Understanding the formation of a low-pressure pedestal in the presence of a strong internal transport barrier in DIII-D high βp plasmas
As a promising scenario for fusion reactors, the high poloidal-beta ( ${\beta _{\text{P}}}$ ) scenario is characterized by a strong large radius internal transport barrier (ITB), which significantly enhances the overall confinement quality and the bootstrap current fraction for fully non-inductive o...
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| Language: | English |
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IOP Publishing
2025-01-01
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| Series: | Nuclear Fusion |
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| Online Access: | https://doi.org/10.1088/1741-4326/adab07 |
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| author | X.R. Zhang X. Jian Y.R. Zhu Y.P. Zou Z.Y. Li Y.J. Zhou L.Z. Liu S. Zheng Z.X. Wang W. Chen S.Y. Ding A.M. Garofalo V.S. Chan G.Q. Li |
| author_facet | X.R. Zhang X. Jian Y.R. Zhu Y.P. Zou Z.Y. Li Y.J. Zhou L.Z. Liu S. Zheng Z.X. Wang W. Chen S.Y. Ding A.M. Garofalo V.S. Chan G.Q. Li |
| author_sort | X.R. Zhang |
| collection | DOAJ |
| description | As a promising scenario for fusion reactors, the high poloidal-beta ( ${\beta _{\text{P}}}$ ) scenario is characterized by a strong large radius internal transport barrier (ITB), which significantly enhances the overall confinement quality and the bootstrap current fraction for fully non-inductive operation. It is frequently observed that in the presence of a strong ITB, the pedestal height is lower and is accompanied by small edge localized modes (ELMs), which further improves the compatibility of a high performance core with an edge solution. A mechanism for the formation of the low pedestal is proposed in this paper. It is found that the strong ITB creates an off-axis bootstrap current to clamp the local safety factor q , and thus the magnetic shear in the outer core/pedestal region is increased. Gyrokinetic simulations with the CGYRO code show that the higher magnetic shear brings the experimental profiles into the range where the growth rate of drift-wave instabilities and thus transport is higher, and therefore a lower pedestal gradient is expected. The combination of low pedestal and high magnetic shear further enhances the turbulent transport across the whole pedestal, consistent with power balance analysis. Such a positive feedback mechanism ultimately results in a lower pressure pedestal as observed in experiments. Under such a low pedestal, linear simulations with BOUT++ predict the growth rates of peeling–ballooning modes to be lower across the whole toroidal mode number spectra, and the nonlinear BOUT++ simulation exhibits lower saturated fluctuation intensity as well, consistent with the experimentally observed lower ELM size. |
| format | Article |
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| institution | Kabale University |
| issn | 0029-5515 |
| language | English |
| publishDate | 2025-01-01 |
| publisher | IOP Publishing |
| record_format | Article |
| series | Nuclear Fusion |
| spelling | doaj-art-e1ef789e7fae4aa4b5654380794c4c312025-01-29T15:10:35ZengIOP PublishingNuclear Fusion0029-55152025-01-0165202605910.1088/1741-4326/adab07Understanding the formation of a low-pressure pedestal in the presence of a strong internal transport barrier in DIII-D high βp plasmasX.R. Zhang0https://orcid.org/0000-0002-1943-8913X. Jian1https://orcid.org/0000-0003-3052-1694Y.R. Zhu2Y.P. Zou3https://orcid.org/0000-0003-3311-5931Z.Y. Li4https://orcid.org/0000-0003-3932-9244Y.J. Zhou5https://orcid.org/0009-0008-3251-781XL.Z. Liu6https://orcid.org/0009-0008-7934-4848S. Zheng7Z.X. Wang8W. Chen9https://orcid.org/0000-0002-9382-6295S.Y. Ding10https://orcid.org/0000-0002-1930-0439A.M. Garofalo11https://orcid.org/0000-0002-8244-2448V.S. Chan12G.Q. Li13https://orcid.org/0000-0003-0792-4348Key Laboratory of Materials Modification by Beams of the Ministry of Education, School of Physics, Dalian University of Technology , Dalian 116024, China; Southwestern Institute of Physics , Chengdu 610041, ChinaChinese Academy of Sciences, Institute of Plasma