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Problem with very small stepsize caused by transportation process? 

Keywords: small stepsize, transportation
Forum: Fast Simulation, Transportation & Others
Date: 10 Jan, 2007
From: Henning Gast <Henning Gast>

Hi, I am simulating a cosmic-ray detector in G4.8.2 and have encountered the following problem: In some (1/1000) events, there is a very tiny step size in one of my "TrdLayer" volumes, leading to the event being practically stuck, for example: (description continues below) ********************************************************************************************************* * G4Track Information: Particle = e-, Track ID = 391, Parent ID = 319 ********************************************************************************************************* Step# X(mm) Y(mm) Z(mm) KinE(MeV) dE(MeV) StepLeng TrackLeng NextVolume ProcName 0 132 262 -136 2.93 0 0 0 TrdRadiator initStep 1 134 265 -125 2.81 0.122 11.3 11.3 TrdRadiator msc 2 134 265 -125 2.8 0.00425 0.535 11.9 TrdRadiator msc 3 134 265 -125 2.8 0.00012 0.00768 11.9 TrdModule Transportation 4 135 265 -124 2.8 0.000112 1.35 13.2 TrdModule msc 5 136 265 -123 2.8 0.000321 1.35 14.6 TrdModule msc 6 137 265 -122 2.8 8.46e-05 1.35 16 TrdModule msc 7 137 265 -122 2.8 4.34e-05 0.138 16.1 TrdStrawTubeWall2 Transportation 8 137 265 -122 2.78 0.0224 0.135 16.2 TrdStrawTubeWall2 msc 9 137 265 -122 2.75 0.025 0.135 16.4 TrdStrawTubeWall2 msc 10 137 265 -121 2.74 0.0143 0.075 16.4 TrdStrawTubeWall2 msc 11 137 265 -121 2.74 0 0.00011 16.4 TrdStrawTubeGas2 Transportation 12 138 266 -121 2.74 0.000465 1.08 17.5 TrdStrawTubeGas2 msc 13 139 266 -120 2.74 3.31e-05 1.08 18.6 TrdStrawTubeGas2 msc 14 140 266 -120 2.74 8.01e-05 1.08 19.7 TrdStrawTubeGas2 msc 15 141 266 -119 2.74 2.18e-05 1.06 20.7 TrdStrawTubeGas2 msc 16 141 266 -119 2.74 1.4e-05 0.188 20.9 TrdStrawTubeGas2 msc 17 141 266 -119 2.74 0 0.0078 20.9 TrdStrawTubeWall2 Transportation 18 142 266 -119 2.59 0.151 0.28 21.2 TrdStrawTubeWall2 msc 19 142 266 -119 2.52 0.0693 0.28 21.5 TrdStrawTubeWall2 msc 20 142 266 -119 2.51 0.00798 0.0414 21.5 TrdStrawTubeGas2 Transportation 21 145 267 -119 2.51 0.000523 3.56 25.1 TrdStrawTubeGas2 msc 22 148 269 -120 2.51 0.000431 3.56 28.6 TrdStrawTubeGas2 msc 23 150 271 -123 2.51 0.000999 3.56 32.2 TrdStrawTubeGas2 msc 24 151 271 -123 2.51 0.000195 0.529 32.7 TrdStrawTubeWall2 Transportation 25 151 271 -123 2.5 0.00469 0.0242 32.8 TrdStrawTubeWall2 msc 26 151 271 -123 2.5 0.00342 0.0242 32.8 TrdStrawTubeWall2 msc 27 151 271 -123 2.5 0.00262 0.0242 32.8 TrdStrawTubeWall2 msc 28 151 271 -123 2.49 0.00219 0.017 32.8 TrdStrawTubeWall2 msc 29 151 271 -123 2.49 3.8e-07 1.72e-06 32.8 TrdModule Transportation 30 151 271 -123 2.49 0.000203 0.677 33.5 TrdModule msc 31 151 272 -124 2.49 1.66e-05 0.677 34.2 TrdModule msc 32 152 272 -124 2.49 2.13e-05 0.677 34.8 TrdModule msc 33 152 272 -125 2.49 1.75e-05 0.525 35.4 TrdRadiator Transportation 34 154 278 -132 2.41 0.084 9.2 44.6 TrdRadiator msc 35 151 282 -139 2.31 0.103 9.2 53.8 