Plasma simulation tools
With the development of supercomputers, simulation has become the third main pillar of scientific research besides experiments and theory
In order to understand and predict fusion experiments, that is, to tame the plasma, scientists have to construct very complex physical models and run simulations on supercomputers. The development of simulation tools requires thorough understanding of the theory and computer science, and diligent comparison to experimental results.
ASCOT – race track for fast particles in fusion reactors
There are no fusion reactions without fast particles, and fusion produces more of them – both ions (alpha particles) that will keep the plasma hot, and neutrons that are responsible for carrying out the released energy for power production. The fusion alphas are individualists whose behaviour cannot be accounted for by bulk plasma simulations, but detailed understanding of their dynamics is crucial both for maintaining the fusion reactions and for protecting the reactor wall.
At Aalto University, a suite of codes dubbed ASCOT5 has been developed to address this need, and in many aspects of the problem it has been the forerunner in its field. It is currently the most comprehensive fast-ion simulation tool and, consequently, its user license has been signed by such prestigious institutes as the Max Planck institute, Germany, and MIT, USA.
Interpreting the complex physics in the edge parts of the plasma
Scientists at VTT and Aalto University have extensive experience in applying a set of numerical tools to model the behaviour of the plasma edge and its interaction with the wall materials of fusion reactors. The large variations in plasma density and temperature and a multitude of physics mechanisms involved make this a non-trivial task, and for this purpose several different codes have been used, in close collaboration with other laboratories in Europe and worldwide. The main tools for the moment include ERO/ERO2.0 (collaboration with Forschungszentrum Jülich), SOLPS-ITER (collaboration with Max-Planck-Institut für Plasmaphysik), EDGE2D, UEDGE, and DIVIMP. Recent projects include modelling erosion of plasma-facing components in diverse types of plasmas as well as migration of impurities in the edge plasma and finally deposition of material in potentially new locations. The efforts have concentrated on JET and ASDEX Upgrade, but projects have also been addressing experiments done on DIII-D in the US (General Atomics, San Diego).
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ELMFIRE: Understanding turbulent transport helps improve the economic feasibility of fusion energy
One major issue in developing a commercial fusion power plant is the degradation of plasma confinement due to turbulent transport. Turbulence is a challenging interdisciplinary problem but especially challenging is the simulation of edge turbulence in tokamaks. Since this includes open field lines and high fluctuation levels, the conventional turbulence theories are not valid anymore. To elucidate the physics behind fundamental transport processes in tokamak plasmas, the gyrokinetic full distribution particle code ELMFIRE has been developed within the Aalto Fusion and Plasma Physics group and VTT. This basic knowledge can be used to understand and optimise the economic feasibility of future tokamaks.