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     Geant4 - an Object-Oriented Toolkit for Simulation in HEP
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                            TestEm16
                            --------
      Simulate synchrotron radiation
	
 1- GEOMETRY DEFINITION

     The geometry consists of a single block of a homogenous material.

     Two parameters define the geometry :
 	- the material of the box,
	- the (full) size of the box.
     The default is 500 m of vacuum.

     A transverse uniform magnetic field can be applied.

     The default geometry is constructed in DetectorConstruction class,
     but all of the above parameters can be changed interactively via
     the commands defined in the DetectorMessenger class.

 2- PHYSICS LIST

     The particle list include EM processes for gamma, e+, e-, mu+, mu-,
     and protons, for the rest of particles only transportation. 
     Synchrotron radiation is added to all charged particles.
     To make the synchrotron radiation easily visible, a very low
     pressure "vaccuum" and a magnetic field of by default 1 Tesla
     in z-direction is used.

 3- AN EVENT : THE PRIMARY GENERATOR

     The primary kinematic consists of a single particle which hits the
     block perpendicular to the input face. The type of the particle
     and its energy are set in the PrimaryGeneratorAction class, and can
     changed via the G4 build-in commands of ParticleGun class (see
     the macros provided with this example).
     The default is an positron of 10 GeV.
     	
     In addition one can choose randomly the impact point of the incident
     particle. The corresponding interactive command is built in
     PrimaryGeneratorMessenger class.
	 	
     A RUN is a set of events.


 4- VISUALIZATION

     The Visualization Manager is set in the main().
     The initialisation of the drawing is done via the command
     > /control/execute vis.mac
     > /run/beamOn 1

     The detector has a default view which is a longitudinal view of the box.

     The tracks are drawn at the end of event, and erased at the end of run.
     Optionaly one can choose to draw all particles, only the charged one,
     or none. This command is defined in EventActionMessenger class.

 5- PHYSICS DEMO

     The particle's type and the physic processes which will be available
     in this example are set in PhysicsList class.

     In addition a build-in interactive command (/process/inactivate proname)
     allows to activate/inactivate the processes one by one.

     The threshold for producing secondaries can be changed.
     eg: /run/setCut 100 micrometer
         /run/initialize
	
     To visualize the Synchrotron radiation :
	 /control/execute vis.mac
		  	
 6- HOW TO START ?

     - execute Test  in 'batch' mode from macro files
 	% TestEm16    run01.mac

     - execute Test  in 'interactive mode' with visualization
 	% TestEm16
 		....
 	Idle> type your commands
 		....
 	Idle> exit
  
    other Macros provided in this example:
      - run01_prot.mac
        Synchrotron radiation of 50 TeV protons in 20 T field
        relevant for FCC-hh
      - run02.mac
        weak field long distance example
        relevant for space applications
      - TestReflection.mac
        specular reflection of X-ray gammas on a block of
        copper defined by Box_1m_Cu.gdml

 7 - TRACKING : stepMax and setMaxStepLength

  In order to control the accuracy of the deposition, the user can limit
  'by hand' the maximum  step size stepMax of charged particles.

  The maximum tracking step length for computing of magnetic field lines
  is by default set to 1 km.
  Synchrotron radiation in very weak magnetic fields of the order of 1 Gauss
  may require longer pathlength.
  This can be achieved with using setMaxStepLength like
  /testem/tracking/setMaxStepLength 100 km

8- HISTOGRAMS

  TestEm16 produces 3 histograms which illustrate synchrotron radiation.
  The photon energy spectrum (photons / energy bin) and the power spectrum
  (photon spectrum weighted with the photon energy) and a histogram
  of the path length between photon radiation is produced.
	 
  The histograms are managed by G4AnalysisManager and its Messenger.
     	
  The histos can be activated individually with the command :
  /analysis/h1/set id nbBins valMin valMax unit
  where 'unit' is the desired unit for the histo (MeV or KeV, cm or mm, etc..)
								  
  One can control the name of the histograms file with the command:
  /analysis/setFileName  name  (default testem16)
   
  It is possible to choose the format of the histogram file : root (default),
  xml, csv, by using namespace in HistoManager.hh 	
   
  It is also possible to print selected histograms on an ascii file:
  /analysis/h1/setAscii id
  All selected histos will be written on a file name.ascii  (default testem16)