TrdRadiator msc 36 144 286 -143 2.22 0.0882 9.1 62.9 TrdRadiator msc 37 136 291 -142 2.13 0.0881 9.2 72.1 TrdRadiator msc 38 129 293 -136 2.05 0.0843 9.2 81.3 TrdRadiator msc 39 127 297 -128 1.95 0.0997 9.2 90.5 TrdRadiator msc 40 129 299 -125 1.91 0.0342 4.19 94.7 TrdRadiator msc 41 130 300 -125 1.9 0.00977 0.987 95.6 TrdRadiator msc 42 130 300 -125 1.9 0.000779 0.055 95.7 TrdRadiator msc 43 130 300 -125 1.9 9.59e-07 9.4e-05 95.7 TrdModule Transportation 44 130 300 -125 1.9 0 0.267 96 TrdModule msc 45 130 300 -124 1.9 0 0.267 96.2 TrdModule msc 46 130 300 -124 1.9 9.27e-06 0.0642 96.3 TrdStrawTubeWall7 Transportation 47 130 300 -124 1.9 0.0062 0.0328 96.3 TrdStrawTubeWall7 msc 48 130 300 -124 1.89 0.00481 0.0328 96.4 TrdStrawTubeWall7 msc 49 130 300 -124 1.88 0.0121 0.0328 96.4 TrdStrawTubeWall7 msc 50 130 300 -124 1.87 0.00599 0.0328 96.4 TrdStrawTubeWall7 msc 51 130 300 -124 1.87 0.00671 0.0328 96.5 TrdStrawTubeWall7 msc 52 130 300 -124 1.86 0.00223 0.0102 96.5 TrdStrawTubeWall7 msc 53 130 300 -124 1.86 4.3e-06 1.93e-05 96.5 TrdStrawTubeGas7 Transportation 54 130 301 -124 1.86 0.000166 0.436 96.9 TrdStrawTubeGas7 msc 55 130 301 -124 1.86 0.000733 0.436 97.3 TrdStrawTubeGas7 msc 56 131 301 -124 1.86 0.000134 0.436 97.8 TrdStrawTubeGas7 msc 57 131 301 -124 1.86 0.000116 0.162 97.9 TrdStrawTubeGas7 eIoni 58 131 302 -124 1.86 8.8e-05 0.183 98.1 TrdStrawTubeWall7 Transportation 59 131 302 -124 1.84 0.0169 0.0992 98.2 TrdStrawTubeWall7 msc 60 131 302 -124 1.83 0.0147 0.0992 98.3 TrdStrawTubeWall7 msc 61 131 302 -124 1.81 0.0176 0.0992 98.4 TrdStrawTubeWall7 msc 62 131 302 -124 1.81 0.00361 0.017 98.4 TrdModule Transportation 63 131 303 -124 1.81 5.91e-05 0.84 99.3 TrdModule msc 64 132 303 -124 1.81 0.000893 0.84 100 TrdModule msc 65 132 304 -123 1.81 4.51e-05 0.67 101 TrdModule msc 66 132 304 -123 1.81 1.06e-06 0.00734 101 TrdStrawTubeWall8 Transportation 67 132 304 -123 1.79 0.0139 0.0532 101 TrdStrawTubeWall8 msc 68 132 304 -123 1.78 0.0129 0.0532 101 TrdStrawTubeWall8 msc 69 132 304 -123 1.78 0.00086 0.0081 101 TrdStrawTubeWall8 msc 70 132 304 -123 1.78 9.78e-07 4.4e-06 101 TrdStrawTubeGas8 Transportation 71 134 306 -124 1.78 0.000717 3.11 104 TrdStrawTubeGas8 msc 72 135 308 -124 1.78 0.000352 1.57 106 TrdStrawTubeWall8 Transportation 73 135 308 -124 1.77 0.0134 0.0751 106 TrdStrawTubeWall8 msc 74 135 308 -124 1.75 0.0148 0.0658 106 TrdModule Transportation 75 136 308 -124 1.75 6.12e-05 0.917 107 TrdModule msc 76 136 309 -124 1.75 0.0001 0.917 108 TrdModule msc 77 136 309 -124 1.75 0 0.22 108 TrdLongStiffener3 Transportation 78 137 309 -124 1.73 0.0259 0.0991 108 TrdLongStiffener3 msc 79 137 309 -124 1.68 0.0412 0.0902 108 TrdModule Transportation 80 137 310 -125 1.68 0 0.574 109 TrdModule msc 81 137 310 -125 1.68 6.89e-05 0.447 109 TrdRadiator Transportation 82 143 322 -135 1.47 0.161 16.9 126 TrdRadiator eIoni 83 141 329 -143 1.33 0.145 11.3 137 TrdRadiator msc 84 138 331 -144 1.29 0.0385 3.32 141 TrdRadiator msc 85 135 334 -144 1.25 0.0424 5.04 146 TrdRadiator msc 86 134 351 -131 1.05 0.197 21.2 