
///\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

*/
