Title: Challenges in Modeling Collisional and Turbulent Transport in Tokamak Fusion Plasmas (Video)
Abstract: One of the outstanding challenges in developing fusion as a practical energy source is improving energy confinement so that a large number of reactions take place. To do this will require reducing plasma transport by minimizing the heat fluxes out of the plasma. In the tokamak core, plasma cross-field heat and particle fluxes are dominated by two processes: neoclassical transport (due to Coulomb collisions) and turbulent transport (due to temperature and density gradient-driven microinstabilities). While neoclassical transport is generally subdominant to turbulent transport by at least one order of magnitude in the tokamak core, neoclassical dynamics is a key component in explaining enhanced edge flows, current, and confinement phenomena, in which turbulence is significantly suppressed. A comprehensive approach to integrated modeling of profile temperature and density evolution requires both of these processes. This talk describes the application of first-principles kinetic theory and simulations to understand the physical mechanisms driving plasma transport, using state-of-the-art drift-kinetic simulations to compute the collisional fluxes and gyrokinetic simulations to compute the complementary turbulent fluxes. The novel numerical algorithms necessary to overcome the computational challenges due to the high phase-space dimensionality (2 spatial and 2 velocity), self-consistent evolution of the electric and magnetic fields, and the large separation of scales between ions and electrons in velocity space (m_i/m_e~3600), will be discussed, and comparisons with tokamak experiments will be shown.