167 TrdRadiator msc 87 137 351 -126 0.998 0.0537 6.19 173 TrdRadiator msc 88 138 351 -125 0.985 0.0132 1.47 175 TrdRadiator msc 89 139 351 -125 0.982 0.00315 0.404 175 TrdRadiator msc 90 139 351 -125 0.982 2.46e-05 0.00647 175 TrdModule Transportation 91 139 351 -125 0.982 0.000123 0.526 175 TrdModule msc 92 140 352 -124 0.982 9.75e-06 0.526 176 TrdModule msc 93 140 352 -124 0.982 0 0.213 176 TrdStrawTubeWall15 Transportation 94 140 352 -124 0.954 0.0275 0.153 176 TrdStrawTubeWall15 msc 95 140 352 -124 0.9 0.0538 0.153 177 TrdStrawTubeWall15 msc 96 140 352 -124 0.887 0.0137 0.0531 177 TrdModule Transportation 97 140 352 -124 0.887 7.62e-05 0.351 177 TrdModule msc 98 141 352 -125 0.886 3.12e-05 0.351 177 TrdModule msc 99 141 352 -125 0.886 0 0.11 177 TrdRadiator Transportation 100 142 353 -128 0.846 0.0408 4.08 181 TrdRadiator msc 101 141 352 -132 0.805 0.0406 4.08 186 TrdRadiator msc 102 139 352 -135 0.763 0.0417 4.08 190 TrdRadiator msc 103 135 352 -136 0.724 0.0398 4.08 194 TrdRadiator msc 104 132 352 -134 0.677 0.0468 4.08 198 TrdRadiator msc 105 130 353 -130 0.63 0.0467 4.08 202 TrdRadiator msc 106 131 353 -127 0.586 0.0443 4.08 206 TrdRadiator msc 107 134 353 -126 0.555 0.0303 3.35 209 TrdRadiator msc 108 136 353 -129 0.513 0.0428 4.08 213 TrdRadiator msc 109 134 353 -132 0.468 0.0448 2.99 216 TrdRadiator msc 110 134 353 -132 0.467 0.000904 0.0512 216 TrdRadiator msc 111 134 354 -132 0.467 3.81e-08 3.16e-06 216 TrdLayer Transportation 112 128 355 -128 0.466 0.00138 9.91 226 TrdLayer msc 113 130 356 -125 0.464 0.00111 3.66 230 TrdLayer msc 114 131 356 -125 0.464 0.00065 1.13 231 TrdLayer msc 115 131 356 -125 0.464 4.4e-05 0.471 232 TrdLayer msc 116 131 356 -125 0.464 2.08e-05 0.124 232 TrdLayer Transportation 117 131 356 -125 0.464 1.69e-13 1.02e-09 232 TrdLayer Transportation 118 131 356 -125 0.464 1.66e-13 1e-09 232 TrdLayer Transportation 119 131 356 -125 0.464 1.69e-13 1.02e-09 232 TrdLayer Transportation 120 131 356 -125 0.464 1.66e-13 1e-09 232 TrdLayer Transportation 121 131 356 -125 0.464 1.69e-13 1.02e-09 232 TrdLayer Transportation 122 131 356 -125 0.464 1.66e-13 1e-09 232 TrdLayer Transportation 123 131 356 -125 0.464 1.69e-13 1.02e-09 232 TrdLayer Transportation 124 131 356 -125 0.464 1.66e-13 1e-09 232 TrdLayer Transportation 125 131 356 -125 0.464 1.69e-13 1.02e-09 232 TrdLayer Transportation 126 131 356 -125 0.464 1.66e-13 1e-09 232 TrdLayer Transportation 127 131 356 -125 0.464 1.69e-13 1.02e-09 232 TrdLayer Transportation 128 131 356 -125 0.464 7.58e-13 4.58e-09 232 TrdLayer Transportation 129 131 356 -125 0.464 1.69e-13 1.02e-09 232 TrdLayer Transportation 130 131 356 -125 0.464 1.66e-13 1e-09 232 TrdLayer Transportation 131 131 356 -125 0.464 1.69e-13 1.02e-09 232 TrdLayer Transportation 132 131 356 -125 0.464 1.66e-13 1e-09 232 TrdLayer Transportation 133 131 356 -125 0.464 1.69e-13 1.02e-09 232 TrdLayer Transportation 134 131 356 -125 0.464 1.66e-13 1e-09 232 TrdLayer Transportation 135 131 356 -125 0.464 1.69e-13 1.02e-09 232 TrdLayer Transportation 136 131 356 -125 0.464 