Achievement of highly radiating plasma in negative triangularity and effect of reactor-relevant seeded impurities on confinement and transport

TL;DR

This paper demonstrates that negative triangularity plasmas can achieve high radiation and confinement without ELMs by using seeded impurities, offering a promising path for reactor-relevant high-performance operation.

Contribution

It shows the first successful achievement of highly radiating negative triangularity plasmas with high core radiation at high Greenwald fractions using seeded gases, improving confinement and stability.

Findings

High core radiation at high Greenwald fractions achieved

Confinement improvement observed with impurity seeding

No ELMs present in the high-radiation regime

Abstract

The first achievement of highly radiating plasmas in negative triangularity is shown with an operational space featuring high core radiation at high Greenwald fraction obtained with the injection of reactor-relevant seeded gases. These negative triangularity (NT) shape diverted discharges reach high values of normalized plasma pressure (BetaN > 2) at high radiation fraction with no ELMs. We demonstrate that as long as the impurity level in the core is kept low to avoid excessive fuel dilution and impurity accumulation, integration of NT configuration with high radiation fraction not only is achievable but it can lead to confinement improvement with stabilization effects originating from collisionality, ExB shear and profiles changes due to impurity radiation cooling. The underlying physics mechanism is robust and holds for a variety of impurity species. The absence of the requirement to stay in H-mode translates in a higher core radiation fraction potentially allowed in NT shape effectively mitigating the power exhaust issue. The results presented here demonstrate a path to high performance, ELM free and highly radiative regime with rector-relevant seeding gases making this regime a potential new scenario for reactor operation.