UCLA

Abstract: This paper uses data from limited HL-2A Ohmic-plasma to answer the question of how turbulent transport broadens the heat flux width. A key issue in this study is the determination of the origin of SOL turbulence. We develop the concept of the energy production ratio R_a, which compares the flux of turbulence energy across the LCFS to the net, integrated energy production in the SOL. The flux of turbulence energy (i.e., spreading) is measured directly, using Langmuir probes. Experimental data is used to evaluate R_a. Results show that usually R_a>1, indicating that SOL turbulence is energized primarily by edge turbulence spreading. The exceptions – cases where R_a<1 – are those with relatively stronger E×B shear near the LCFS. The latter inhibits both turbulence spreading and local SOL production, but has greater effects on spreading. High blob fraction in the turbulence correlates with large values of R_a. The implications for heat flux width physics are discussed.