Experimental identification of I-mode characteristics at the edge of FIRE mode in KSTAR
The edge region of the recently discovered fast ion-regulated enhancement mode (FIRE mode) (Han and Park et al 2022 Nature 609 269–275), which primarily operates in the unfavorable ion $\nabla B$ drift configuration, is investigated in detail for the first time. An ion temperature pedestal is identi...
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| Format: | Article |
| 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/adacfc |
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| author | Chweeho Heo SangJin Park GyungJin Choi Jaewook Kim Eun-jin Kim YoungMu Jeon Minjun J. Choi Hyunsun Han Choongki Sung TaikSoo Hahm Yong-Su Na |
| author_facet | Chweeho Heo SangJin Park GyungJin Choi Jaewook Kim Eun-jin Kim YoungMu Jeon Minjun J. Choi Hyunsun Han Choongki Sung TaikSoo Hahm Yong-Su Na |
| author_sort | Chweeho Heo |
| collection | DOAJ |
| description | The edge region of the recently discovered fast ion-regulated enhancement mode (FIRE mode) (Han and Park et al 2022 Nature 609 269–275), which primarily operates in the unfavorable ion $\nabla B$ drift configuration, is investigated in detail for the first time. An ion temperature pedestal is identified, while the edge electron density profile remains at low-confinement mode (L-mode) level, displaying characteristics of the edge profiles in improved energy confinement mode (I-mode). The weakly coherent mode (WCM) is observed at around 50 kHz in the spectrum of edge electron density fluctuations measured by beam emission spectroscopy. The weakly coherent feature becomes more pronounced as the amplitude of intermediate-frequency fluctuations (approximately 10–30 kHz) decreases, coinciding with a rise in the height of the temperature pedestal. The WCM propagates in the ion diamagnetic drift direction in the laboratory frame, but its propagation direction in the E × B flow frame has yet to be determined. Nonlinear phase coupling between the low-frequency density fluctuation components and the WCMs is identified, indicating the presence of zonal density. This coupling typically occurs as the H-mode transition approaches, and its potential link to a regulatory process is discussed. When the coupling manifests, intermittent bursts are observed concurrently, not just at the radial location where the WCM amplitude peaks, but throughout the edge region. No other coherent oscillations with finite frequency have been detected thus far. |
| format | Article |
| id | doaj-art-468a682edd2d4351afe83ba8e9e673b4 |
| institution | Kabale University |
| issn | 0029-5515 |
| language | English |
| publishDate | 2025-01-01 |
| publisher | IOP Publishing |
| record_format | Article |
| series | Nuclear Fusion |
| spelling | doaj-art-468a682edd2d4351afe83ba8e9e673b42025-02-07T09:04:00ZengIOP PublishingNuclear Fusion0029-55152025-01-0165303600310.1088/1741-4326/adacfcExperimental identification of I-mode characteristics at the edge of FIRE mode in KSTARChweeho Heo0https://orcid.org/0009-0004-0198-3958SangJin Park1https://orcid.org/0000-0002-4453-0439GyungJin Choi2https://orcid.org/0000-0003-0044-1650Jaewook Kim3https://orcid.org/0000-0003-0047-5498Eun-jin Kim4https://orcid.org/0000-0001-5607-6635YoungMu Jeon5https://orcid.org/0000-0002-7374-3759Minjun J. Choi6https://orcid.org/0000-0002-2825-6484Hyunsun Han7https://orcid.org/0000-0001-6506-9824Choongki Sung8https://orcid.org/0000-0002-8122-0018TaikSoo Hahm9https://orcid.org/0000-0001-7015-0547Yong-Su Na10https://orcid.org/0000-0001-7270-3846Department of Nuclear Engineering, Seoul National University , Seoul, Korea, Republic OfDepartment of Nuclear Engineering, Seoul National University , Seoul, Korea, Republic OfDepartment of Nuclear Engineering, Seoul National University , Seoul, Korea, Republic OfKorea Institute of Fusion Energy , Daejeon, Korea, Republic OfDepartment of Nuclear Engineering, Seoul National University , Seoul, Korea, Republic Of; Research Centre for Fluid and Complex Systems, Coventry University , Coventry, United Kingdom of Great Britain and Northern IrelandKorea Institute of Fusion Energy , Daejeon, Korea, Republic OfKorea Institute of Fusion Energy , Daejeon, Korea, Republic OfKorea Institute of Fusion Energy , Daejeon, Korea, Republic OfDepartment of Nuclear and Quantum Engineering, Korea Advanced Institute of Science and Technology , Daejeon, Korea, Republic OfDepartment of Nuclear Engineering, Seoul National University , Seoul, Korea, Republic OfDepartment of Nuclear Engineering, Seoul National University , Seoul, Korea, Republic OfThe edge region of the recently discovered fast ion-regulated enhancement mode (FIRE mode) (Han and Park et al 2022 Nature 609 269–275), which primarily operates in the unfavorable ion $\nabla B$ drift configuration, is investigated in detail for the first time. An ion temperature pedestal is identified, while the edge electron density profile remains at low-confinement mode (L-mode) level, displaying characteristics of the edge profiles in improved energy confinement mode (I-mode). The weakly coherent mode (WCM) is observed at around 50 kHz in the spectrum of edge electron density fluctuations measured by beam emission spectroscopy. The weakly coherent feature becomes more pronounced as the amplitude of intermediate-frequency fluctuations (approximately 10–30 kHz) decreases, coinciding with a rise in the height of the temperature pedestal. The WCM propagates in the ion diamagnetic drift direction in the laboratory frame, but its propagation direction in the E × B flow frame has yet to be determined. Nonlinear phase coupling between the low-frequency density fluctuation components and the WCMs is identified, indicating the presence of zonal density. This coupling typically occurs as the H-mode transition approaches, and its potential link to a regulatory process is discussed. When the coupling manifests, intermittent bursts are observed concurrently, not just at the radial location where the WCM amplitude peaks, but throughout the edge region. No other coherent oscillations with finite frequency have been detected thus far.https://doi.org/10.1088/1741-4326/adacfcI-modeFIRE modeweakly coherent modebicoherenceintermittency |
| spellingShingle | Chweeho Heo SangJin Park GyungJin Choi Jaewook Kim Eun-jin Kim YoungMu Jeon Minjun J. Choi Hyunsun Han Choongki Sung TaikSoo Hahm Yong-Su Na Experimental identification of I-mode characteristics at the edge of FIRE mode in KSTAR Nuclear Fusion I-mode FIRE mode weakly coherent mode bicoherence intermittency |
| title | Experimental identification of I-mode characteristics at the edge of FIRE mode in KSTAR |
| title_full | Experimental identification of I-mode characteristics at the edge of FIRE mode in KSTAR |
| title_fullStr | Experimental identification of I-mode characteristics at the edge of FIRE mode in KSTAR |
| title_full_unstemmed | Experimental identification of I-mode characteristics at the edge of FIRE mode in KSTAR |
| title_short | Experimental identification of I-mode characteristics at the edge of FIRE mode in KSTAR |
| title_sort | experimental identification of i mode characteristics at the edge of fire mode in kstar |
| topic | I-mode FIRE mode weakly coherent mode bicoherence intermittency |
| url | https://doi.org/10.1088/1741-4326/adacfc |
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