Observation of Alfvén eigenmodes driven by fast electrons during lower hybrid wave heating in EAST plasmas

Hu, Wenhui; Li, Jiangang; Xiao, Bingjia; Heidbrink, W. W.; Shi, Tonghui; Hu, Youjun; Chen, Jiale; Spong, D. A.; Liu, Haiqing; Wang, Shouxin; Lin, Shiyao; Li, Yongliang; Yuan, Yifei; Zhou, Ruijie

doi:10.1088/1741-4326/aacfad

Cited by 8 publications

(13 citation statements)

References 26 publications

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“…Most regions of the plasmas studied in this work are heated by both NBI and low input power of 4.6 GHz lower hybrid wave (LHW) (P lhw ∼ 1 MW) simultaneously. However, the plasma parameters are not consistent with the region where AEs can be excited by energetic electrons [17].…”

Section: Experimental Setup and Diagnosticsmentioning

confidence: 83%

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Investigation of Alfvén eigenmodes and Energetic Particle Modes in EAST with neutral beam injection

Xu¹,

Shen²,

Ren³

et al. 2021

Nucl. Fusion

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Alfvén eigenmodes (AEs) and energetic particle modes (EPMs) have been observed in EAST neutral beam injection plasma with the presence of heavy tungsten impurity in the core region. The AEs are identified as toroidal Alfvén eigenmodes (TAEs) with roughly constant frequency f TAE ∼ 100 kHz and a special set of AEs with frequency chirping up from frequency f AE ∼ 70 kHz to f AE ∼ 100 kHz. The frequency of EPMs is around f EPM ∼ 60 kHz, exhibiting with frequency chirping down feature. A transition from EPMs to AEs is found, and the location and mode numbers are measured by experimental diagnostics. Hybrid simulations with the global kinetic-magnetohydrodynamic code M3D-K have been carried out to investigate the observed AEs and EPMs, and linear simulations find the EPM with toroidal mode number n = 2 and poloidal mode number m = 3. Nonlinear simulations show that the EPM frequency chirps down nonlinearly, and then two modes emerge with frequencies around 72.7 kHz and 88.0 kHz: the mode with higher frequency is a TAE, and the other mode is an EPM. Afterward, the TAE disappears quickly with the frequency almost unchanged, and the EPM with lower frequency chirps down continuously. The mode frequencies and locations of the simulated EPM and TAE, as well as the chirping down feature of the EPM frequency, are consistent with the experimental measurements. The transition from EPM to TAE is found to be a self-consistent dynamic of nonlinear evolution with the expel of energetic ions due to EPM.

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Section: Experimental Setup and Diagnosticsmentioning

confidence: 83%

“…ECRH could be a candidate to suppress/control AEs. In EAST tokamak, energetic electrons driven TAEs have been studied in lower hybrid current driven (LHCD) plasma [17,18] and in electron cyclotron current drive plasma [19]. In LHCD plasma with a relative low density, BAE is also found to be excited by energetic electrons [20].…”

Section: Introductionmentioning

confidence: 99%

Investigation of Alfvén eigenmodes and Energetic Particle Modes in EAST with neutral beam injection

Xu¹,

Shen²,

Ren³

et al. 2021

Nucl. Fusion

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“…These destabilized modes during ECRH mainly propagate in the electron diamagnetic drift direction. Energetic electrons generated by LHW can also destabilize AEs [25,26]. In EAST LHW experiment [26], the observed AEs can propagate in either ion or electron diamagnetic drift direction.…”

Section: Introductionmentioning

confidence: 97%

“…Energetic electrons generated by LHW can also destabilize AEs [25,26]. In EAST LHW experiment [26], the observed AEs can propagate in either ion or electron diamagnetic drift direction. In addition, it was recently reported that energetic electrons induced by static magnetic perturbations can also drive a TAE propagating in the ion diamagnetic drift direction [27].…”

Section: Introductionmentioning

confidence: 97%

Simulation of Alfvén eigenmodes destabilized by energetic electrons in tokamak plasmas

