Electron propagation in magnetic field

[joschala]

Hi Geant4 users!

I have a simulation of electrons propagating in vacuum in a magnetic field of some few Teslas. They propagate on cyclotron trajectories accordingly after being created in vacuum by my particle generator. It allows for adjustment of the polar angle wrt to the magnetic field.

My question: as soon as the polar angle (wrt the guiding mag. field) is increased to large angles (strong gyration) or if the initial kinetic energy is chosen very low, the electron trajectories just stop mid-air after some propagation. Also in a subsequent sensitive volume they are not tracked, so it is not a displaying issue.
My suspicion is a relation to overall propagation time since both lowering energy or increasing pitch angle ( = lowering the longitudinal speed) cause the trajectories to terminate in vacuum.

Does someone know about this issue or is there a implicit (or explicit) cut at some time?

I am looking forward for your ideas!

[atolosad]

Hi,

yes, there is a cut, explained in the documentation.

To limit this CPU cost, a type of tracking cut for charged particles was introduced in Geant4 release 7.0 in G4Transportation and G4CoupledTransportation. Tracks which require more than a threshold number of integration steps [maxLoopCount] (currently 1,000) during a physics/tracking step are marked as ‘looping’ and are considered candidates for being killed - i.e. they can potentially be abandoned after the current step, and have their energy deposited locally.

In the same link you may find how to tune the parameters to get what you want.

In addition, you may check the examples under extended/field.

Best,
Alvaro