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Forum: Fields: Magnetic and Otherwise
Date: 28 Jan, 2013
From: Balint Radics <Balint Radics>

Hi,

I created a simple detector structure based on one of the novice examples and incorporated
my own Field class derived from G4ElectroMagneticField and it works fine. I followed the instructions
on page:

http://geant4.web.cern.ch/geant4/UserDocumentation/UsersGuides/ForApplicationDeveloper/html/ch04s03.html

and I can see the charged particles trajectories bending in the field OK. It is actually on sourceforge in case
you want to look at it (just private code, nothing fancy):

https://sourceforge.net/p/cuspg4/code/21/tree/trunk/Ex1/src/Field.cc
https://sourceforge.net/p/cuspg4/code/21/tree/trunk/Ex1/include/Field.hh

Now, I needed to incorporate this EM field implementation into a bigger Geant4 code in which there are other
fields as well, buy they have their own local field managers created in them, and they associate the local
field managers with the relevant logical volumes only.

I also associate my field manager with separate logical volumes only. I can even see that my class's GetFieldValue() function is being called all the time but still I cannot see the particle trajectories bending!

My original code (with a single global field manager) works both under 4.9.4.p04 and  4.9.5.p02, but when
doing the same with multiple field managers it doesn't work (that I reproduced only with 4.9.4.p04 because 
we are still migrating the code to 4.9.5).

1) I suspect maybe there is some field manager ownership problem, although only local field managers are created.
Can this be a problem? How can I find out in run time which field manager is 'in action' during tracking?

2) Since I don't have any clue what the problem can be I was wondering if there is any significance that in my original code I used standard volumes (G4Box and G4Tubs), while in the other bigger code there is a lot of G4SubtractionSolids the logical volumes of which I am using to associate them with the field manager of my class.

3) Apart from GetFieldValue, is there other any other way to
-  extract what the field value is at a certain space point ?
-  debug the charged particle's evolution to find out what field value they 'see' while propagating
in space?

4) Could any of you point me to a working example code in which there are multiple field managers involved?

Thanks a lot for any hints,
Balint


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1 Feedback: Re: multiple field manager problem   (Gumplinger Peter - 28 Jan, 2013)
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