The origin of transport barriers in toroidal plasmas
  A transport barrier in a toroidal plasma is treated as the boundary region between the hot and cold phases of the plasma. These two phases possess essentially different collisional and transport properties, so the boundary region between them corresponds to the minimum values of specific resistivity and transport coefficients of the plasma. The behavior of magnetic shear in the region of a transport barrier and some other specific properties of transport barriers are the consequences of the minimum plasma resistivity in this region. The origin of sawtooth oscillations in toroidal plasmas is shown to have a similar nature. 
Fedor V.Prigara