title: New Paradigm for Turbulent Transport Across a Steep Gradient in Toroidal Plasmas.
abstract: First principles gyrokinetic simulation of the edge turbulent transport in toroidal plasmas finds a reverse trend in the turbulent transport coefficients under strong gradients. It is found that there exist both linear and nonlinear critical gradients for the nonmonotonicity of transport characteristics. The discontinuity of the transport flux slope around the turning gradient shows features of a second order phase transition. Under a strong gradient the most unstable modes are in nonground eigenstates with unconventional mode structures, which significantly reduces the effective correlation length and thus reverse the transport trend. Our results suggest a completely new mechanism for the low to high confinement mode transition without invoking shear flow or zonal flow.
authors.affiliation: Institute for Fusion Theory and Simulation, Department of Physics, Zhejiang University, Hangzhou 310027, People's Republic of China.
authors.forename: H S
authors.initials: HS
authors.lastname: Xie
authors.affiliation: Institute for Fusion Theory and Simulation, Department of Physics, Zhejiang University, Hangzhou 310027, People's Republic of China.
authors.forename: Y
authors.initials: Y
authors.lastname: Xiao
authors.affiliation: Department of Physics and Astronomy, University of California, Irvine, California 92697, USA.|Fusion Simulation Center, School of Physics, Peking University, Beijing 100871, China.
authors.forename: Z
authors.initials: Z
authors.lastname: Lin