Transport parameters in magnetic field

Physics Processes, Models and Cross Sections
1

Dear experts,

I am currently working with GATE with Geant4 Version: 11.3.0, but unfortunately, I have not received a response from their mailing list, so I hope it’s okay to ask here.

I would like to investigate transport parameters relevant to magnetic fields—specifically miss distance, delta intersection, and delta one step. I’m trying to determine their default values, but they do not seem to be printed in the output.

Is there a way to output these values during runtime or simulation initialization? Alternatively, is there a source where the default values for these parameters are documented?

Any advice or suggestions would be greatly appreciated!

Thank you in advance!

Cheers,
Jing

2

Hi @JSWong19

Thank you for your post.

You may find a detailed explanation of how transportation in magnetic field works and what is the meaning of each tunable parameter in the Manual for Application Developers [1]. That is the main source of documentation of Geant4.

In addition, the topic is reviewed in the annual Advanced Course of Geant4, you may find the slides and the recording here [2].

Please let us know if something is not clear in the documentation, so we can improve it :slight_smile:

Best,
Alvaro

[1] Electromagnetic Field — Book For Application Developers 11.3 documentation
[2] Geant4 Advanced Course 2024 @ CERN (14-18 October 2024): Magnetic Field · Indico

3

Hi Alvaro,

thank you for your reply! Where can I find the default/recommended values for these transport parameters?

Cheers,
Jing

4

Hi @JSWong19,

You can find the current integration parameters by increasing the verbosity in the magnetic field configuration, as described in the Geant4 documentation.

A good approach is to start with the default values.

Then you can do the following:

  • Try more conservative settings (e.g., lower DeltaOneStep, tighter EpsilonMin/Max) to check if the results change. This may slow down the simulation but may reveal integration issues.
  • Then try more aggressive settings to see how much you can speed up the simulation without losing accuracy (taking the default or conservative setting as reference)

Make sure to check physics quantities of interest (e.g., energy deposition) rather than just visual differences.

Hope that helps!

Best,
Alvaro