Microinstability, Entropy Production and Plasma Confinement

A variational method to obtain the plasma confinement properties in magnetic fusion devices is proposed. The most probable steady state of an inhomogeneous plasma open to external sources is seeked out by using a non-equilibrium thermodynamical and statistical mechanical approach. As a thermodynamical potential to cause anomalous loss fluxes, an irreversible entropy production rate is used, which is associated with the dissipation due to low-frequency electromagnetic fluctuations in the presence of the pressure inhomogeneity. Its conditional minimum (extremum) state, with respect to the finite inhomogeneities of the plasma parameters and the distribution of the fluctuation spectrum, corresponds to the required steady state of a dissipative structure. An external source condition is included as a constraint which makes an effective change of the potential.