A unified model of density limit in fusion plasmas

TL;DR

This paper presents a unified model for the density limit in fusion plasmas, linking it to radiation losses, plasma current, and input power, aligning with experimental and empirical scalings across different devices.

Contribution

It introduces a minimal cylindrical magneto-thermal equilibrium model that unifies various empirical density limit scalings in fusion devices.

Findings

Density limit scales linearly with plasma current in tokamaks and RFPs.

Auxiliary heating influences the limit, scaling with the 0.4 power of input power.

Purely externally heated configurations follow a Sudo-like power dependence.

Abstract

A limit for the edge density, ruled by radiation losses from light impurities, is established by a minimal cylindrical magneto-thermal equilibrium model. For ohmic tokamak and reversed field pinch the limit scales linearly with the plasma current, as the empirical Greenwald limit. The auxiliary heating adds a further dependence, scaling with the 0.4 power, in agreement with L-mode tokamak experiments. For a purely externally heated configuration the limit takes on a Sudo-like form, depending mainly on the input power, and is compatible with recent Stellarator scalings.