Scrape-off layer power fall-off length from turbulence simulations of ASDEX Upgrade L-mode

Abstract

The scrape-off layer (SOL) power fall-off length, λq, for parameters relevant to ASDEX Upgrade (AUG) L-mode discharges is examined by means of numerical simulations. The simulation data is acquired using synthetic probe data from turbulence simulations, which gives a high temporal resolution on the full density and pressure fields, required for an accurate evaluation of λq due to the strongly intermittent signals in the SOL. Electron conduction is found to dominate the parallel heat flux close to the separatrix, while ion convection dominates in the far SOL. Good agreement is found with the experimental scaling for AUG L-mode Sieglin et al (2016 Plasma Phys. Control. Fusion 58 055015), where λq is found to scale almost linearly with the safety factor, q, and to be weakly dependent on the power across the last-closed flux surface (LCFS), P. However, P depends on a wide range of parameters. In this paper we trace this dependence and the resulting fit of λq reveals a scaling proportional to the inverse square root of the electron temperature at the LCFS, , and a linear dependence on q.