Chirping and Sudden Excitation of Energetic-Particle-Driven Geodesic Acoustic Modes in a Large Helical Device Experiment

Wang, Hao; Todo, Y.; Ido, T.; Suzuki, Yasuhiro

doi:10.1103/physrevlett.120.175001

Cited by 30 publications

(36 citation statements)

References 28 publications

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“…The secondary mode can be nonlinearly driven unstable as the primary mode frequency approaches twice the secondary mode frequency (which is close to the local GAM frequency), which minimizes the threshold due to frequency mismatch. The interpretation is consistent with the crucial elements from experimental observation [37] and numerical simulation [39]; thus, it provides and illuminates the underlying physics picture.…”

Section: Introductionsupporting

confidence: 81%

“…It was further found [37] that, as the high frequency EGAM (will be denoted as "primary EGAM" in the rest of the paper for apparent reasons) chirped up to twice local GAM frequency, possibly as a result of the EGAM induced pitch angle scattering to lower pitch angle and thus higher v domain, a "secondary mode" could be strongly driven unstable, with the frequency close to the local GAM frequency [37]. The experimental observations are nicely recovered in a MHD-kinetic hybrid simulation using MEGA code [38,39], and it is found that, besides the secondary mode strong excitation, the EPs "driving" the secondary mode are the same as those linearly driving the primary EGAM, though the secondary mode frequency is only half of that of the primary mode. It is also found that the secondary mode generation still persists when the "fluid nonlinearity" is turned off; and, as the primary mode frequency keeps chirping up, the secondary mode frequency is almost unchanged, suggesting it is a normal mode of the system itself.…”

Section: Introductionmentioning

confidence: 99%

“…One speculation by Ref. [39] is that the secondary mode is driven by "nonlinear resonance" [40,41], which, however, is typically associated with finite amplitude fluctuations, and is not satisfied in the condition for the onset of the secondary mode.…”

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

Evidence of "Two Plasmon" decay of energetic particle induced geodesic acoustic mode

Qiu,

Chen,

Zonca

et al. 2021

Preprint

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Secondary low frequency mode generation by energetic particle induced geodesic acoustic mode (EGAM) observed in LHD experiment is studied using nonlinear gyrokinetic theory. It is found that the EGAM frequency can be significantly higher than local geodesic acoustic mode (GAM) frequency in low collisionality plasmas, and it can decay into two GAMs as its frequency approaches twice GAM frequency, in a process analogous to the well-known two plasmon decay instability. The condition for this process to occur is also discussed.

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Section: Introductionsupporting

confidence: 81%

Section: Introductionmentioning

confidence: 99%

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Evidence of "Two Plasmon" decay of energetic particle induced geodesic acoustic mode

Qiu,

Chen,

Zonca

et al. 2021

Preprint

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“…The time evolution of energetic particle driven geodesic acoustic modes (EGAMs) is often accompanied by the frequency chirping (Boswell et al 2006;Nazikian et al 2008;Ido et al 2016). The frequency chirping and the sudden excitation of EGAMs observed in LHD experiments were successfully reproduced by kinetic MHD hybrid simulations (Wang et al , 2018. Though the reduced simulation model may not be applied to the EGAMs for which energetic particles have the non-perturbative effects on the real frequency and the spatial profile, the creation of hole and clump was demonstrated for a chirping EGAM with the kinetic MHD hybrid simulation .…”

Section: Hole-clump Creation and Frequency Chirpingmentioning

confidence: 94%

Introduction to the interaction between energetic particles and Alfven eigenmodes in toroidal plasmas

Todo

2018

Rev. Mod. Plasma Phys.

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This article is a tutorial review of the interaction between energetic particles and Alfvén eigenmodes (AEs) which is one of the important research issues for fusion burning plasmas. The destabilization mechanism of AEs is a kind of inverse Landau damping through the resonant interaction with energetic particles. The important properties of the AE instability, such as resonance condition, conserved variable during the interaction, and particle trapping by the AE, are explained. The time evolution of AEs is classified into various types, steady state, frequency splitting, frequency chirping, and recurrent bursts. Berk and Breizman presented both a onedimensional weakly nonlinear theory for marginal stability and a reduced simulation model that qualitatively explain the various types of time evolution. Berk-Breizman's theory and reduced simulation model are introduced, and their limitations and the future works are discussed in this article. In addition, energetic particle transport by AEs is illustrated with surface-of-section plots. The particle trapping by the AE creates phase space islands and leads to the local flattening of the energetic particle spatial profile. The resonance overlap of multiple AEs and the overlap of higherorder resonances of a single AE lead to the emergence of stochasticity in phase space and the global transport of energetic particles.

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“…The sudden excitation of the half-frequency EGAM during the frequency chirping of the primary EGAM was reproduced, and the triggering mechanism through the nonlinear resonance overlap was discovered (Wang et al. 2018). The MEGA code has been extended with kinetic thermal ions.…”

Section: Introductionmentioning

confidence: 99%

Hybrid simulation of NBI fast-ion losses due to the Alfvén eigenmode bursts in the Large Helical Device and the comparison with the fast-ion loss detector measurements

et al. 2020

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The multiphase simulations are conducted with the kinetic-magnetohydrodynamics hybrid code MEGA to investigate the spatial and the velocity distributions of lost fast ions due to the Alfvén eigenmode (AE) bursts in the Large Helical Device plasmas. It is found that fast ions are lost along the divertor region with helical symmetry both before and during the AE burst except for the promptly lost particles. On the other hand, several peaks are present in the spatial distribution of lost fast ions along the divertor region. These peaks along the divertor region can be attributed to the deviation of the fast-ion orbits from the magnetic surfaces due to the grad-B and the curvature drifts. For comparison with the velocity distribution of lost fast ions measured by the fast-ion loss detector (FILD), the ‘numerical FILD’ which solves the Newton–Lorentz equation is constructed in the MEGA code. The velocity distribution of lost fast ions detected by the numerical FILD during AE burst is in good qualitative agreement with the experimental FILD measurements. During the AE burst, fast ions with high energy (100–180 keV) are detected by the numerical FILD, while co-going fast ions lost to the divertor region are the particles with energy lower than 50 keV.

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Chirping and Sudden Excitation of Energetic-Particle-Driven Geodesic Acoustic Modes in a Large Helical Device Experiment

Cited by 30 publications

References 28 publications

Evidence of "Two Plasmon" decay of energetic particle induced geodesic acoustic mode

Evidence of "Two Plasmon" decay of energetic particle induced geodesic acoustic mode

Introduction to the interaction between energetic particles and Alfven eigenmodes in toroidal plasmas

Hybrid simulation of NBI fast-ion losses due to the Alfvén eigenmode bursts in the Large Helical Device and the comparison with the fast-ion loss detector measurements

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