Todo

Wang

2020

Nucl. Fusion

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Alfvén eigenmodes (AEs) driven by energetic electrons were investigated via hybrid simulations of an MHD fluid interacting with energetic electrons. The investigation focused on AEs with the toroidal number n = 4. Both energetic electrons with centrally peaked beta profile and off-axis peaked profile are considered. For the centrally peaked energetic electron beta profile case, a toroidal Alfvén eigenmode (TAE) propagating in the electron diamagnetic drift direction is found. The mode is mainly driven by deeply trapped energetic electrons. It is also found that a few passing energetic electrons spatially localized around rational surfaces can resonate with the mode. For the off-axis peaked energetic electron beta profile case, an AE propagating in the ion diamagnetic drift direction is found when a q − p r o f i l e with weak magnetic shear is adopted. The destabilized mode is an elliptical-Alfvén-eigenmode-type (EAE-type) mode which has a spatial profile peaking at the rational surface and a frequency close to the second Alfvén frequency gap. It is found that passing energetic electrons and barely trapped energetic electrons are responsible for this EAE-type mode destabilization. The saturation levels are compared for a TAE with the same linear growth rate among energetic electron driven mode and energetic ion driven mode with isotropic and anisotropic velocity space distributions. The saturation level of TAE driven by trapped energetic electrons is comparable to that driven by energetic electrons with isotropic velocity space distribution where the contribution of trapped particles is dominant. It is found that the trapped energetic ion driven TAE has a larger saturation level than the passing energetic ion driven TAE, which indicates the difference in particle trapping by the TAE between trapped and passing energetic ions.

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“…In particular, in HL-2A tokamak experiments, the MHD instabilities of SAW type propagating in the electron diamagnetic drift direction were analyzed during the electron cyclotron resonance heating phase (ECRH), such as the EE-driven beta-induced Alfvén eigenmode (e-BAE) and EE-driven toroidal Alfvén eigenmode (e-TAE) [12][13][14][15]. In EAST, EEs generated by lower hybrid wave (LHW) heating in L-mode plasmas and induced by static magnetic perturbations in ohmic heating plasmas have been found to destabilize TAEs [16,17]. These experimental observations have revealed part of the linear properties of EE-driven AE instabilities, including frequency, toroidal mode number and propagation direction.…”

Section: Introductionmentioning

confidence: 99%

Multiple Alfvén eigenmodes induced by energetic electrons and nonlinear mode couplings in EAST radio-frequency heated H-mode plasmas

et al. 2021

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Multiple electromagnetic coherent modes with frequencies f ∼ 20–300 kHz and toroidal mode numbers n = 1 and n = 2 have been observed and investigated in radio-frequency heated H-mode plasmas of the EAST tokamak. The experimental results show that the two main branches of these coherent modes are driven by energetic electrons (EEs), which are produced in the processes of radio-frequency current drive and heating. Bicoherence analysis indicates that there are strong nonlinear mode interactions between the two branches (mother waves), i.e. one is in the low-frequency range of f ∼ 20–50 kHz and the other one is in the high-frequency range of f ∼ 120–250 kHz, and their nonlinear couplings can generate many harmonics (daughter waves). Both coherent modes propagate poloidally along the electron diamagnetic drift direction. The gyrokinetic eigenvalue simulations support the view that both the low-frequency and the high-frequency coherent modes observed in EAST are Alfvén eigenmode (AE) type, and the kinetic effects of background plasmas and EEs are responsible for the formation and excitation of AEs, respectively. The low-frequency coherent mode is identified as the kinetic beta-induced Alfvén eigenmode located in the edge, and the high-frequency coherent mode is radially global, which is characterized by a toroidal Alfvén eigenmode (TAE) in the core and also has the components of a kinetic TAE and ellipticity-induced Alfvén eigenmode in the outer region due to the large downshift of the Alfvén continuum gap from the core to the edge in H-mode discharges.

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Observation of Alfvén eigenmodes driven by fast electrons during lower hybrid wave heating in EAST plasmas

Cited by 8 publications

References 26 publications

Investigation of Alfvén eigenmodes and Energetic Particle Modes in EAST with neutral beam injection

Investigation of Alfvén eigenmodes and Energetic Particle Modes in EAST with neutral beam injection

Simulation of Alfvén eigenmodes destabilized by energetic electrons in tokamak plasmas

Multiple Alfvén eigenmodes induced by energetic electrons and nonlinear mode couplings in EAST radio-frequency heated H-mode plasmas

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