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Forum: Fields: Magnetic and Otherwise
Re: None Mixed Electromagnetic field and ChordFinder (Francois Mauger)
Re: None Electric field and "local time goes back" issue (Francois Mauger)
Date: 24 Apr, 2015
From: John Apostolakis <John Apostolakis>

Dear Francois,

Thank you for your clear message.  

Could you try to run your program with most recent versions of Geant4 ?  There is a possibility that there was an underlying error which has already been found and fixed - but the fix was not available in Geant4 9.6 patch 1.   

It would be ideal if you can use the latest Geant4 release and patch - Geant4 10.1 patch 1. 

In case you are not able to use your program with this, can you please upgrade to 9.6 patch 4, as this contains many fixes which were identified since the creation of 9.6 patch1.  ( It is difficult for us to justify trying to find an error in patch 1, if it has already been fixed in patch 4.)

Let me provide some background about the issue.

In setups in which there is an electric field, the field propagation classes integrate time during the motion along the curved trajectory.  This is needed because the velocity changes (along with the momentum) - which does not happen in the case of a pure magnetic field.
So the code which is exercised in this case is not used in the pure B field case.  Different behaviour is expected - although an error is not.

I hope that these suggestions lead you to obtain a version which already works.  Please let us know if the issue is corrected (or not), and which version of Geant4 you have used.

In case it does not resolve the issue, we will need some more information to help us to diagnose it.  We encourage you to provide it by filing a problem report in the Geant4 problem reporting system (you can find the link to it in the Support pages on the Geant4 web site.)  This will also allow you and us to better track the progress of the issue.

Best regards, 
John Apostolakis
===================================================
John Apostolakis,  PH Department, CERN


> On 23 Apr 2015, at 10:42, Francois Mauger <mauger@lpccaen.in2p3.fr> wrote:
> 
> 
> *** Discussion title: Fields: Magnetic and Otherwise
> 
> Hi all,
> 
> I have a Geant4 setup that implements a field with both magnetic and 
> electric components.
> I can activate on demand the electric field. Basically, my program compiles
> and runs. I fire electrons of 1 MeV in STP air with a Bz magfield and Ey 
> electric field.
> However with the electric field activated I obtain random step errors 
> like the following:
> 
> <pre>
> ...
> *************************************************************
>  Geant4 version Name: geant4-09-06-patch-01    (1-February-2013)
>                       Copyright : Geant4 Collaboration
>                       Reference : NIM A 506 (2003), 250-303
>                             WWW : http://cern.ch/geant4
> *************************************************************
> ...
> [notice:virtual void mctools::g4::event_action::BeginOfEventAction(const 
> G4Event*):171] Event #1
> [notice:virtual void mctools::g4::event_action::BeginOfEventAction(const 
> G4Event*):171] Event #2
> [notice:virtual void mctools::g4::event_action::BeginOfEventAction(const 
> G4Event*):171] Event #3
> [notice:virtual void mctools::g4::event_action::BeginOfEventAction(const 
> G4Event*):171] Event #4
> [notice:virtual void mctools::g4::event_action::BeginOfEventAction(const 
> G4Event*):171] Event #5
> [notice:virtual void mctools::g4::event_action::BeginOfEventAction(const 
> G4Event*):171] Event #6
> [notice:virtual void mctools::g4::event_action::BeginOfEventAction(const 
> G4Event*):171] Event #7
>   G4ParticleChange::CheckIt    : the local time goes back  !! 
> Difference:  0.14314337090688[ns]
> e- E=0.0012850040011642 pos=0.011471222165611, -0.070632466275141, 
> -0.097956932327808 global time=0.14314337090688 local time=0 proper time=0
>   G4ParticleChange::CheckIt    : the proper time goes back  !! 
> Difference:  0.14278431258136[ns]
> e- E=0.0012850040011642 pos=0.011471222165611, -0.070632466275141, 
> -0.097956932327808 global time=0.14314337090688 local time=0 proper time=0
>       -----------------------------------------------
>         G4ParticleChange Information
>       -----------------------------------------------
>         # of 2ndaries       :                    0
>       -----------------------------------------------
>         Energy Deposit (MeV):                    0
>         Non-ionizing Energy Deposit (MeV):                    0
>         Track Status        :                Alive
>         True Path Length (mm) :               0.0313
>         Stepping Control      :                    0
>         Mass (GeV)   :                    0
>         Charge (eplus)   :                    0
>         MagneticMoment   :                    0
>                 :  =                    0*[e hbar]/[2 m]
>         Position - x (mm)   :                 11.5
>         Position - y (mm)   :                -70.6
>         Position - z (mm)   :                -97.9
>         Time (ns)           :               -0.143
>         Proper Time (ns)    :               -0.143
>         Momentum Direct - x :               -0.428
>         Momentum Direct - y :                0.721
>         Momentum Direct - z :                0.545
>         Kinetic Energy (MeV):              0.00129
>         Velocity  (/c):               0.0708
>         Polarization - x    :                    0
>         Polarization - y    :                    0
>         Polarization - z    :                    0
>         Touchable (pointer) :            0x2511f90
> 
> -------- EEEE ------- G4Exception-START -------- EEEE -------
> *** G4Exception : TRACK003
>       issued by : G4ParticleChange::CheckIt
> momentum, energy, and/or time was illegal
> *** Event Must Be Aborted ***
> -------- EEEE -------- G4Exception-END --------- EEEE -------
> 
> [notice:virtual void mctools::g4::event_action::BeginOfEventAction(const 
> G4Event*):171] Event #8
> [notice:virtual void mctools::g4::event_action::BeginOfEventAction(const 
> G4Event*):171] Event #9
> 10 events have been kept for refreshing and/or reviewing.
> Idle> exit
> ...
> </pre>
> 
> I suspect something is wrong with the parameters passed to the G4 
> field/chord/equation/stepper stuff
> but I have no hint to understand the problem.
> This problem does not occur with a pure magnetic field, only when an 
> electric component is activated.
> 
> Thanks for help.
> 
> my system: G4.9.6 on Ubuntu 14.04LTS 64bits
> 
> Fran├žois Mauger
> -- 
> 
> -------------------------------------------------------------
> Visit this GEANT4 at hypernews.slac.stanford.edu message (to reply or unsubscribe) at: 
> http://hypernews.slac.stanford.edu/HyperNews/geant4/get/emfields/225/1.html 

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1 None: Re: Electric field and "local time goes back" issue   (Francois Mauger - 25 Apr, 2015)
2 None: Re: Electric field and "local time goes back" issue   (Francois Mauger - 25 Apr, 2015)
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