Power dependence of density limit due to plasma-wall interaction in a burning plasma

TL;DR

This paper develops a model explaining the power dependence of the density limit in tokamaks, linking plasma-wall interactions to fusion performance, and extends it to predict conditions for burning plasma.

Contribution

It introduces a plasma-wall self-organization model that captures the power dependence of the density limit and applies it to burning plasma regimes.

Findings

Power dependence of density limit matches multiple tokamak data

Plasma-wall sputtering and confinement time are key factors

Model predicts conditions for entering burning plasma

Abstract

The density limit is one of the major obstacles to achieving the desired fusion performance in tokamaks. However, the underlying physics mechanism for its recently observed power dependence in experiments has not been well understood or predicted in theory. In this work, the power dependent scalings of density limit are obtained based on the plasma-wall self-organization model [D.F. Escande 2022 NF], which are able to match the power dependence of density limits in multiple tokamak devices. The key factors influencing the power dependence are found to be the plasma-wall sputtering and the particle confinement time. The effects of non-sputtered impurities and fusion products are further evaluated. This PWSO-density limit model is then extended to the burning plasma regime and used to predict the conditions for entering burning plasma.