Overview of Enhanced D-alpha and Quasi Continuous Exhaust H-modes at DIII-D

Abstract

We review the Enhanced D-alpha (EDA) and Quasi-continuous Exhaust (QCE) H-modes that have recently been achieved in the DIII-D tokamak. These scenarios are free of large type-I edge-localized modes (ELMs) and achieved at high fueling compatible with divertor detachment. This makes them promising operational regimes as ELMs are a major risk for fusion pilot plants (FPPs). Access to EDA H-mode and the associated quasi-coherent mode (QCM) was observed at low heating power barely above the L-H power threshold, and increased density enabled access to EDA H-mode even at higher heating powers. The QCE H-mode was achieved at simultaneously high density and heating power, characterized also by a QCM and small ELMs with transient peaks of the total power into the divertor below about 3MW, in line with observations at ASDEX Upgrade. During the QCE H-mode, the turbulence parameter alpha_t at the separatrix is about 1 and does not separate ELMy or EDA from QCE H-modes well. Peeling ballooning stability calculations suggest that the EDA H-mode pedestal is limited by transport far away from ideal magnetohydrodynamic instability, and the QCE H-mode pedestal operates close to the ballooning branch of the stability boundary. BOUT++ simulations qualitatively reproduce the pressure collapse characteristics of the different regimes and suggest an important role of n ~ 50 resistive ballooning modes localized near the separatrix at the X-point during EDA and QCE H-modes. This work provides a foundation and guidance for further research on the access conditions and physics mechanisms of EDA and QCE H-modes necessary for the extrapolation of these regimes towards an FPP.

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BibTeX

@misc{leuthold2026overview,
  title = {{Overview of Enhanced D-alpha and Quasi Continuous Exhaust H-modes at DIII-D}},
  author = {N. Leuthold and Z. Li and M. Faitsch and A. Hyatt and C. F. B. Zimmermann and L. Gil and T. Osborne and T. Odstrcil and N. C. Logan and K. Barada and C. Chrystal and R. Gerru and S. Guizzo and R. Hood and L. Huse and S. K. Kim and C. J. Lasnier and A. O. Nelson and C. Paz-Soldan and R. Perillo and B. Victor and T. Wilks},
  howpublished = {arXiv},
  year = {2026},
  month = oct,
  doi = {10.48550/arxiv.2610.31782},
  eprint = {2610.31782},
  archivePrefix = {arXiv},
  url = {https://arxiv.org/abs/2610.31782},
}

RIS

TY  - UNPB
TI  - Overview of Enhanced D-alpha and Quasi Continuous Exhaust H-modes at DIII-D
AU  - N. Leuthold
AU  - Z. Li
AU  - M. Faitsch
AU  - A. Hyatt
AU  - C. F. B. Zimmermann
AU  - L. Gil
AU  - T. Osborne
AU  - T. Odstrcil
AU  - N. C. Logan
AU  - K. Barada
AU  - C. Chrystal
AU  - R. Gerru
AU  - S. Guizzo
AU  - R. Hood
AU  - L. Huse
AU  - S. K. Kim
AU  - C. J. Lasnier
AU  - A. O. Nelson
AU  - C. Paz-Soldan
AU  - R. Perillo
AU  - B. Victor
AU  - T. Wilks
PY  - 2026
DA  - 2026/10/22
PB  - arXiv
DO  - 10.48550/arxiv.2610.31782
UR  - https://arxiv.org/abs/2610.31782
AB  - We review the Enhanced D-alpha (EDA) and Quasi-continuous Exhaust (QCE) H-modes that have recently been achieved in the DIII-D tokamak. These scenarios are free of large type-I edge-localized modes (ELMs) and achieved at high fueling compatible with divertor detachment. This makes them promising operational regimes as ELMs are a major risk for fusion pilot plants (FPPs). Access to EDA H-mode and the associated quasi-coherent mode (QCM) was observed at low heating power barely above the L-H power threshold, and increased density enabled access to EDA H-mode even at higher heating powers. The QCE H-mode was achieved at simultaneously high density and heating power, characterized also by a QCM and small ELMs with transient peaks of the total power into the divertor below about 3MW, in line with observations at ASDEX Upgrade. During the QCE H-mode, the turbulence parameter alpha_t at the separatrix is about 1 and does not separate ELMy or EDA from QCE H-modes well. Peeling ballooning stability calculations suggest that the EDA H-mode pedestal is limited by transport far away from ideal magnetohydrodynamic instability, and the QCE H-mode pedestal operates close to the ballooning branch of the stability boundary. BOUT++ simulations qualitatively reproduce the pressure collapse characteristics of the different regimes and suggest an important role of n ~ 50 resistive ballooning modes localized near the separatrix at the X-point during EDA and QCE H-modes. This work provides a foundation and guidance for further research on the access conditions and physics mechanisms of EDA and QCE H-modes necessary for the extrapolation of these regimes towards an FPP.
ER  -

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