|Message: pb using Magnetic field in vacuum. Track length depends on incident energy||Not Logged In (login)|
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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.
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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