Physics , Hefei 230031, China; General Atomics , San Diego, CA 92186-5608, United States of AmericaSouthwestern Institute of Physics , Chengdu 610041, ChinaSouthwestern Institute of Physics , Chengdu 610041, ChinaGeneral Atomics , San Diego, CA 92186-5608, United States of AmericaSouthwestern Institute of Physics , Chengdu 610041, ChinaSouthwestern Institute of Physics , Chengdu 610041, ChinaKey Laboratory of Materials Modification by Beams of the Ministry of Education, School of Physics, Dalian University of Technology , Dalian 116024, ChinaKey Laboratory of Materials Modification by Beams of the Ministry of Education, School of Physics, Dalian University of Technology , Dalian 116024, ChinaSouthwestern Institute of Physics , Chengdu 610041, ChinaGeneral Atomics , San Diego, CA 92186-5608, United States of AmericaGeneral Atomics , San Diego, CA 92186-5608, United States of AmericaGeneral Atomics , San Diego, CA 92186-5608, United States of AmericaChinese Academy of Sciences, Institute of Plasma Physics , Hefei 230031, ChinaAs a promising scenario for fusion reactors, the high poloidal-beta ( ${\beta _{\text{P}}}$ ) scenario is characterized by a strong large radius internal transport barrier (ITB), which significantly enhances the overall confinement quality and the bootstrap current fraction for fully non-inductive operation. It is frequently observed that in the presence of a strong ITB, the pedestal height is lower and is accompanied by small edge localized modes (ELMs), which further improves the compatibility of a high performance core with an edge solution. A mechanism for the formation of the low pedestal is proposed in this paper. It is found that the strong ITB creates an off-axis bootstrap current to clamp the local safety factor q , and thus the magnetic shear in the outer core/pedestal region is increased. Gyrokinetic simulations with the CGYRO code show that the higher magnetic shear brings the experimental profiles into the range where the growth rate of drift-wave instabilities and thus transport is higher, and therefore a lower pedestal gradient is expected. The combination of low pedestal and high magnetic shear further enhances the turbulent transport across the whole pedestal, consistent with power balance analysis. Such a positive feedback mechanism ultimately results in a lower pressure pedestal as observed in experiments. Under such a low pedestal, linear simulations with BOUT++ predict the growth rates of peeling–ballooning modes to be lower across the whole toroidal mode number spectra, and the nonlinear BOUT++ simulation exhibits lower saturated fluctuation intensity as well, consistent with the experimentally observed lower ELM size.https://doi.org/10.1088/1741-4326/adab07high βP scenariopedestal transportELM |
| spellingShingle | X.R. Zhang X. Jian Y.R. Zhu Y.P. Zou Z.Y. Li Y.J. Zhou L.Z. Liu S. Zheng Z.X. Wang W. Chen S.Y. Ding A.M. Garofalo V.S. Chan G.Q. Li Understanding the formation of a low-pressure pedestal in the presence of a strong internal transport barrier in DIII-D high βp plasmas Nuclear Fusion high βP scenario pedestal transport ELM |
| title | Understanding the formation of a low-pressure pedestal in the presence of a strong internal transport barrier in DIII-D high βp plasmas |
| title_full | Understanding the formation of a low-pressure pedestal in the presence of a strong internal transport barrier in DIII-D high βp plasmas |
| title_fullStr | Understanding the formation of a low-pressure pedestal in the presence of a strong internal transport barrier in DIII-D high βp plasmas |
| title_full_unstemmed | Understanding the formation of a low-pressure pedestal in the presence of a strong internal transport barrier in DIII-D high βp plasmas |
| title_short | Understanding the formation of a low-pressure pedestal in the presence of a strong internal transport barrier in DIII-D high βp plasmas |
| title_sort | understanding the formation of a low pressure pedestal in the presence of a strong internal transport barrier in diii d high βp plasmas |
| topic | high βP scenario pedestal transport ELM |
| url | https://doi.org/10.1088/1741-4326/adab07 |
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