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electron stuck on volume boundary with (local) uniform magnetic field 

Forum: Fields: Magnetic and Otherwise
Date: 21 Jul, 2008
From: Brian Fisher <Brian Fisher>

I'm experiencing a situation similar to posting #96 in this forum. That thread seems to have gone dead, so I'm posting a new thread. I'm using Geant4 9.1p02 In a very simple setup, electrons sometimes are "bouncing" between a volume (with a local magnetic field) and its mother (which does not have a magnetic field). Both volumes are filled with "vacuum." I get many (tens of thousands) of messages like these: WARNING - G4Navigator::ComputeStep() Track stuck, not moving for 10 steps in volume -expHall- at point (-8.257550732,-9.52505,18.49195399) direction: (-0.01057780492,7.285534641e-05,0.9999440508). Potential geometry or navigation problem ! Trying pushing it of 9e-10 mm ... I've been modeling charged particle detector telescopes, and in the process of hunting this problem down, I have reduced the geometry of my problem to: 1) a 1x1x1 m^3 box filled with vacuum. This is the "expHall" volume 2) a "BFieldZone" box also filled with vacuum with the following parameters: Solid type: G4Box Parameters: half length X: 1.39526 cm half length Y: 0.952505 cm half length Z: 0.952505 cm ----------------------------------------------------------- Center of Box: X = 0 cm Y = 0 cm Z = 1.98525 cm 3) the "BFieldZone" box has a uniform 2 kilogauss magnetic field in the +X direction. This is how I've defined the (local) magnetic field for the "BFieldZone" volume: G4double = fFieldValue = 2.0*kilogauss; fMagField = new G4UniformMagField(G4ThreeVector(fFieldValue, 0.0, 0.0)); fEquation = new G4Mag_UsualEqRhs(fMagField); fStepper = new G4ExactHelixStepper(fEquation); fIntgrDriver = new G4MagInt_Driver(1.0*micrometer, fStepper, fStepper->GetNumberOfVariables(), 2); fChordFinder = new G4ChordFinder(fIntgrDriver); fFieldMgr = new G4FieldManager(fMagField, fChordFinder); logicBFieldZone->SetFieldManager(fFieldMgr, true); 4) The "expHall" box has no magnetic field. When I turn the tracking verbosity up to 2, the 'offending' event looks like this: ********************************************************************************************************* * G4Track Information: Particle = e-, Track ID = 1, Parent ID = 0 ********************************************************************************************************* Step# X Y Z KineE dEStep StepLeng TrakLeng Volume Process 0 -8.06 mm -9.69 mm 7.87e-55 fm 1.97 MeV 0 eV 0 fm 0 fm expHall initStep 1 -8.25 mm -9.53 mm 1.81 cm 1.97 MeV4.82e-19 eV 1.81 cm 1.81 cm expHall Transportation 2 -8.25 mm -9.53 mm 1.81 cm 1.97 MeV 0 eV 0 fm 1.81 cm physiBFieldZone Transportation 3 -8.25 mm -9.53 mm 1.81 cm 1.97 MeV 0 eV 0 fm 1.81 cm expHall Transportation 4 -8.25 mm -9.53 mm 1.81 cm 1.97 MeV 0 eV 0 fm 1.81 cm physiBFieldZone Transportation 5 -8.25 mm -9.53 mm 1.81 cm 1.97 MeV 0 eV 0 fm 1.81 cm expHall Transportation 6 -8.25 mm -9.53 mm 1.81 cm 1.97 MeV 0 eV 0 fm 1.81 cm physiBFieldZone Transportation 7 -8.25 mm -9.53 mm 1.81 cm 1.97 MeV 0 eV 0 fm 1.81 cm expHall Transportation 8 -8.25 mm -9.53 mm 1.81 cm 1.97 MeV 0 eV 0 fm 1.81 cm physiBFieldZone Transportation 9 -8.25 mm -9.53 mm 1.81 cm 1.97 MeV 0 eV 0 fm 1.81 cm expHall Transportation 10 -8.25 mm -9.52 mm 1.82 cm 1.97 MeV2.39e-21 eV 89.9 um 1.82 cm physiBFieldZone Transportation 11 -8.25 mm -9.53 mm 1.82 cm 1.97 MeV1.91e-22 eV 7.16 um 1.82 cm physiBFieldZone Transportation 12 -8.25 mm -9.53 mm 1.82 cm 1.97 MeV 0 eV 0 fm 1.82 cm expHall Transportation 13 -8.25 mm -9.53 mm 1.82 cm 1.97 MeV 0 eV 0 fm 1.82 cm physiBFieldZone Transportation 14 -8.25 mm -9.53 mm 1.82 cm 1.97 MeV 0 eV 0 fm 1.82 cm expHall Transportation 15 -8.25 mm -9.53 mm 1.82 cm 1.97 MeV 0 eV 0 fm 1.82 cm physiBFieldZone Transportation 16 -8.25 mm -9.53 mm 1.82 cm 1.97 MeV 0 eV 0 fm 1.82 cm expHall Transportation 17 -8.25 mm -9.53 mm 1.82 cm 1.97 MeV 0 eV 0 fm 1.82 cm physiBFieldZone Transportation 18 -8.25 mm -9.53 mm 1.82 cm 1.97 MeV 0 eV 0 fm 1.82 cm expHall Transportation 19 -8.25 