Question

Outside a narrow charged stream (say, a beam of ions or electrons) is the same as observing a current through a conducting wire - there is a circular magnetic field around it.

What would happen inside a charged stream (for example, inside a conducting wire or inside a solar flare)? I have a feeling that symmetry will rule that there is no magnetic field, but I am not sure.

Answer 1

The mmf due to a current is determined by the current through the surface bounded by the closed path along which the magnetic field is integrated. A closed path within a cross-section of a conductor with, say, a uniform current density, will have a non-zero mmf associated with it and thus, a non-zero magnetic field exists within the conductor.