{"id":7798,"date":"2024-06-14T10:05:01","date_gmt":"2024-06-14T01:05:01","guid":{"rendered":"https:\/\/unit.nifs.ac.jp\/research\/?post_type=report&p=7798"},"modified":"2024-10-10T11:46:24","modified_gmt":"2024-10-10T02:46:24","slug":"report-7781_en","status":"publish","type":"report","link":"https:\/\/unit.nifs.ac.jp\/research\/archives\/report\/report-7781_en","title":{"rendered":"Nonlinear excitation of energetic particle driven geodesic acoustic mode by Alfv\u00e9n instability in ASDEX-Upgrade Tokamak"},"content":{"rendered":"\n

Recently, the coexistence of multiple energetic particle driven instabilities was observed in experiments on the ASDEX-Upgrade tokamak. A hybrid simulation using the MEGA code was performed to investigate the properties of those instabilities. It is found that the energetic particle driven geodesic acoustic mode (EGAM) is initially stable, then zonal flow gradually occurs with the growth of the Alfv\u00e9n instability, and finally, the EGAM is nonlinearly excited and the amplitude exceeds that of the Alfv\u00e9n instability. The mode properties of the nonlinearly excited EGAM are quite different from linearly excited EGAM. For the linearly excited EGAM, the frequency can be higher than conventional geodesic acoustic mode frequency, but only under the condition of bump-on-tail energetic particle distribution. Interestingly, the higher frequency holds true even under the condition of a slowing-down energetic particle distribution for the nonlinearly excited EGAM. This difference is because when the EGAM is nonlinearly excited, the energetic particle distribution function changes from its initial distribution due to the Alfv\u00e9n instability. This change in the distribution function affects the properties of the EGAM.<\/p>\n\n\n\n

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Figure: The time evolution of the Alfv\u00e9n instability (green) and the EGAM (red) at (a) the initial stage, (b) the linear growth stage and (c) the whole stage. In figure (a), in order to better observe the change in EGAM, the amplitude of the red curve is increased by a factor of 4 when plotting.<\/figcaption><\/figure>\n<\/div>\n\n\n
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The numerical simulations were performed on Plasma Simulator of NIFS, JFRS-1 of IFERC-CSC, and Fugaku of R-CCS.<\/p>\n\n\n\n

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\u3010Publication\u3011<\/p>\n\n\n\n

Hao WANG, Philipp W. LAUBER, Yasushi TODO, Yasuhiro SUZUKI, Hanzheng LI, Jialei WANG, and Shizhao WEI, \u201cNonlinear excitation of energetic particle driven geodesic acoustic mode by Alfv\u00e9n instability in ASDEX-Upgrade Tokamak\u201d, Nuclear Fusion 64 (2024), 076015.<\/a><\/p>\n\n\n\n

DOI: 10.1088\/1741-4326\/ad4a8d<\/a><\/p>\n\n\n\n

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