UW-CPTC 10-6 A Model Of Pedestal Structure

Predictions are developed for the structure of plasma parameter profiles of H-mode pedestals in transport quasi-equilibrium in tokamak plasmas. They are based on assuming paleoclassical radial plasma transport processes dominate throughout the pedestal. The key physical process in this model is that the electron temperature gradient in the pedestal increases to the magnitude required for paleoclassical electron heat transport to carry the large conductive radial electron heat flow from the hot core through the pedestal to the separatrix. The concomitant level of paleoclassical density transport is usually large in the pedestal compared to local fueling due to neutral recycling from outside the separatrix. Thus, in this model the pedestal density profile is usually determined not by edge fueling but rather by a combination of the separatrix density boundary condition and the pedestal density profile needed for the outward paleoclassical diffusive flux to be nearly balanced by the inward paleoclassical pinch flow. When neutral fueling effects are significant they add to the pedestal density and displace the density profile outward from the electron temperature profile. Model predictions are given for the electron density and temperature gradients, profiles and magnitudes in the pedestal. The transition into electron-temperature-gradient (ETG) driven anomalous radial electron heat transport in the core plasma determines the initial, transportlimited height of the electron pressure pedestal. Characteristics of the plasma toroidal rotation profile in the pedestal are also predicted. Model predictions are found to agree quantitatively (within about a factor of about two) with the properties of the recently studied 98889 DIII-D pedestal [J.D. Callen et al., Nucl. Fusion 50, 064004 (2010)]. Applications to other outstanding H-mode pedestal structure and evolution issues in tokamaks are also discussed. Finally, a hierarchy of experimental validation tests are suggested. ∗[email protected]; http://homepages.cae.wisc.edu/~callen