title: Strong Destabilization of Stable Modes with a Half-Frequency Associated with Chirping Geodesic Acoustic Modes in the Large Helical Device.
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.
authors.affiliation: National Institute for Fusion Science, 322-6 Oroshi, Toki, Gifu 509-5292, Japan.
authors.forename: T
authors.initials: T
authors.lastname: Ido
authors.affiliation: National Institute for Fusion Science, 322-6 Oroshi, Toki, Gifu 509-5292, Japan.
authors.forename: K
authors.initials: K
authors.lastname: Itoh
authors.affiliation: 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.
authors.forename: M
authors.initials: M
authors.lastname: Osakabe
authors.affiliation: Research Institute for Applied Mechanics, Kyushu University, 6-1 Kasuga-koen, Kasuga, Fukuoka 816-8580, Japan.
authors.forename: M
authors.initials: M
authors.lastname: Lesur
authors.affiliation: National Institute for Fusion Science, 322-6 Oroshi, Toki, Gifu 509-5292, Japan.
authors.forename: A
authors.initials: A
authors.lastname: Shimizu
authors.affiliation: 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.
authors.forename: K
authors.initials: K
authors.lastname: Ogawa
authors.affiliation: National Institute for Fusion Science, 322-6 Oroshi, Toki, Gifu 509-5292, Japan.
authors.forename: K
authors.initials: K
authors.lastname: Toi
authors.affiliation: Graduate School of Frontier Sciences, University of Tokyo, 5-1-5 Kashiwanohara, Kashiwa, Chiba 277-8561, Japan.
authors.forename: M
authors.initials: M
authors.lastname: Nishiura
authors.affiliation: National Institute for Fusion Science, 322-6 Oroshi, Toki, Gifu 509-5292, Japan.
authors.forename: S
authors.initials: S
authors.lastname: Kato
authors.affiliation: Research Institute for Applied Mechanics, Kyushu University, 6-1 Kasuga-koen, Kasuga, Fukuoka 816-8580, Japan.
authors.forename: M
authors.initials: M
authors.lastname: Sasaki
authors.affiliation: 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.
authors.forename: K
authors.initials: K
authors.lastname: Ida
authors.affiliation: Research Institute for Applied Mechanics, Kyushu University, 6-1 Kasuga-koen, Kasuga, Fukuoka 816-8580, Japan.
authors.forename: S
authors.initials: S
authors.lastname: Inagaki
authors.affiliation: Research Institute for Applied Mechanics, Kyushu University, 6-1 Kasuga-koen, Kasuga, Fukuoka 816-8580, Japan.
authors.forename: S-I
authors.initials: SI
authors.lastname: Itoh