Magnetic confinement fusion reactors, such as tokamaks, rely on generating fusion power by confining the burning plasma effectively inside the device. Plasma turbulence and associated heat and particle transport out of the plasma, however, degrade the confinement in such devices, thus limiting their performance. Therefore, understanding and controlling of turbulence are of great importance for improving the economics of fusion reactors. The plasma turbulence in tokamaks is studied both experimentally and computationally. The role of computational studies is to elucidate the underlying physical mechanisms for turbulent transport and, eventually, predict and manipulate plasma confinement for future reactors. This modeling effort is increasingly based on numerical tools that solve gyrokinetic Fokker-Planck–Maxwell equations in the plasma. ELMFIRE is one of these gyrokinetic tools designed for first-principles transport simulations. In this thesis, the recent code development work to improve ELMFIRE’s numerical and physical accuracy is presented. The numerical accuracy is improved by a new integration method for the parallel nonlinearity that significantly enhances the energy conservation in the simulation. The physical accuracy, in turn, is increased by a new computational grid that allows a non-uniform resolution. In addition, the simulation domain is extended to cover the entire tokamak plasma volume from the plasma center to the material boundary of a radial wall and poloidal limiter plates. The physical accuracy of ELMFIRE simulations is investigated by testing the code’s ability to reproduce a FT-2 tokamak plasma. A direct comparison of the simulation results and FT-2 data shows that the experimental steady-state profiles are not obtained numerically. In addition to this, the ELMFIRE capability to simulate scrape-off layer plasmas is examined in a toroidal limiter-like configuration. The results of this study show a formation of sheath potential and plasma flows as well as a modification of density and temperature profiles in the scrape-off layer. A numerical plasma perturbation, induced by a large radial E x B flow at the limiter-plasma boundary, is also observed in the scrape-off layer. Finally, grid resolution and boundary conditions are shown to have a significant impact on transport levels.
|Translated title of the contribution||Global Gyrokinetic Particle Simulations of Circular Limiter Tokamak Plasmas|
|Publication status||Published - 2017|
|MoE publication type||G5 Doctoral dissertation (article)|
- nuclear fusion
- computer simulation
- turbulent plasma transport