vansig wrote: the ions are flowing along the surface of a toroid.
Not only on the surface, but when the fuel inside the plasmoid is very hot it ionizes itself to a great degree, so it is not just the surface. This is why I am thinking about the analogy with a toothpaste. When the bulk ions are compressed they are forced out of inner part of the torus. So, when the plasmoid starts to shrink, we have an overpopulations of ion and free hot electrons. They will follow the magnetic lines, but given that:
1.the outer part is already populated by the electrons of the filaments
2.the plasmoid is shriking
3.The field falls by 1/z^3 at the azial axis ( the toroid is a dipole)
The ions and those free electron ends up leaking from the plasmoid.