mm -9.53 mm 1.82 cm 1.97 MeV 0 eV 0 fm 1.82 cm physiBFieldZone Transportation 20 -8.25 mm -9.53 mm 1.82 cm 1.97 MeV 0 eV 0 fm 1.82 cm expHall Transportation 21 -8.26 mm -9.52 mm 1.83 cm 1.97 MeV2.39e-21 eV 89.9 um 1.83 cm physiBFieldZone Transportation 22 -8.26 mm -9.53 mm 1.83 cm 1.97 MeV1.32e-22 eV 4.96 um 1.83 cm physiBFieldZone Transportation 23 -8.26 mm -9.53 mm 1.83 cm 1.97 MeV 0 eV 0 fm 1.83 cm expHall Transportation 24 -8.26 mm -9.53 mm 1.83 cm 1.97 MeV 0 eV 0 fm 1.83 cm physiBFieldZone Transportation 25 -8.26 mm -9.53 mm 1.83 cm 1.97 MeV 0 eV 0 fm 1.83 cm expHall Transportation 26 -8.26 mm -9.53 mm 1.83 cm 1.97 MeV 0 eV 0 fm 1.83 cm physiBFieldZone Transportation [and so on, seemingly forever] If the verbosity is turned up to 3, I get this: [snip] #Step# X Y Z KineE dEStep StepLeng TrakLeng Volume Process 30132 -8.26 mm -9.53 mm 1.85 cm 1.97 MeV 0 eV 0 fm 1.85 cm physiBFieldZone Transportation >>AlongStepDoIt (after all invocations): ++List of invoked processes 1) Transportation 2) msc 3) eIoni 4) eBrem ++G4Step Information Address of G4Track : 0x3046970 Step Length (mm) : 0 Energy Deposit (MeV) : 0 ----------------------------------------------------------------------- StepPoint Information PreStep PostStep ----------------------------------------------------------------------- Position - x (mm) : -8.257551022101929 -8.257551022101929 Position - y (mm) : -9.52505 -9.52505 Position - z (mm) : 18.49198141201282 18.49198141201282 Global Time (ns) : 0.06304591361302052 0.06304591361302052 Local Time (ns) : 0.06304591361302052 0.06304591361302052 Proper Time (ns) : 0.01300913309755812 0.01300913309755812 Momentum Direct - x : -0.01057780492354854-0.01057780492354854 Momentum Direct - y : 7.285445476253925e-057.285445476253925e-05 Momentum Direct - z : 0.9999440508024575 0.9999440508024575 Momentum - x (MeV/c): -0.02563161644372119-0.02563161644372119 Momentum - y (MeV/c): 0.00017653733021041490.0001765373302104149 Momentum - z (MeV/c): 2.423015224859268 2.423015224859268 Total Energy (MeV) : 2.476444998409542 2.476444998409542 Kinetic Energy (MeV): 1.965445938409542 1.965445938409542 Velocity (mm/ns) : 293.3407906754122 293.3407906754122 Volume Name : expHall expHall Safety (mm) : 5e-10 5e-10 Polarization - x : 0 0 Polarization - y : 0 0 Polarization - Z : 0 0 Weight : 1 1 Step Status : Geom Limit Geom Limit Process defined Step: Transportation Transportation ----------------------------------------------------------------------- ++List of secondaries generated (x,y,z,kE,t,PID): No. of secodaries = 0 **PostStepDoIt (after all invocations): ++List of invoked processes 1) Transportation 2) msc 3) eIoni (Forced) ++G4Step Information Address of G4Track : 0x3046970 Step Length (mm) : 0 Energy Deposit (MeV) : 0 ----------------------------------------------------------------------- StepPoint Information PreStep PostStep ----------------------------------------------------------------------- Position - x (mm) : -8.257551022101929 -8.257551022101929 Position - y (mm) : -9.52505 -9.52505 Position - z (mm) : 18.49198141201282 18.49198141201282 Global Time (ns) : 0.06304591361302052 0.06304591361302052 Local Time (ns) : 0.06304591361302052 0.06304591361302052 Proper Time (ns) : 0.01300913309755812 0.01300913309755812 Momentum Direct - x : -0.01057780492354854-0.01057780492354854 Momentum Direct - y : 7.285445476253925e-057.285445476253925e-05 Momentum Direct - z : 0.9999440508024575 0.9999440508024575 Momentum - x (MeV/c): -0.02563161644372119-0.02563161644372119 Momentum - y (MeV/c): 0.00017653733021041490.0001765373302104149 Momentum - z (MeV/c): 2.423015224859268 2.423015224859268 Total Energy (MeV) : 2.476444998409542 2.476444998409542 Kinetic Energy (MeV): 1.965445938409542 1.965445938409542 Velocity (mm/ns) : 293.3407906754122 293.3407906754122 Volume Name : expHall physiBFieldZone Safety (mm) : 5e-10 5e-10 Polarization - x : 0 0 Polarization - y : 0 0 Polarization - Z : 0 0 Weight : 1 1 Step Status : Geom Limit Geom Limit Process defined Step: Transportation Transportation ----------------------------------------------------------------------- ++List