A coherent structure transport model for scrape-off layer turbulence

TL;DR

This paper develops a fast, theory-based coherent structure transport model to analyze scrape-off layer turbulence in fusion reactors, successfully reproducing empirical heat flux scalings and revealing secondary heat flux peaks influenced by blob dynamics.

Contribution

It introduces the CST model for efficient edge plasma transport analysis, integrating it with SOLPS-ITER simulations to capture turbulence effects and heat flux profiles in realistic X-point geometries.

Findings

The model reproduces the $1/B_p$ scaling of heat load width.

Secondary heat flux peaks are linked to blob density and size.

The CST model is computationally efficient for analyzing SOLPS-ITER solutions.

Abstract

Understanding the locality of high-temperature plasma energy deposition on material surfaces in fusion reactors is critical for design. Here, we utilize the Gyrokinetic ElectroMagnetic turbulence including X-points (GEMX) simulation, together with SOLPS-ITER solutions for the background equilibrium electric field including drifts, to model the heat flux at the divertor plate and characterize the heat load width using realistic X-point geometry. We use a theory-based blobby transport model called the "Coherent Structure Transport" (CST) model to include the effect of plasma transport in the edge scrape-off layer. The CST model is extremely fast and can be used to quickly analyze any SOLPS-ITER solution. SOLPS-ITER provides the steady state, or equilibrium on which we superimpose blobby turbulence characterized by blob size, amplitude and frequency. We obtain the $1/B_p$ scaling of the heat load exponential decay width $\lambda_q$, in agreement with the Eich empirical scaling and with the Goldston heuristic theory. When including blobby turbulence in combination with the SOLPS-ITER electric field, we find a secondary peak in the heat flux radial profile, outwardly displaced from the strike point radius, with a relative amplitude that increases with the initial blob density. We describe the CST model in detail and provide initial investigations of the scaling of $\lambda_q$ and the secondary heat flux peak with blob size and amplitude.