Simulation analysis of the dynamic response of burning fusion plasmas

Abstract

The global dynamics of temperature and density in a fusion plasma is investigated by numerical simulation of coupled nonlinear (reaction-diffusion) partial differential equations. The simultaneous influence on the plasma behaviour of several dynamic processes, e.g. heat conduction and particle diffusion, heat and particle pinch effects, alpha particle heating as well as thermalization of the alpha particles is considered. Particular interest is paid to the influence of extended forms of the heat conduction and particle diffusion coefficients, motivated by experimental observations. It is shown that driven periodic perturbations in the transport and/or source coefficients may result in a plasma response, which exhibits a mixture of free (natural) and forced oscillations of a burning fusion plasma. The oscillations, which are generally nonlinear, refer to an equilibrium (stationary point) which is, however, never reached in the dynamic process, of evolution due to the presence of the driven periodic oscillations. The response caused by the driven perturbations instead remains after the natural oscillations have disappeared. The long term response as well as the characteristics of the separate free oscillations contain information about the source and transport coefficients. The simulations extend and confirm recent results of analytic model calculations (valid for the central domain of the plasma) which are useful for predicting and interpreting the global dynamic behaviour of the fusion plasma [1].