Transport analysis of high radiation and high density plasmas in the ASDEX Upgrade tokamak

Abstract

Abstract. Future fusion reactors, foreseen in the "European road map" such as DEMO, will operate under more demanding conditions compared to present devices. They will require high divertor and core radiation by impurity seeding to reduce heat loads on divertor target plates. In addition, DEMO will have to work at high core densities to reach adequate fusion performance. The performance of fusion reactors depends on three essential parameters: temperature, density and energy confinement time. The latter characterizes the loss rate due to both radiation and transport processes. The DEMO foreseen scenarios described above were not investigated so far, but are now addressed at the ASDEX Upgrade tokamak. In this work we present the transport analysis of such scenarios. Plasma with high radiation by impurity seeding: transport analysis taking into account the radiation distribution shows no change in transport during impurity seeding. The observed confinement improvement is an effect of higher pedestal temperatures which extend to the core via stiffness. A non coronal radiation model was developed and compared to the bolometric measurements in order to provide a reliable radiation profile for transport calculations. High density plasmas with pellets: the analysis of kinetic profiles reveals a transient phase at the start of the pellet fuelling due to a slower density build up compared to the temperature decrease. The low particle diffusion can explain the confinement behaviour.

Theoretical and experimental aspects of non-equilibrium plasmas in different regimes: fundamentals and selected applications

“…This situation is denoted as non-coronal equilibrium and affects the edge radiation of low-Z impurities. In this case, the radiative loss function is not only a function of the temperature but also of the residence time [41]. Equation ( 1) is valid under the following assumptions: the characteristic ionization and recombination times are longer than the times of natural radiative decay of the excited states, n e is such that the mixing of the neighbouring levels is unimportant, the electromagnetic fields do not allow forbidden lines to be emitted, etc.…”