Thermal instabilities in the edge transport barrier

A linear analysis of the edge transport barrier identifies localized, two-dimensional (radial-perpendicular) thermal instabilities driven by both impurity radiation and atomic (ionization/charge-exchange/elastic scattering) cooling and suppressed by conductive and convective heat transport. These instabilities are stabilized by sufficiently large values of the edge temperature gradient. Numerical calculations indicate that such instabilities would be expected for edge conditions (electron, impurity and neutral atom densities, temperatures, gradient scale lengths) typical of current tokamak experiments.