Minimum entropy production principle due to ohmic dissipation in tokamaks and determination of non-inductive current density profiles on JET

It is shown that a toroidal, axisymmetric, fixed-boundary plasma relaxes to a steady state where the rate of entropy production through ohmic dissipation is a minimum, the value of which depends on the boundary conditions. The plasma is assumed to evolve on a time scale slow enough for MHD equilibrium to hold at all times. Additional heating and non-inductive current drive (lower hybrid current drive, bootstrap effects) are explicitly taken into account. A code based on this variational principle has been developed to perform a fast reconstruction of radial profiles of electrical conductivity, transformer and non-inductively driven toroidal current densities in JET plasmas. Results are compared with independent computations.