A Survey of Thermal Instabilities in Tokamak Plasmas: Theory, Comparison with Experiment, and Predictions for Future Devices

Abstract

The strong temperature dependence, over certain temperature ranges, of the radiation cooling rate of low-Z impurities, of the atomic physics cooling and particle source rates associated with recycling and fueling neutrals, of the ion-electron recombination particle loss rate, of the turbulent transport loss rate, and of the fusion alpha-particle heating rate have all been identified as “drivers” of thermal instabilities in the coupled plasma particle, momentum, and energy balances. This paper surveys the experimental observations of a number of abrupt transition phenomena in plasma operating conditions - i.e., density-limit disruptions, multifaceted asymmetric radiations from the edge (MARFEs), divertor MARFEs, detachment, in-out divertor heat flux asymmetries, H-L and L-H transitions, confinement, and pedestal deterioration - or anticipated in future reactors - i.e., power excursions - their theoretical interpretations in terms of thermal instabilities driven by the temperature dependence of various radiative and atomic physics cooling mechanisms, and a comparison of theoretical prediction with experimental observations. Also surveyed are theoretical predictions of thermal instabilities in the power balance driven by the strong positive temperature dependence of the fusion heating rate.