Modelling of improved confinement - peaked profiles modes and H-mode

Theoretical models on improved confinement with a peaked density profile and on the H-mode are discussed. A model theory of inward pinch and peaked density profile of Ohmic discharges in tokamaks is presented. Ion anomalous viscosity in the presence of sheared toroidal rotation causes a drift across the magnetic field. The ratio of viscosity to diffusion coefficient, the Prandtl number, determines the structures of Er and the density profile in a stationary state. In viscous plasmas, peaked profiles of both density and rotation velocity are possible without central particle momentum sources. The resulting rotation of the core relative to the edge is a direction opposite to that of the plasma current. Reduction of edge neutrals can induce further density peaking. The H-mode transition model is further developed. The radial derivative of Er, Er', changes the ion loss cone loss through squeezing of the poloidal gyroradius and electron loss by affecting the microinstabilities. The charge neutrality condition predicts a cusp type catastrophe in the relationship between gradient and flux at edge. At the transition, Er' jumps to negative values and fluctuations and anomalous fluxes are reduced simultaneously. The combined model predicts that the core density profile is flattened during the H-phase. (author). 13 refs, 2 figs