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

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.

First-principles density limit scaling in tokamaks based on edge turbulent transport and implications for ITER

“…A fluid model approach is justified by the high plasma collisionality in the tokamak boundary for these conditions. At high collisionality, we expect boundary turbulence to be driven mainly by resistive interchange modes, as supported by nonlinear turbulent simulations [20][21][22][23]. The effect of core radiation is included in the power entering into the scrape-off layer (SOL), P SOL = P tot − P rad 2πR 0 S p = 2πR 0 Acore s p dA, with P tot the total heating power, P rad the core radiated power and A core the area on a poloidal plane inside the LCFS.…”

X-point and divertor filament dynamics from Gas Puff Imaging on TCV

“…3 is valid only for small fluctuations relative to the mean values of n e and T e (see also [44]). For the investigated plasmas with n e ∈ [0.3, 1] • 10 19 m −3 and T e ∈ [5,25] eV, one expects α ∈ [0.4, 0.6] and β ∈ [0. 3,4] according to [40].…”

“…These could, in particular, improve predictive capabilities of the heat flux scale lengths at the target plates that are among the most critical issues for successful operation of ITER and DEMO [2]. Disentangling the different turbulent mechanisms has recently advanced significantly [24,25] and real-size, global turbulence simulations of diverted discharges are within reach as demonstrated for MAST [26], ASDEX-U [27] and TCV [28]. Systematic simulation-experimental validation was recently performed for X-point geometries on TORPEX [29] and TCV [28].…”

Turbulent transport regimes in the tokamak boundary and operational limits

“…An order of magnitude estimate of Te is then derived by integrating Eq. ( 29), leading to 39 Te ∼ 5 4…”