of secondaries generated (x,y,z,kE,t,PID): No. of secodaries = 0 [Note]Secondaries from AlongStepDoIt included. #Step# X Y Z KineE dEStep StepLeng TrakLeng Volume Process 30133 -8.26 mm -9.53 mm 1.85 cm 1.97 MeV 0 eV 0 fm 1.85 cm expHall Transportation >>AlongStepDoIt (after all invocations): ++List of invoked processes 1) Transportation 2) msc 3) eIoni 4) eBrem ++G4Step Information Address of G4Track : 0x3046970 Step Length (mm) : 0 Energy Deposit (MeV) : 0 ----------------------------------------------------------------------- StepPoint Information PreStep PostStep ----------------------------------------------------------------------- Position - x (mm) : -8.257551022101929 -8.257551022101929 Position - y (mm) : -9.52505 -9.52505 Position - z (mm) : 18.49198141201282 18.49198141201282 Global Time (ns) : 0.06304591361302052 0.06304591361302052 Local Time (ns) : 0.06304591361302052 0.06304591361302052 Proper Time (ns) : 0.01300913309755812 0.01300913309755812 Momentum Direct - x : -0.01057780492354854-0.01057780492354854 Momentum Direct - y : 7.285445476253925e-057.285445476253925e-05 Momentum Direct - z : 0.9999440508024575 0.9999440508024575 Momentum - x (MeV/c): -0.02563161644372119-0.02563161644372119 Momentum - y (MeV/c): 0.00017653733021041490.0001765373302104149 Momentum - z (MeV/c): 2.423015224859268 2.423015224859268 Total Energy (MeV) : 2.476444998409542 2.476444998409542 Kinetic Energy (MeV): 1.965445938409542 1.965445938409542 Velocity (mm/ns) : 293.3407906754122 293.3407906754122 Volume Name : physiBFieldZone physiBFieldZone Safety (mm) : 5e-10 5e-10 Polarization - x : 0 0 Polarization - y : 0 0 Polarization - Z : 0 0 Weight : 1 1 Step Status : Geom Limit Geom Limit Process defined Step: Transportation Transportation ----------------------------------------------------------------------- ++List of secondaries generated (x,y,z,kE,t,PID): No. of secodaries = 0 **PostStepDoIt (after all invocations): ++List of invoked processes 1) Transportation 2) msc 3) eIoni (Forced) ++G4Step Information Address of G4Track : 0x3046970 Step Length (mm) : 0 Energy Deposit (MeV) : 0 ----------------------------------------------------------------------- StepPoint Information PreStep PostStep ----------------------------------------------------------------------- Position - x (mm) : -8.257551022101929 -8.257551022101929 Position - y (mm) : -9.52505 -9.52505 Position - z (mm) : 18.49198141201282 18.49198141201282 Global Time (ns) : 0.06304591361302052 0.06304591361302052 Local Time (ns) : 0.06304591361302052 0.06304591361302052 Proper Time (ns) : 0.01300913309755812 0.01300913309755812 Momentum Direct - x : -0.01057780492354854-0.01057780492354854 Momentum Direct - y : 7.285445476253925e-057.285445476253925e-05 Momentum Direct - z : 0.9999440508024575 0.9999440508024575 Momentum - x (MeV/c): -0.02563161644372119-0.02563161644372119 Momentum - y (MeV/c): 0.00017653733021041490.0001765373302104149 Momentum - z (MeV/c): 2.423015224859268 2.423015224859268 Total Energy (MeV) : 2.476444998409542 2.476444998409542 Kinetic Energy (MeV): 1.965445938409542 1.965445938409542 Velocity (mm/ns) : 293.3407906754122 293.3407906754122 Volume Name : physiBFieldZone expHall Safety (mm) : 5e-10 5e-10 Polarization - x : 0 0 Polarization - y : 0 0 Polarization - Z : 0 0 Weight : 1 1 Step Status : Geom Limit Geom Limit Process defined Step: Transportation Transportation ----------------------------------------------------------------------- ++List of secondaries generated (x,y,z,kE,t,PID): No. of secodaries = 0 [Note]Secondaries from AlongStepDoIt included. #Step# X Y Z KineE dEStep StepLeng TrakLeng Volume Process 30134 -8.26 mm -9.53 mm 1.85 cm 1.97 MeV 0 eV 0 fm 1.85 cm physiBFieldZone Transportation [and so on... ] So I'm wondering why is my step length at the boundary being set to zero? Do I have a bad set of physics lists? Is the fact that this particle is nearly perpendicular to the field the problem? Any help anyone can provide is GREATLY appreciated. Thanks, Brian

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