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Forum: Fields: Magnetic and Otherwise
Date: 25 Feb, 2016
From: sauvestre <sauvestre>

Hello, I am doing a simulation in which i have defined a uniform magnetic field Bz

along the Oz axis within a box made of vacuum. The box is 10*10*10 cm³.

I am launching electrons with various energies and different incidence angles.

I was really surprised to see that if the energy is lower than a "given"

incident energy the track length in the box varies according to the primary

electron energy. As i told, my box is made of vacuum which means that there is

no slowing down. In order to illustrate this trend, i have attached three

snapshots of the electron trajectory in the box at three different energies

having a fixed incident angle at the entrance of the box. The electron

comes from the right in the figures.

The magnitude of the field along the z axis is 20 Tesla (pretty big) but the

same behavior is observed if lower magnetic field amplitudes are used. As one

can see, whereas the electron exists the box for a 50 MeV primary incident

energy this is no more the case for 5 and 1 MeV. Moreover, as the incident

energy decreases, the projected track length and the total track length

decrease as well. I don't understand this point at all.

I am using the following implementation in my DetectorConstruction:

  G4double fieldValueX = 0.*tesla;
  G4double fieldValueY = 0.*tesla;
  G4double fieldValueZ = 20.*tesla;

  G4UniformMagField* Field 
  = new G4UniformMagField(G4ThreeVector(fieldValueX,fieldValueY,fieldValueZ));

  G4Mag_UsualEqRhs* Equation = new G4Mag_UsualEqRhs(Field);

  G4MagIntegratorStepper* Stepper = new G4ClassicalRK4(Equation, 8);

  G4ChordFinder* ChordFinder = new G4ChordFinder(Field,0.01*mm,Stepper);

  G4FieldManager* fieldMgr = new G4FieldManager(Field,ChordFinder);

// Set accuracy parameters

  G4double deltaChord        = 0.001*mm;
  ChordFinder->SetDeltaChord( deltaChord );
  G4double deltaOneStep      = 0.001*mm; 
  fieldMgr->SetAccuraciesWithDeltaOneStep(deltaOneStep); 
  G4double deltaIntersection = 0.001*mm;
  fieldMgr->SetDeltaIntersection(deltaIntersection);

Attached are the snapshots for one electron at a given incident angle

and three initial incident energies:

50 MeV, 5 MeV and 1 MeV. Bz=20 Tesla

Thanks in advance for any lightening.

Regards

JES

PS: geant4-version : geant4.10.0

   Attachment:
      http://hypernews.slac.stanford.edu/HyperNews/geant4/get/AUX/2016/02/25/01.47-80529-proton1MeV.pdf
      http://hypernews.slac.stanford.edu/HyperNews/geant4/get/AUX/2016/02/25/01.48-1115-proton5MeV.pdf
      http://hypernews.slac.stanford.edu/HyperNews/geant4/get/AUX/2016/02/25/01.48-21610-proton50MeV.pdf

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1 Idea: Re: pb using Magnetic field in vacuum. Track length depends on incident energy   (sauvestre - 25 Feb, 2016)
1 Question: Re: pb using Magnetic field in vacuum. Track length depends on incident energy   (sauvestre - 25 Feb, 2016)
1 Feedback: Re: pb using Magnetic field in vacuum. Track length depends on incident energy   (Gumplinger Peter - 26 Feb, 2016)
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2 Feedback: Re: pb using Magnetic field in vacuum. Track length depends on incident energy   (Gumplinger Peter - 26 Feb, 2016)
1 Ok: Re: pb using Magnetic field in vacuum. Track length depends on incident energy   (sauvestre - 26 Feb, 2016)
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