On the stability and stationarity of the Super H-mode combined with an ion transport barrier in the core

M. Knolker*, T. E. Evans, P. B. Snyder, B. Grierson, J. Hanson, Aaro Järvinen, X. Jian, J. McClenaghan, T. Osborne, C. Paz-Soldan, W. Solomon, T. Wilks

*Corresponding author for this work

Research output: Contribution to journalArticleScientificpeer-review

17 Citations (Scopus)

Abstract

The Super H-mode, a regime with high pedestal pressure and stored energy, is explored on DIII-D and combined with an ion transport barrier in the plasma core to increase performance. A significant improvement of ion temperatures and confinement is facilitated by favorable conditions such as high rotational shear and high ion pedestal temperatures. As a result of a rise in density and simultaneous decrease in rotation, the ion transport barrier disappears during the discharge evolution, leading to a transition from a very high confinement state at early times, to a reduced but still high confinement phase. Additionally, in many discharges, a global magnetohydrodynamic (MHD) event consistent with the coupling of a destabilized internal mode to an edge localized mode causes a large energy loss and leads to a reorganization of the plasma into a lower temperature, higher density state. Depending on the magnitude of the global MHD event, the plasma edge collisionality can increase significantly and shift the operational boundary from the peeling to the ballooning side, which can be understood as a drop out of the Super H-mode channel into standard H-mode. Hence, in Super H-mode discharges with ion transport barriers, both the improved pedestal height and rotational shear contribute to the high stored energy. At very low levels of rotation, the confinement factor for SH modes is still expected to exceed standard H-mode by 20%-30%. With their overall stationarity and high-performance levels, Super H-mode discharges provide an attractive regime for ITER and may enable a more compact design of future fusion power plants.

Original languageEnglish
Article number025017
JournalPlasma Physics and Controlled Fusion
Volume63
Issue number2
DOIs
Publication statusPublished - Feb 2021
MoE publication typeA1 Journal article-refereed

Funding

The authors are grateful for helpful discussions with Alessandro Bortolon, Andrea Garofalo, Craig Petty, Chris Holland and Hartmut Zohm. This research was supported by the General Atomics Postgraduate Research Participation Program administered by ORAU. This material is based upon work supported by the U.S. 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 Awards DE-FC02-04ER54698, DE-AC02-09CH11466, DESC0018030, DE-AC52-07NA27344, DE-FG02-04ER54761, DE-SC0018287. Part of the data analysis was performed using the OMFIT integrated modeling framework [74]. We gratefully acknowledge the support of the DIII-D Team for tokamak, auxiliary heating, and diagnostic systems operation.

Keywords

  • Pedestal
  • Stability
  • Super H-mode
  • Transients

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