Abstract:
Theoretical progress in understanding tokamak plasma transport in the last half century is reviewed focusing on the role of nonlinearly self-organized structures in turbulent plasmas. Then, recent advances in enhancing confinement are discussed with an emphasis on identification of underlying physical mechanisms. Until 90’s, radially elongated streamers were recognized as a prime candidate to explain the Bohm confinement scaling which prevailed in experiments. Then, sheared ExB zonal flows were found to reduce turbulent transport toward the end of the last century. Inclusion of the zonal flow as an important component of turbulent plasmas led to a paradigm shift initiated from simulations and theory. Later, nonlocal phenomena offered a possibility of breaking the expected gyroBohm scaling in the zonal-flow-dominated plasmas. These include the turbulent spreading and the ExB staircase in which long range transport events and the ExB zonal shear layers coexist. Finally, recent findings of enhanced confinement modes with reactor-compatible features are reported with comparisons to past achievements and limitations of internal transport barrier and H-mode plasma research.
ZOOM LINK: