It occurs within a plasma with an associated electric field, that causes convection of ions and electrons inward towards a central twisting filamentary axis.
A temperature gradient within the plasma will also cause chemical separation based on different ionization potentials.
[1] In Marklund's paper, the plasma convects radially inwards towards the center of a cylindrical flux tube.
During this convection, the different chemical constituents of the plasma, each having its specific ionization potential, enters into a progressively cooler region.
The plasma constituents will recombine and become neutral, and thus no longer under the influence of the electromagnetic forcing.