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None Uniform magnetic field using the G4GlobalMagFieldMessenger 

Forum: Fields: Magnetic and Otherwise
Date: 19 Feb, 2018
From: <heid>

Hi

I am trying to simulate (with Geant4 10.4 and multithreading) a uniform magnetic field using the G4GlobalMagFieldMessenger in my ConstructSDandField method of DetectorConstruction.cc (see code below) and the UIcommand /globalField/setValue 0 1.5 0 tesla in my input file. My problem is that I would like to modify the accuracy of the fMinStep transport parameter, but I am having difficulty with this.

Looking at the Geant4 TestEM examples, I cannot work out how to access and manipulate the G4ChordFinder set in the G4GlobalMagFieldMessenger within my ConstructSDandField method of DetectorConstruction.cc in order to change the value of fMinStep.

I am new to Geant4 and am hoping that someone could please steer me in the right direction.

--------------------------------------------------------------------------------
G4ThreadLocal G4GlobalMagFieldMessenger* DetectorConstruction::fMagFieldMsg = 0;
G4ThreadLocal G4UniformMagField* DetectorConstruction::MagField = 0;        
G4ThreadLocal G4FieldManager* DetectorConstruction::fieldMgr = 0;
void DetectorConstruction::ConstructSDandField()
{
  // Only called by Master thread
  std::ios::fmtflags mode = G4cout.flags();
  G4cout.setf(std::ios::fixed,std::ios::floatfield);

  //Define a global uniform magnetic field
  if (!fMagFieldMsg)
    { 
      //--- Set value of accuracy parameters ------------------------------
      G4double minEps        = 5.0e-5;    // Minimum & value for smallest steps
      G4double maxEps        = 5.0e-5;    // Maximum & value for largest steps
      G4double delta_onestep = 1.0*micrometer; // 1.0 micrometer
      G4double miss_distance = 1.0*micrometer;
      G4double delta_intsect = 1.0*micrometer;
      G4double fMinStep      = 1.0*nm;    // minimal step of 1nm
      G4double fMaxStep      = 1.0e12;   
      G4MagIntegratorStepper* stepper = 0;//G4 default stepper

      //--- Create global magnetic field messenger. 
      //Uniform magnetic field AUTO created when field is non-zero.
      G4ThreeVector fieldValue = G4ThreeVector();
      fMagFieldMsg = new G4GlobalMagFieldMessenger(fieldValue);
      fMagFieldMsg->SetVerboseLevel(1);

      //Get value of Magnetic field from global magnetic field messenger.
      G4ThreeVector magField =  fMagFieldMsg->GetFieldValue();

      G4FieldManager *fieldMgr;
      G4TransportationManager *transportMgr =
                      G4TransportationManager::GetTransportationManager();
      fieldMgr = transportMgr->GetFieldManager();
      //fieldMgr->SetDetectorField(magField);
      //fieldMgr->CreateChordFinder(magField)

      transportMgr->GetPropagatorInField()->SetLargestAcceptableStep(fMaxStep);

      fieldMgr->SetMinimumEpsilonStep( minEps );
      fieldMgr->SetMaximumEpsilonStep( maxEps );
      fieldMgr->SetDeltaOneStep( delta_onestep );  // 0.5 micrometer
      fieldMgr->GetChordFinder()->SetDeltaChord( miss_distance );
      fieldMgr->SetDeltaIntersection( delta_intsect );
      //fieldMgr->SetChordFinder(fChordFinder);

      //Register the field messenger for deleting
      G4AutoDelete::Register(fMagFieldMsg);
   }
}
--------------------------------------------------------------------------------

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1 None: Re: Uniform magnetic field using the G4GlobalMagFieldMessenger   (Eric Simiele - 04 Apr, 2018)
(_ None: Re: Uniform magnetic field using the G4GlobalMagFieldMessenger   (heid - 05 Apr, 2018)
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