Two models of turbulent pinches due to the inhomogeneity of the confining magnetic field have been proposed: the curvature and the ratchet pinches. The first is the effect of compressibility of the density due to the divergence of the ExB drift and the second reflects the influence of the magnetic field inhomogeneity on the trajectories. The relation between these models is analyzed. The average velocity for the density advected by the stochastic

A ratchet-type average velocity appears for test particles moving in a stochastic potential and a magnetic field that is space dependent. This model is developed by including particle collisions and an average velocity.