Characterization of the ELM-free negative triangularity edge on DIII-D

A. O. Nelson; L. Schmitz; T. Cote; J. F. Parisi; S. Stewart; C. Paz-Soldan; K. E. Thome; M. E. Austin; F. Scotti; J. L. Barr; A. Hyatt; N. Leuthold; A. Marinoni; T. Neiser; T. Osborne; N. Richner; A. S. Welander; W. P. Wehner; R. Wilcox; T. M. Wilks; J. Yang

doi:10.1088/1361-6587/ad6a83

Characterization of the ELM-free negative triangularity edge on DIII-D

A. O. Nelson, L. Schmitz, T. Cote, J. F. Parisi, S. Stewart, C. Paz-Soldan, K. E. Thome, M. E. Austin, F. Scotti, J. L. Barr, A. Hyatt, N. Leuthold, A. Marinoni, T. Neiser, T. Osborne, N. Richner, A. S. Welander, W. P. Wehner, R. Wilcox, T. M. WilksJ. Yang

Advanced Tokamak Physics

Research output: Contribution to journal › Article › peer-review

3 Scopus citations

Abstract

Tokamak plasmas with strong negative triangularity (NT) shaping typically exhibit fundamentally different edge behavior than conventional L-mode or H-mode plasmas. On DIII-D, every plasma with sufficiently negative triangularity (δ < δ_crit ≃ −0.12) is found to be inherently free of edge localized modes (ELMs), even at injected powers well above the predicted L-H power threshold. It is also possible to access an ELM-free state at weaker average triangularities, provided that at least one of the two x-points is still sufficiently negative. Access to the ELM-free NT scenario is found to coincide with the closure of the second stability region for infinite-n ballooning modes, suggesting that ballooning stability may play a role in limiting the accessible pressure gradient in NT plasmas. Despite this, NT plasmas are able to support small pedestals and are typically characterized by an enhancement of edge pressure gradients beyond those found in traditional L-mode plasmas. Furthermore, the pressure gradient inside of this small pedestal is unusually steep, allowing access to high core performance that is competitive with other ELM-free regimes previously achieved on DIII-D. Since ELM-free operation in NT is linked directly to the magnetic geometry, NT fusion pilot plants are predicted to maintain advantageous edge conditions even in burning plasma regimes, potentially eliminating reactor core-integration issues caused by ELMs.

Original language	English
Article number	105014
Journal	Plasma Physics and Controlled Fusion
Volume	66
Issue number	10
DOIs	https://doi.org/10.1088/1361-6587/ad6a83
State	Published - Oct 1 2024

Funding

The authors would like to particularly thank the large set of scientists that made the DIII-D NT campaign possible, as indicated in the author list of []. Some calculations performed in this study were completed through the OMFIT framework [], and the generated data are available upon request. 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-SC0022270, DE-SC0022272, DE-SC0020287, DE-FC02-04ER54698, DE-AC02-09CH11466, DE-FG02-08ER54999, DE-FG02-97ER54415, DE-AC52-07NA27344, DE-AC05-00OR22725 and DE-SC0014264.

Funders	Funder number
U.S. Department of Energy
Fusion Energy Sciences
Office of Science	DE-AC05-00OR22725, DE-SC0020287, DE-FG02-08ER54999, DE-SC0022272, DE-FC02-04ER54698, DE-AC02-09CH11466, DE-SC0022270, DE-AC52-07NA27344, DE-SC0014264, DE-FG02-97ER54415
Office of Science

Keywords

Tokamak
negative triangularity
pedestal

UN SDGs

This output contributes to the following UN Sustainable Development Goals (SDGs)

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Cite this

Nelson, A. O., Schmitz, L., Cote, T., Parisi, J. F., Stewart, S., Paz-Soldan, C., Thome, K. E., Austin, M. E., Scotti, F., Barr, J. L., Hyatt, A., Leuthold, N., Marinoni, A., Neiser, T., Osborne, T., Richner, N., Welander, A. S., Wehner, W. P., Wilcox, R., ... Yang, J. (2024). Characterization of the ELM-free negative triangularity edge on DIII-D. Plasma Physics and Controlled Fusion, 66(10), Article 105014. https://doi.org/10.1088/1361-6587/ad6a83

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title = "Characterization of the ELM-free negative triangularity edge on DIII-D",

abstract = "Tokamak plasmas with strong negative triangularity (NT) shaping typically exhibit fundamentally different edge behavior than conventional L-mode or H-mode plasmas. On DIII-D, every plasma with sufficiently negative triangularity (δ < δcrit ≃ −0.12) is found to be inherently free of edge localized modes (ELMs), even at injected powers well above the predicted L-H power threshold. It is also possible to access an ELM-free state at weaker average triangularities, provided that at least one of the two x-points is still sufficiently negative. Access to the ELM-free NT scenario is found to coincide with the closure of the second stability region for infinite-n ballooning modes, suggesting that ballooning stability may play a role in limiting the accessible pressure gradient in NT plasmas. Despite this, NT plasmas are able to support small pedestals and are typically characterized by an enhancement of edge pressure gradients beyond those found in traditional L-mode plasmas. Furthermore, the pressure gradient inside of this small pedestal is unusually steep, allowing access to high core performance that is competitive with other ELM-free regimes previously achieved on DIII-D. Since ELM-free operation in NT is linked directly to the magnetic geometry, NT fusion pilot plants are predicted to maintain advantageous edge conditions even in burning plasma regimes, potentially eliminating reactor core-integration issues caused by ELMs.",

