Understanding Particle Movement in a Magnetic Bottle: Field vs. Field Lines

[Samson4]

Which is correct? It's almost split 50/50 when I search online. Do the particles trapped in a magnetic bottle travel around the magnetic field or around each magnetic field line? It makes more sense for them to travel around the field because the field is what changes in density not each line. Is this correct?

 

[mfb]

You cannot count field lines. The width of their spirals depends on their momentum orthogonal to the magnetic field.

 

[Cryston Waston]

Magnetic field does not work on the particle trapped in the magnetic bottle, it just changes their direction. It is the velocity of the particle itself and the force in the axial direction which causes the oscillation.