2024 journal article
Manipulating density pedestal structure to improve core-edge integration towards low collisionality
NUCLEAR FUSION, 64(12).
author keywords: pedestal; core-edge integration; turbulence; DIIID
open access via doi.org (publisher)
Source: Web Of Science
Added: November 12, 2024
Abstract DIII-D experiments have achieved promising core-edge integrated scenario plasmas which combine high-temperature low-collisionality pedestal (pedestal top temperature Te,ped>0.8keV and collisionality *ped <1) with partially detached divertor by leveraging the benefits of low-density-gradient pedestal in a closed divertor. It is found that, with a closed divertor and high heating power, strong gas puffing for achieving detachment moves the peak density gradient outwardly with respect to the maximum gradient of electron temperature and reduces the density gradient at pedestal region, which correlates with shallow pedestal fuelling due to the closed divertor geometry. Particularly, in the high current plasmas, the pedestal top density is found to change little with local gas puffing, while the separatrix density increases to allow the access of divertor detachment. The separation between density and temperature pedestals results in high ηe well above the ETG stability threshold. Electron turbulence is found to be enhanced in the pedestal and correlated with high ηe resulting from the pedestal shift. The pedestal is wider than the EPED scaling. A revised empirical width scaling is derived based on the combination of EPED scaling with the ηe and highlights the important role of additional turbulence on the pedestal structure. The wide temperature pedestal facilitates the achievement of a high-temperature, low-collisionality pedestal and high global performance. Simultaneously, the outward shift of the density pedestal facilitates the access to detached divertor conditions with low temperature and heat flux towards target plate. This approach may be promising for closing the core-edge integration gap for future fusion reactors, which may have a weak-gradient density pedestal due to the highly opaque boundary plasmas.