Theory-based scaling laws of near and far scrape-off layer widths in single-null L-mode discharges

TL;DR

This paper derives and validates theoretical scaling laws for near and far scrape-off layer widths in L-mode tokamak discharges, using a two-fluid model and comparing with simulations and experimental data.

Contribution

It introduces analytical scaling laws for SOL widths in L-mode plasmas, validated against simulations and multi-machine experimental data.

Findings

Good agreement between theory, simulations, and experiments for near SOL widths.

Far SOL width scaling law requires more multi-machine data for validation.

The models improve understanding of transport processes in tokamak edge plasmas.

Abstract

Theory-based scaling laws of the near and far scrape-off layer (SOL) widths are analytically derived for L-mode diverted tokamak discharges by using a two-fluid model. The near SOL pressure and density decay lengths are obtained by leveraging a balance among the power source, perpendicular turbulent transport across the separatrix, and parallel losses at the vessel wall, while the far SOL pressure and density decay lengths are derived by using a model of intermittent transport mediated by filaments. The analytical estimates of the pressure decay length in the near SOL is then compared to the results of three-dimensional, flux-driven, global, two-fluid turbulence simulations of L-mode diverted tokamak plasmas, and validated against experimental measurements taken from an experimental multi-machine database of divertor heat flux profiles, showing in both cases a very good agreement. Analogously, the theoretical scaling law for the pressure decay length in the far SOL is compared to simulation results and to experimental measurements in TCV L-mode discharges, pointing out the need of a large multi-machine database for the far SOL decay lengths.