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author = "Nelson, {A. O.} and L. Schmitz and T. Cote and Parisi, {J. F.} and S. Stewart and C. Paz-Soldan and Thome, {K. E.} and Austin, {M. E.} and F. Scotti and Barr, {J. L.} and A. Hyatt and N. Leuthold and A. Marinoni and T. Neiser and T. Osborne and N. Richner and Welander, {A. S.} and Wehner, {W. P.} and R. Wilcox and Wilks, {T. M.} and J. Yang",

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Nelson, AO, Schmitz, L, Cote, T, Parisi, JF, Stewart, S, Paz-Soldan, C, Thome, KE, Austin, ME, Scotti, F, Barr, JL, Hyatt, A, Leuthold, N, Marinoni, A, Neiser, T, Osborne, T, Richner, N, Welander, AS, Wehner, WP, Wilcox, R, Wilks, TM & Yang, J 2024, 'Characterization of the ELM-free negative triangularity edge on DIII-D', Plasma Physics and Controlled Fusion, vol. 66, no. 10, 105014. https://doi.org/10.1088/1361-6587/ad6a83

TY - JOUR

T1 - Characterization of the ELM-free negative triangularity edge on DIII-D

AU - Nelson, A. O.

AU - Schmitz, L.

AU - Cote, T.

AU - Parisi, J. F.

AU - Stewart, S.

AU - Paz-Soldan, C.

AU - Thome, K. E.

AU - Austin, M. E.

AU - Scotti, F.

AU - Barr, J. L.

AU - Hyatt, A.

AU - Leuthold, N.

AU - Marinoni, A.

AU - Neiser, T.

AU - Osborne, T.

AU - Richner, N.

AU - Welander, A. S.

AU - Wehner, W. P.

AU - Wilcox, R.

AU - Wilks, T. M.

AU - Yang, J.

PY - 2024/10/1

Y1 - 2024/10/1

N2 - Tokamak plasmas with strong negative triangularity (NT) shaping typically exhibit fundamentally different edge behavior than conventional L-mode or H-mode plasmas. On DIII-D, every plasma with sufficiently negative triangularity (δ < δcrit ≃ −0.12) is found to be inherently free of edge localized modes (ELMs), even at injected powers well above the predicted L-H power threshold. It is also possible to access an ELM-free state at weaker average triangularities, provided that at least one of the two x-points is still sufficiently negative. Access to the ELM-free NT scenario is found to coincide with the closure of the second stability region for infinite-n ballooning modes, suggesting that ballooning stability may play a role in limiting the accessible pressure gradient in NT plasmas. Despite this, NT plasmas are able to support small pedestals and are typically characterized by an enhancement of edge pressure gradients beyond those found in traditional L-mode plasmas. Furthermore, the pressure gradient inside of this small pedestal is unusually steep, allowing access to high core performance that is competitive with other ELM-free regimes previously achieved on DIII-D. Since ELM-free operation in NT is linked directly to the magnetic geometry, NT fusion pilot plants are predicted to maintain advantageous edge conditions even in burning plasma regimes, potentially eliminating reactor core-integration issues caused by ELMs.

AB - Tokamak plasmas with strong negative triangularity (NT) shaping typically exhibit fundamentally different edge behavior than conventional L-mode or H-mode plasmas. On DIII-D, every plasma with sufficiently negative triangularity (δ < δcrit ≃ −0.12) is found to be inherently free of edge localized modes (ELMs), even at injected powers well above the predicted L-H power threshold. It is also possible to access an ELM-free state at weaker average triangularities, provided that at least one of the two x-points is still sufficiently negative. Access to the ELM-free NT scenario is found to coincide with the closure of the second stability region for infinite-n ballooning modes, suggesting that ballooning stability may play a role in limiting the accessible pressure gradient in NT plasmas. Despite this, NT plasmas are able to support small pedestals and are typically characterized by an enhancement of edge pressure gradients beyond those found in traditional L-mode plasmas. Furthermore, the pressure gradient inside of this small pedestal is unusually steep, allowing access to high core performance that is competitive with other ELM-free regimes previously achieved on DIII-D. Since ELM-free operation in NT is linked directly to the magnetic geometry, NT fusion pilot plants are predicted to maintain advantageous edge conditions even in burning plasma regimes, potentially eliminating reactor core-integration issues caused by ELMs.

KW - Tokamak

KW - negative triangularity

KW - pedestal

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DO - 10.1088/1361-6587/ad6a83

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JF - Plasma Physics and Controlled Fusion

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M1 - 105014

ER -

Characterization of the ELM-free negative triangularity edge on DIII-D

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