Negative consequences of dynamo Core stochasticity
The simultaneous presence of several MHD resistive mode which are resonant in the core plasma leads to magnetic field stochasticity. This is due to the formation of several magnetic islands which are large enough to superpose.
In the stochastic regime the magnetic surfaces are destroyed, and magnetic field lines fill ergodically the plasma volume generating magnetic chaos.
A consequence of the core stochasticity is poor plasma confinement. Indeed, transport analysis has shown that the thermal conductivity (chi) and the particle diffusion coefficient (D) are very high in the core, as shown in the figure. Furthermore, the ratio of these two coefficients is almost equal to the square root of the ratio of the ion mass to the electron mass, as expected in a situation where the magnetic field stochasticity is the main drive for the transport processes.
Most of the plasma confinement in the RFX plasma takes place in the edge region (externally to the toroidal magnetic field reversal surface), where good magnetic surfaces are present. This is confirmed by the lower values of the transport coefficients in this region. Indeed, probe measurements have confirmed that the particle transport in the outer region is mainly driven by electrostatic turbulence.