Manipulating density pedestal structure to improve core-edge integration towards low collisionality

H. Q. Wang, R. J. Hong, R. Groebner, X. Jian, T. Rhodes, A. W. Leonard, X. Ma, S. Mordijck, T. Wilks, Z. Yan, M. W. Shafer, F. Scotti, D. Truong, J. Ren, F. Laggner, B. A. Grierson, T. H. Osborne, D. M. Thomas, J. G. Watkins

Research output: Contribution to journalArticlepeer-review

Abstract

DIII-D experiments have achieved promising core-edge integrated plasma scenarios which combine a high-temperature low-collisionality pedestal (pedestal top temperature Te,ped > 0.8 keV and collisionality ν*ped < 1) with a partially detached divertor by leveraging the benefits of a low-density-gradient pedestal in a closed divertor. It is found that with a closed divertor and high heating power, strong gas puffing to achieve detachment moves the peak density gradient outward with respect to the maximum gradient of electron temperature and reduces the density gradient at the pedestal region, which correlates with shallow pedestal fuelling due to the closed divertor geometry. In high-current plasmas in particular, the pedestal top density is found to change little with gas puffing while the separatrix, density increases to allow access for divertor detachment. The separation between density and temperature pedestals results in a high- ηe well above the electron-temperature-gradient 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 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 access to detached divertor conditions with low temperature and heat flux towards the 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.

Original languageEnglish
Article number126061
JournalNuclear Fusion
Volume64
Issue number12
DOIs
StatePublished - Dec 2024

Funding

This material is based upon work supported by the US Department of Energy, Office of Science, Office of Fusion Energy Sciences, using the DIII-D National Fusion Facility, a DOE Office of Science user facility, under Award(s) DE-FC02-04ER54698, DE-SC0018287,DE-SC0019352, DE-AC05-00OR22725, DE-SC0019256, DE-SC0023378, DE-SC0019302, DE-SC0014264, DE-FG02-08ER54999, DE-AC52-07NA27344, DE-NA0003525 and DE-AC04-94AL85000. We would like to thank the DIII-D operation team for the support and effort for the experimental work. DISCLAIMER: This report was prepared as an account of work sponsored by an agency of the United States Government. Neither the United States Government nor any agency thereof, nor any of their employees, makes any warranty, express or implied, or assumes any legal liability or responsibility for the accuracy, completeness, or usefulness of any information, apparatus, product, or process disclosed, or represents that its use would not infringe privately owned rights. Reference herein to any specific commercial product, process, or service by trade name, trademark, manufacturer, or otherwise, does not necessarily constitute or imply its endorsement, recommendation, or favoring by the United States Government or any agency thereof. The views and opinions of authors expressed herein do not necessarily state or reflect those of the United States Government or any agency thereof.

Keywords

  • core-edge integration
  • DIIID
  • pedestal
  • turbulence

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