1.66e-13 1e-09 232 TrdLayer Transportation 137 131 356 -125 0.464 1.69e-13 1.02e-09 232 TrdLayer Transportation 138 131 356 -125 0.464 1.66e-13 1e-09 232 TrdLayer Transportation 139 131 356 -125 0.464 1.69e-13 1.02e-09 232 TrdLayer Transportation 140 131 356 -125 0.464 7.58e-13 4.58e-09 232 TrdLayer Transportation 141 131 356 -125 0.464 1.69e-13 1.02e-09 232 TrdLayer Transportation 142 131 356 -125 0.464 1.66e-13 1e-09 232 TrdLayer Transportation 143 131 356 -125 0.464 1.69e-13 1.02e-09 232 TrdLayer Transportation 144 131 356 -125 0.464 1.66e-13 1e-09 232 TrdLayer Transportation 145 131 356 -125 0.464 1.69e-13 1.02e-09 232 TrdLayer Transportation 146 131 356 -125 0.464 1.66e-13 1e-09 232 TrdLayer Transportation 147 131 356 -125 0.464 1.69e-13 1.02e-09 232 TrdLayer Transportation 148 131 356 -125 0.464 1.66e-13 1e-09 232 TrdLayer Transportation 149 131 356 -125 0.464 1.69e-13 1.02e-09 232 TrdLayer Transportation 150 131 356 -125 0.464 1.66e-13 1e-09 232 TrdLayer Transportation 151 131 356 -125 0.464 1.69e-13 1.02e-09 232 TrdLayer Transportation 152 131 356 -125 0.464 7.58e-13 4.58e-09 232 TrdLayer Transportation 153 131 356 -125 0.464 1.69e-13 1.02e-09 232 TrdLayer Transportation 154 131 356 -125 0.464 1.66e-13 1e-09 232 TrdLayer Transportation 155 131 356 -125 0.464 1.69e-13 1.02e-09 232 TrdLayer Transportation 156 131 356 -125 0.464 1.66e-13 1e-09 232 TrdLayer Transportation 157 131 356 -125 0.464 1.69e-13 1.02e-09 232 TrdLayer Transportation 158 131 356 -125 0.464 1.66e-13 1e-09 232 TrdLayer Transportation 159 131 356 -125 0.464 1.69e-13 1.02e-09 232 TrdLayer Transportation 160 131 356 -125 0.464 1.66e-13 1e-09 232 TrdLayer Transportation 161 131 356 -125 0.464 1.69e-13 1.02e-09 232 TrdLayer Transportation ... and so on... In some events, G4 seems to be able to recognize and amend the situation: WARNING - G4Navigator::ComputeStep() Track stuck, not moving for 10 steps in volume -TrdLayer- at point (-9.019548462,-67.04845417,311.976) direction: (0.9993687785,0.004953406355,0.03517823564). Potential geometry or navigation problem ! Trying pushing it of 9e-10 mm ... WARNING - G4Navigator::ComputeStep() Track stuck, not moving for 10 steps in volume -TrdLayer- at point (-9.019548454,-67.04845417,311.976) direction: (0.9993687787,0.004953406355,0.03517823201). Potential geometry or navigation problem ! Trying pushing it of 9e-10 mm ... ... and so on ... I also attach some output from /tracking/verbose 6 which seems to indicate a problem in the transportation process: #Step# X(mm) Y(mm) Z(mm) KinE(MeV) dE(MeV) StepLeng TrackLeng NextVolume ProcName 1082 -89.7 -63.5 -285 0.207 1.17e-10 6.93e-09 32.1 TrdModule Transportation >>DefinePhysicalStepLength (List of proposed StepLengths): ++ProposedStep(PostStep ) = 1.797693134862316e+308 : ProcName = GammaXTRadiator (No ForceCondition) ++ProposedStep(PostStep ) = 1.797693134862316e+308 : ProcName = ElectroNuclear (No ForceCondition) ++ProposedStep(PostStep ) = 66843.92633942491 : ProcName = eBrem (No ForceCondition) ++ProposedStep(PostStep ) = 43.73431611726596 : ProcName = eIoni (No ForceCondition) ++ProposedStep(PostStep ) = 1.797693134862316e+308 : ProcName = msc (Forced) ++ProposedStep(PostStep ) = 1.797693134862316e+308 : ProcName = Transportation (Forced) ++ProposedStep(AlongStep) = 1.797693134862316e+308 : ProcName = eBrem (CandidateForSelection) ++ProposedStep(AlongStep) = 559.1135940543439 : ProcName = eIoni (CandidateForSelection) ++ProposedStep(AlongStep) = 0.1951978999090939 : ProcName = msc (CandidateForSelection) ++ProposedStep(AlongStep) = 0 : ProcName = Transportation (CandidateForSelection) >>AlongStepDoIt (process by process): Process Name = Transportation ++G4Step Information Address of G4Track : 0xc7b28c8 Step Length (mm) : 0 Energy Deposit (MeV) : 0 ----------------------------------------------------------------------- StepPoint Information PreStep PostStep ----------------------------------------------------------------------- Position - x (mm) : -89.70796591921498 -89.70796591921498 Position - y (mm) : -63.48666293803226 -63.48666293803226 Position - z (mm) : -285.232 -285.232 Global Time (ns) : 4.079087373687271 4.079087373687271 Local Time (ns) : 0.1366161237314643 0.1366161237314643 Proper Time (ns) : 0.08792145067135242 0.08792145067135242 Momentum Direct - x : -0.9805329125797901 -0.9805329125797901 Momentum Direct - y : 0.1807490143955495 0.1807490143955494 Momentum Direct - z : -0.07671376110471373-0.07671376110471372 Momentum - x (MeV/c): -0.4943958688733998 -0.4943958688733998 Momentum - y (MeV/c): 0.09113571291042878 0.09113571291042877 Momentum - z (MeV/c): -0.03867995259447763-0.03867995259447762 Total Energy (MeV) : 0.717878242726697 0.717878242726697 Kinetic Energy (MeV): 0.2068791827266971 0.2068791827266971 Velocity (mm/ns) : 210.5632471109914 210.5632471109914 Volume Name : TrdModule TrdModule Safety (mm) : 0 0 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 ----------------------------------------------------------------------- !Note! Safety of PostStep is only valid after all DoIt invocations. ++G4ParticleChange Information ----------------------------------------------- G4ParticleChange Information ----------------------------------------------- # of 2ndaries : 0 ----------------------------------------------- Energy Deposit (MeV): 0 Track Status : Alive True Path Length (mm) : 0 Stepping Control : 0 Mass (GeV) : 0 Charge (eplus) : 0 Position - x (mm) : -89.7 Position - y (mm) : -63.5 Position - z (mm) : -285 Time (ns) : 4.08 Proper Time (ns) : 0.0879 Momentum Direct - x : -0.981 Momentum Direct - y : 0.181 Momentum Direct - z : -0.0767 Kinetic Energy (MeV): 0.207 Polarization - x : 0 Polarization - y : 0 Polarization - z : 0 Track Weight : 0 Touchable (pointer) : 0xce40500 ++List of secondaries generated (x,y,z,kE,t,PID): No. of secodaries = 0 ... and so on ... The following output is generated by my SteppingAction, for every 100th tiny step: /tracking/verbose 0 PROBLEM! 1100 tiny steps for Track ID 24, created by hIoni Particle: e- E= 0.2068791823444467 MeV Position: (-89.70796597055939,-63.48666292857455,-285.2320000000736) Currently in volume TrdModule PROBLEM! 