Fusion reactor needs to operate at very high temperatures and high enough densities of fuel to achieve its goal, produce energy. So, how can you predict the temperature and density profiles of a plasma confined in a stellarator? Well, you would need to start first by asking about the amount of heating power, (is the source of the energy) and the ionisation of neutral atoms (the sources of plasma particles). Then, obviously, you would need to work out the losses caused by the various transport channels (neoclassical and turbulent) with high fidelity, yet fast enough, numerical codes. Why fast? –you might ask. Both sources and fluxes depend on the plasma profiles, so you will need to repeatedly compute transport fluxes and update the profiles until a local balance is achieved — that is, when the amount of energy and particles deposited within a given plasma radius matches the amount transported across it. Considering that all this takes the integration of several models and sophisticated codes needing high-performance computing, it sounds like a daunting task…
This is exactly what has been accomplished recently in the framework of Don A. Fernando’s PhD thesis. Don has put together the simulation codes, models and know-how from the Max-Planck Institut für Plasmaphysik (MPG, Germany), the Laboratorio Nacional de Fusión (CIEMAT, Spain) and overseas collaborators to try to “postdict” plasma profiles measured in the Wendelstein 7-X stellarator in various plasma scenarios. The result? With a realistic choice of the edge plasma parameters, the predicted temperature and density profiles bear a strong resemblance to the measurements! This is an impressive achievement, considering that the prediction was made not with a single model, but through the combined use of several complex codes. And this is great news in the quest for a stellarator fusion reactor –the validation of predictive tools will allow us to design magnetic configurations that are capable of confining reactor-grade plasmas.
This achievement is a manifestation of the strength of the 3D plasma turbulence simulation community in Europe, that, in recent years, has lead this and various other important developments in this cutting-edge scientific field of research.
The figures illustrate the degree of agreement between the transport simulations (GENE) and the experimental electron and ion temperature profiles (Data) and electron density profile. A low density wave-heated (ECRH) scenario and a high density neutral-beam-heated (NBI) scenario are shown.
