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Wang H, Todo Y, Ido T, Suzuki Y. Chirping and Sudden Excitation of Energetic-Particle-Driven Geodesic Acoustic Modes in a Large Helical Device Experiment. PHYSICAL REVIEW LETTERS 2018; 120:175001. [PMID: 29756817 DOI: 10.1103/physrevlett.120.175001] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/20/2017] [Revised: 01/24/2018] [Indexed: 06/08/2023]
Abstract
Energetic-particle-driven geodesic acoustic modes (EGAMs) observed in a Large Helical Device experiment are investigated using a hybrid simulation code for energetic particles interacting with a magnetohydrodynamic (MHD) fluid. The frequency chirping of the primary mode and the sudden excitation of the half-frequency secondary mode are reproduced for the first time with the hybrid simulation using the realistic physical condition and the three-dimensional equilibrium. Both EGAMs have global spatial profiles which are consistent with the experimental measurements. For the secondary mode, the bulk pressure perturbation and the energetic particle pressure perturbation cancel each other out, and thus the frequency is lower than the primary mode. It is found that the excitation of the secondary mode does not depend on the nonlinear MHD coupling. The secondary mode is excited by energetic particles that satisfy the linear and nonlinear resonance conditions, respectively, for the primary and secondary modes.
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Affiliation(s)
- Hao Wang
- National Institute for Fusion Science, National Institutes of Natural Sciences, Toki 509-5292, Japan
| | - Yasushi Todo
- National Institute for Fusion Science, National Institutes of Natural Sciences, Toki 509-5292, Japan
- SOKENDAI (The Graduate University for Advanced Studies), Toki 509-5292, Japan
| | - Takeshi Ido
- National Institute for Fusion Science, National Institutes of Natural Sciences, Toki 509-5292, Japan
| | - Yasuhiro Suzuki
- National Institute for Fusion Science, National Institutes of Natural Sciences, Toki 509-5292, Japan
- SOKENDAI (The Graduate University for Advanced Studies), Toki 509-5292, Japan
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Enhancement and suppression of turbulence by energetic-particle-driven geodesic acoustic modes. Sci Rep 2017; 7:16767. [PMID: 29196677 PMCID: PMC5711864 DOI: 10.1038/s41598-017-17011-y] [Citation(s) in RCA: 19] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/17/2017] [Accepted: 11/20/2017] [Indexed: 11/24/2022] Open
Abstract
We propose a novel mechanism of enhancement of turbulence by energetic-particle-driven geodesic acoustic modes (EGAMs). The dynamics of drift-wave-type turbulence in the phase space is investigated by wave-kinetic equation. Spatially inhomogeneous turbulence in the presence of a transport barrier is considered. We discovered that trapping of turbulence clumps by the EGAMs is the key parameter that determines either suppress or enhance turbulence. In regions where turbulence is unstable, EGAM suppresses the turbulence. In contrast, in the stable region, EGAM traps clumps of turbulence and carries them across the transport barrier, so that the turbulence can be enhanced. The turbulence trapped by EGAMs can propagate independent of the gradients of density and temperature, which leads to non-Fickian transport. Hence, there appear a new global characteristic velocity, the phase velocity of GAMs, for turbulence dynamics, in addition to the local group velocity and that of the turbulence spreading. With these effect, EGAMs can deteriorate transport barriers and affect turbulence substantially. This manuscript provides a basis to consider whether a coherent wave breaks or strengthen transport barriers.
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Qu ZS, Hole MJ, Fitzgerald M. Energetic Geodesic Acoustic Modes Associated with Two-Stream-like Instabilities in Tokamak Plasmas. PHYSICAL REVIEW LETTERS 2016; 116:095004. [PMID: 26991183 DOI: 10.1103/physrevlett.116.095004] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/26/2015] [Indexed: 06/05/2023]
Abstract
An unstable branch of the energetic geodesic acoustic mode (EGAM) is found using fluid theory with fast ions characterized by their narrow width in energy distribution and collective transit along field lines. This mode, with a frequency much lower than the thermal GAM frequency ω_{GAM}, is now confirmed as a new type of unstable EGAM: a reactive instability similar to the two-stream instability. The mode can have a very small fast ion density threshold when the fast ion transit frequency is smaller than ω_{GAM}, consistent with the onset of the mode right after the turn-on of the beam in DIII-D experiments. The transition of this reactive EGAM to the velocity gradient driven EGAM is also discussed.