1200 tiny steps for Track ID 24, created by hIoni Particle: e- E= 0.2068791822041985 MeV Position: (-89.70796601061012,-63.48666292118423,-285.2320000002578) Currently in volume TrdLayer PROBLEM! 1300 tiny steps for Track ID 24, created by hIoni Particle: e- E= 0.2068791819313116 MeV Position: (-89.70796605944828,-63.48666291218628,-285.2320000004788) Currently in volume TrdRadiator PROBLEM! 1400 tiny steps for Track ID 24, created by hIoni Particle: e- E= 0.2068791815863 MeV Position: (-89.70796611145013,-63.48666290259673,-285.2320000001471) Currently in volume TrdModule PROBLEM! 1500 tiny steps for Track ID 24, created by hIoni Particle: e- E= 0.2068791813122284 MeV Position: (-89.70796615936021,-63.48666289376921,-285.232000000331) Currently in volume TrdLayer PROBLEM! 1600 tiny steps for Track ID 24, created by hIoni Particle: e- E= 0.2068791810473755 MeV Position: (-89.70796620763744,-63.48666288485973,-285.2320000000367) Currently in volume TrdRadiator PROBLEM! 1700 tiny steps for Track ID 24, created by hIoni Particle: e- E= 0.2068791806160801 MeV Position: (-89.70796626474066,-63.48666287434693,-285.232000000257) Currently in volume TrdModule PROBLEM! 1800 tiny steps for Track ID 24, created by hIoni Particle: e- E= 0.2068791804162851 MeV Position: (-89.70796630829986,-63.48666286632119,-285.2320000004406) Currently in volume TrdLayer PROBLEM! 1900 tiny steps for Track ID 24, created by hIoni Particle: e- E= 0.2068791796872486 MeV Position: (-89.70796638370334,-63.4866628524233,-285.2320000001464) Currently in volume TrdRadiator PROBLEM! 2000 tiny steps for Track ID 24, created by hIoni Particle: e- E= 0.2068791794378897 MeV Position: (-89.70796643017182,-63.48666284385618,-285.2320000003289) Currently in volume TrdModule The interesting part is the current volume that fluctuates although the position of the particle remains virtually constant. The hierarchy in my geometry is as follows: TrdLayer | |__ TrdModule | |__TrdRadiator (among others) So, a particle should never really enter a "TrdLayer" volume explicitly because the daughter volume "TrdRadiator" in each "TrdModule" fills the upper part of the layer completely. My setup contains a homogeneous magnetic field. What also puzzles me is the fact that the minimum stepsize in the G4MagInt_Driver should prevent steps from being as small as I observe them, shouldn't it? The parameters for tracking in the magnetic field are as follows: Magnetic field: min epsilon step: 5e-05 mm Magnetic field: max epsilon step: 0.001 mm Magnetic field: delta one step: 0.01 mm Magnetic field: delta intersection: 0.001 mm Unfortunately, the G4MagInt_Driver doesn't have a Get() for the minimum stepsize, so I assume it is the default value of stepMinimum = 1.0e-2 * mm (see G4ChordFinder). Can this be ignored by the transportation process? I carefully checked the geometry for volume overlaps. Any insight would be appreciated, kind regards Henning

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