Reduced Physics Model of the Tokamak Scrape-off-Layer for Pulse Design

TL;DR

This paper introduces a simplified, analytic model of the tokamak scrape-off-layer (SOL) that enables efficient, self-consistent simulation of plasma edge dynamics for pulse design, validated against experimental measurements.

Contribution

The paper presents the SOL Box Model, a novel reduced physics model that calculates plasma parameters in the SOL based on core fluxes, facilitating faster, integrated simulations.

Findings

The model accurately reproduces measured plasma temperature and density profiles.

Coupling with TRANSP improves the predictive capability for tokamak edge behavior.

The approach enables practical, real-time pulse design simulations.

Abstract

The dynamic interplay between the core and the edge plasma has important consequences in the confinement and heating of fusion plasma. The transport of the Scrape-Off-Layer (SOL) plasma imposes boundary conditions on the core plasma, and neutral transport through the SOL influences the core plasma sourcing. In order to better study these effects in a self-consistent, time-dependent fashion with reasonable turn-around time, a reduced model is needed. In this paper we introduce the SOL Box Model, a reduced SOL model that calculates the plasma temperature and density in the SOL given the core-to-edge particle and power fluxes and recycling coefficients. The analytic nature of the Box Model allows one to readily incorporate SOL physics in time-dependent transport solvers for pulse design applications in the control room. Here we demonstrate such a coupling with the core transport solver TRANSP and compare the results with density and temperature measurements, obtained through Thomson scattering and Langmuir probes, of an NSTX discharge. Implications for future interpretive and predictive simulations are discussed.