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Affiliation(s)
- Z S Qu
- Research School of Physics and Engineering, The Australian National University, Canberra, Australian Capital Territory 2601, Australia
| | - M J Hole
- Research School of Physics and Engineering, The Australian National University, Canberra, Australian Capital Territory 2601, Australia
| | - M Fitzgerald
- CCFE Fusion Association, Culham Science Centre, Abingdon, Oxon OX14 3DB, United Kingdom
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Ido T, Itoh K, Osakabe M, Lesur M, Shimizu A, Ogawa K, Toi K, Nishiura M, Kato S, Sasaki M, Ida K, Inagaki S, Itoh SI. Strong Destabilization of Stable Modes with a Half-Frequency Associated with Chirping Geodesic Acoustic Modes in the Large Helical Device. PHYSICAL REVIEW LETTERS 2016; 116:015002. [PMID: 26799023 DOI: 10.1103/physrevlett.116.015002] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/13/2015] [Indexed: 06/05/2023]
Abstract
Abrupt and strong excitation of a mode has been observed when the frequency of a chirping energetic-particle driven geodesic acoustic mode (EGAM) reaches twice the geodesic acoustic mode (GAM) frequency. The frequency of the secondary mode is the GAM frequency, which is a half-frequency of the primary EGAM. Based on the analysis of spatial structures, the secondary mode is identified as a GAM. The phase relation between the secondary mode and the primary EGAM is locked, and the evolution of the growth rate of the secondary mode indicates nonlinear excitation. The results suggest that the primary mode (EGAM) contributes to nonlinear destabilization of a subcritical mode.
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Affiliation(s)
- T Ido
- National Institute for Fusion Science, 322-6 Oroshi, Toki, Gifu 509-5292, Japan
| | - K Itoh
- National Institute for Fusion Science, 322-6 Oroshi, Toki, Gifu 509-5292, Japan
| | - M Osakabe
- National Institute for Fusion Science, 322-6 Oroshi, Toki, Gifu 509-5292, Japan
- SOKENDAI (The Graduate University for Advanced Study), 322-6 Oroshi, Toki, Gifu 509-5292, Japan
| | - M Lesur
- Research Institute for Applied Mechanics, Kyushu University, 6-1 Kasuga-koen, Kasuga, Fukuoka 816-8580, Japan
| | - A Shimizu
- National Institute for Fusion Science, 322-6 Oroshi, Toki, Gifu 509-5292, Japan
| | - K Ogawa
- National Institute for Fusion Science, 322-6 Oroshi, Toki, Gifu 509-5292, Japan
- SOKENDAI (The Graduate University for Advanced Study), 322-6 Oroshi, Toki, Gifu 509-5292, Japan
| | - K Toi
- National Institute for Fusion Science, 322-6 Oroshi, Toki, Gifu 509-5292, Japan
| | - M Nishiura
- Graduate School of Frontier Sciences, University of Tokyo, 5-1-5 Kashiwanohara, Kashiwa, Chiba 277-8561, Japan
| | - S Kato
- National Institute for Fusion Science, 322-6 Oroshi, Toki, Gifu 509-5292, Japan
| | - M Sasaki
- Research Institute for Applied Mechanics, Kyushu University, 6-1 Kasuga-koen, Kasuga, Fukuoka 816-8580, Japan
| | - K Ida
- National Institute for Fusion Science, 322-6 Oroshi, Toki, Gifu 509-5292, Japan
- SOKENDAI (The Graduate University for Advanced Study), 322-6 Oroshi, Toki, Gifu 509-5292, Japan
| | - S Inagaki
- Research Institute for Applied Mechanics, Kyushu University, 6-1 Kasuga-koen, Kasuga, Fukuoka 816-8580, Japan
| | - S-I Itoh
- Research Institute for Applied Mechanics, Kyushu University, 6-1 Kasuga-koen, Kasuga, Fukuoka 816-8580, Japan
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Bovet A, Fasoli A, Furno I. Time-Resolved Measurements of Suprathermal Ion Transport Induced by Intermittent Plasma Blob Filaments. PHYSICAL REVIEW LETTERS 2014; 113:225001. [PMID: 25494075 DOI: 10.1103/physrevlett.113.225001] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/26/2014] [Indexed: 06/04/2023]
Abstract
Suprathermal ion turbulent transport in magnetized plasmas is generally nondiffusive, ranging from subdiffusive to superdiffusive depending on the interplay of the turbulent structures and the suprathermal ion orbits. Here, we present time-resolved measurements of the cross-field suprathermal ion transport in a toroidal magnetized turbulent plasma. Measurements in the superdiffusive regime are characterized by a higher intermittency than in the subdiffusive regime. Using conditional averaging, we show that, when the transport is superdiffusive, suprathermal ions are transported by intermittent field-elongated turbulent structures that are radially propagating.
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Affiliation(s)
- A Bovet
- École Polytechnique Fédérale de Lausanne (EPFL), Centre de Recherches en Physique des Plasmas (CRPP), CH-1015 Lausanne, Switzerland
| | - A Fasoli
- École Polytechnique Fédérale de Lausanne (EPFL), Centre de Recherches en Physique des Plasmas (CRPP), CH-1015 Lausanne, Switzerland
| | - I Furno
- École Polytechnique Fédérale de Lausanne (EPFL), Centre de Recherches en Physique des Plasmas (CRPP), CH-1015 Lausanne, Switzerland
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