Excitation of toroidal Alfvén eigenmode by barely circulating energetic electrons in low density plasmas

Wang, Tao; Zhu, Xiang; Zeng, Long; Briguglio, S.; Vlad, G.; Zonca, F.; Qiu, Zhiyong

doi:10.1088/1361-6587/acc6ee

Cited by 4 publications

(3 citation statements)

References 42 publications

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“…We also notice that the resonance between barelycirculating EE and TAE has been identified as the dominant mechanism of TAE driven by EEs in a recent work [26], for comparison, both barely-and well-circulating EE are resonant with EAE that attribute to m and m + 2 poloidal harmonic coupling at q = (m + 1) /n. In addition, according to figure 11, the resonance lines for the well-circulating EEs can extend in a wide range of λ pitch angle, which indicates that abundant resonant EEs are responsible for EAE excitation, in consistent with early MEGA simulations as shown by figure 12 of [25].…”

Section: Destabilization Mechanismsupporting

confidence: 56%

“…Additionally, from the theoretical and numerical simulations perspectives, many efforts have been made to understand the destabilization mechanisms of Alfvén instabilities by EEs. And these results reveal that both trapped (deeply and barely) and circulating (well and barely) EEs can excite the Alfvén instabilities when appropriate resonance conditions are satisfied [25,26]. However, regarding to realistic experiments, EE-driven AE problems could be complicated by the synergy of wave-wave and wave-particle interactions in multiple channels, non-perturbative effects, and complex geometry.…”

Section: Introductionmentioning

confidence: 93%

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Bursting core-localized ellipticity-induced Alfvén eigenmodes driven by energetic electrons during EAST ohmic discharges

Su,

Lan,

Zhou

et al. 2024

Nucl. Fusion

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A series of high-frequency (400~1000 kHz) bursting core-localized Alfvén instabilities have been observed during ohmic discharges in EAST tokamak. The instability trigger favours the discharge conditions of low toroidal magnetic field and low electron density. The toroidal mode numbers are mainly n=2~3 and they propagate in the ion diamagnetic drift (co-current) direction. These modes are radially localized in the range of ρ_tor=0.2~0.35 based on Doppler BackScatter (DBS) measurement. They are identified as ellipticity-induced Alfvén eigenmodes (EAEs) occurring at q=1 rational surfaces by magnetohydrodynamics (MHD) simulations using the realistic geometry and plasma profiles. The EAEs show regular bursts with ~10 milliseconds duration along with the mode frequency chirping downwards and upwards rapidly. It is also found that sawtooth events can interrupt the growth and evolution of the EAEs, causing the modes to disappear immediately. Passing energetic electrons (EEs) that move much faster than Alfvén velocity are responsible for the destabilization of these EAEs, which attribute to the fact that the large poloidal and toroidal frequencies mostly cancel each other and satisfy the EAE resonance condition with primary energy exchange. These novel experimental results of the wave-particle interaction between EAEs and EEs are helpful for extrapolating alpha particle physics that are characterized by small orbit width with respect to machine size in future fusion reactors.

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Section: Destabilization Mechanismsupporting

confidence: 56%

Section: Introductionmentioning

confidence: 93%

Bursting core-localized ellipticity-induced Alfvén eigenmodes driven by energetic electrons during EAST ohmic discharges

Su,

Lan,

Zhou

et al. 2024

Nucl. Fusion

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“…Meanwhile, the coupling scheme of EE and bulk plasma can be used for other EE distributions and/or full EE dynamics in phase space, e.g. showing-down distribution and barely circulating/trapped EEs [48]. in ITER has small dimensionless orbit that is similar to EE in EAST, which indicates that both alpha particle and EE interact with waves locally in the radial direction of tokamak, in contrast the orbit width of 60 keV NBI ion in DIII-D is on the same order of minor radius, resulting in additional physics associated to nonlocal effects [13].…”

Section: Discussionmentioning

confidence: 99%

Global simulations of kinetic-magnetohydrodynamic processes with energetic electrons in tokamak plasmas

Bao,

Zhang,

et al. 2023

Nucl. Fusion

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The energetic electrons (EEs) produced from auxiliary heatings have been found to destabilize various Alfven eigenmodes (AEs) in recent experiments. To investigate EE relevant kinetic-magnetohydrodynamic (MHD) processes, a global fluid-kinetic hybrid model is formulated and verified in this work, which consists of Landau-fluid bulk plasmas and drift-kinetic EEs that incorporates the dominant damping and drive mechanisms, respectively. The numerical capability of Landau-fluid bulk plasmas is obtained based on a well-benchmarked eigenvalue code MAS using general geometry (Bao et al 2023 Nucl. Fusion $\bm{63}$ 076021), and the comprehensive EE responses to the low frequency ($\omega\ll\Omega_{ci}$) MHD fluctuations are analytically derived and implemented in MAS, which not only cover contributions from trapped and passing particles, but also take into account the effects of adiabatic fluid convection and non-adiabatic kinetic compression. The linear properties of EE-driven beta-induced Alfven eigenmodes (e-BAE) are systematically studied using both MAS model and GTC particle-in-cell simulations. Building on the good agreements on the mode structure and dispersion relation, several key issues of e-BAE physics are analyzed and discussed, including the parametric dependences of e-BAE stability on EE mass, temperature and density with corresponding phase space dynamics, EE non-perturbative effects on the symmetry breaking of mode structure, and the EE density and temperature thresholds for e-BAE excitation that overcome bulk plasma damping. With these efforts, the upgraded MAS model is superior than initial-value simulations restricted by stringent electron Courant condition for the fast linear analyses of most EE-AE problems with $\omega\ll\Omega_{ci}$, of which wave-particle resonance can be used to analyze the analogous effect of alpha particle driven AEs in future fusion reactor.

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Toroidal Alfvén mode instability driven by plasma current in low-density Ohmic plasmas of the spherical tori

Marchenko,

Reznik

2024

Physics of Plasmas

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Due to intrinsically low magnetic fields, at low density the drift speed of the current-carrying electrons in spherical tokamaks can exceed fraction of the Alfvén speed sufficient for the excitation of the Alfvén gap modes. A particular case of the toroidal mode, observed during minor disruptions in Ohmic shots on SUNIST [Liu et al., Phys. Plasmas 23, 120706 (2016)], is considered in the present communication. Due to the negligible effect of the electron pressure gradient, the growth rate scales linearly with the drift speed, with slope inversely proportional to electron thermal velocity. In the absence of continuum damping, the threshold value of the drift speed for TAE excitation is independent of electron temperature.

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Excitation of toroidal Alfvén eigenmode by barely circulating energetic electrons in low density plasmas

Cited by 4 publications

References 42 publications

Bursting core-localized ellipticity-induced Alfvén eigenmodes driven by energetic electrons during EAST ohmic discharges

Bursting core-localized ellipticity-induced Alfvén eigenmodes driven by energetic electrons during EAST ohmic discharges

Global simulations of kinetic-magnetohydrodynamic processes with energetic electrons in tokamak plasmas

Toroidal Alfvén mode instability driven by plasma current in low-density Ohmic plasmas of the spherical tori

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