Integration of high confinement, high poloidal beta plasma with dual radiated power and detachment controls for divertor protection and ELM suppression

• Published in: Nuclear materials and energy 2023-03, Vol.34, p.101332, Article 101332
• Main Authors: Eldon, D., Wang, H.Q., Wang, L., Ding, S., Garofalo, A.M., Gong, X.Z., McLean, A.G., Scotti, F., Watkins, J.G., Weisberg, D.
• Format: Article
• Language: English
• Subjects: Control; Core-edge integration; Detachment
• ISSN: 2352-1791; 2352-1791
• DOI: 10.1016/j.nme.2022.101332

Divertor detachment without serious core confinement quality loss in DIII-D’s high poloidal β scenario has been combined with impurity-induced ELM mitigation without disruption. Use of Ne previously granted access to a detached, non-ELMing regime that retained high confinement quality due to stimulation of Internal Transport Barrier (ITB) growth, but suffered from on-going core fuel dilution and high disruptivity. Excess Ne accumulation in the core plasma has now been avoided by feeding back core radiated power (Prad) measurements to control Ne seeding, rather than using attachment fraction (Afrac) control with Ne; this also reduces disruptivity. At the same time, N2 seeding is used in a feedback loop with Afrac measurements, which previously posed low disruption risk. In this way, the effect of Ne in the core is managed while avoiding excess seeding, and N2 acts to correct for any excess heat exhaust that might interfere with detachment. The average Ne flow rate was 38% of what was used in pure Ne Afrac control, plus average N2 flow that was 43% of pure N2Afrac control, even while meeting an even deeper detachment target. Meanwhile, a steep pressure gradient in the core plasma reduces sensitivity to impurity-induced degradation of the pedestal and reasonable confinement quality was maintained despite operational challenges that blocked formation of an ITB in these experiments. •Simultaneous feedback control of core radiated power & divertor attachment fraction.•Use of impurity mixture avoids excess neon accumulation in core plasma.•Neon reduces ELM frequency and intensity and can lead to complete ELM suppression.•Steep core pressure gradient allows high confinement at low pedestal pressure.