MeV/c
and aligned spin and momentum direction
4- PHYSICS
RegisterPhysics(new G4SpinDecayPhysics());
RegisterPhysics(new G4StepLimiterPhysics());
G4SpinDecayPhysics defines muon decay modes with spin,
G4StepLimiterPhysics defines G4StepLimiter and G4UserSpecialCuts.
5- User Action Classes
SteppingAction:
G4Exception when the cosine of the angle between
the spin and the momentum is < (1.-1.E-7)
6- HOW TO START ?
- Execute field05 in 'batch' mode from macro files e.g.
% field05 field05.in > field.out &
- Execute field05 in 'interactive' mode with visualization e.g.
% field05
....
Idle> type your commands, for example:
Idle> run/beamOn 1
....
examples/extended/field/field06/.README.txt
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///\file "field/field06/.README.txt"
///\brief Example field06 README page
/*! \page Examplefield06 Example field06
This example exercises the capability of tracking massive
particles in a gravity field.
Credit goes to Erik Miller (Univ. of Northern British Columbia) and
Garry Yan (Univ. of Toronto)
Classes Used
\section field06_s1 main()
See field06.cc.
\section field06_s2 GEOMETRY DEFINITION
As simple world G4Box with a G4UniformGravityField propagating momentum
(G4EqGravityField) with G4ClassicalRK4(fEquation,8). The example uses the
default gravity field on the earth's surface: gy = -9.81*m/s/s/c_light.
\section field06_s3 AN EVENT: THE PRIMARY GENERATOR
Uses an Ultra Cold Neutron (UCN) and G4ParticleGun with: \n
particleEnergy = G4UniformRand()*1e-7*eV
UCN are launched from (0,0,0) uniform into 4pi
\section field06_s4 PHYSICS
The simulation knows of only six particles: G4Neutron, G4Proton,
G4Electron, G4AntiNeutrinoE, G4MuonPlus and G4MuonMinus
\verbatim
RegisterPhysics(new G4StepLimiterPhysics());
\endverbatim
G4StepLimiterPhysics defines G4StepLimiter and G4UserSpecialCuts
\section field06_s5 HOW TO START ?
This example handles the program arguments in a new way.
It can be run with the following optional arguments:
\verbatim
% field06 [-m macro ] [-u UIsession] [-t nThreads] [-r randomSeed]
\endverbatim
The -t option is available only in multi-threading mode
and it allows the user to override the Geant4 default number of
threads. The number of threads can be also set via G4FORCENUMBEROFTHREADS
environment variable which has the top priority.
- Execute field06 in 'batch' mode from macro files e.g.
\verbatim
% field06 -m field06.in > field06.out &
\endverbatim
- Execute field06 in 'interactive' mode with visualization e.g.
\verbatim
% field06
....
Idle> type your commands, for example:
Idle> run/beamOn 1
....
\endverbatim
*/
examples/extended/field/field06/README
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=========================================================
Geant4 - an Object-Oriented Toolkit for Simulation in HEP
=========================================================
field06 Example
---------------
This example exercises the capability of tracking massive
particles in a gravity field.
Credit goes to Erik Miller (Univ. of Northern British Columbia) and
Garry Yan (Univ. of Toronto)
**************
*Classes Used*
**************
1 - main()
See field06.cc.
2- GEOMETRY DEFINITION
As simple world G4Box with a G4UniformGravityField propagating momentum
(G4EqGravityField) with G4ClassicalRK4(fEquation,8). The example uses the
default gravity field on the earth's surface: gy = -9.81*m/s/s/c_light.
3- AN EVENT: THE PRIMARY GENERATOR
Uses an Ultra Cold Neutron (UCN) and G4ParticleGun with:
particleEnergy = G4UniformRand()*1e-7*eV
UCN are launched from (0,0,0) uniform into 4pi
4- PHYSICS
The simulation knows of only six particles: G4Neutron, G4Proton,
G4Electron, G4AntiNeutrinoE, G4MuonPlus and G4MuonMinus
RegisterPhysics(new G4StepLimiterPhysics());
G4StepLimiterPhysics defines G4StepLimiter and G4UserSpecialCuts
5- HOW TO START ?
This example handles the program arguments in a new way.
It can be run with the following optional arguments:
% field06 [-m macro ] [-u UIsession] [-t nThreads] [-r randomSeed]
The -t option is available only in multi-threading mode
and it allows the user to override the Geant4 default number of
threads. The number of threads can be also set via G4FORCENUMBEROFTHREADS
environment variable which has the top priority.
- Execute field06 in 'batch' mode from macro files e.g.
% field06 -m field06.in > field06.out &
- Execute field06 in 'interactive' mode with visualization e.g.
% field06
....
Idle> type your commands, for example:
Idle> run/beamOn 1
....