High frequency mode generation by toroidal Alfvén eigenmodes

Wei, Shizhao; Shi, P.W.; Yu, Liming; Chen, Wei; Chen, Ningfei; Qiu, Zhiyong

doi:10.1063/1.5100597

Cited by 4 publications

(4 citation statements)

References 45 publications

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“…The highfrequency mode 𝛺 h (𝜔 h , 𝑘 h ) excited by two TAEs, 𝛺 1 (𝜔 1 , 𝑘 1 ) and 𝛺 1 (𝜔 2 , 𝑘 2 ), with opposite toroidal mode numbers can be investigated by nonlinear gyrokinetic theory. [81] In our experiment, 𝜔 1 ≃ 𝜔 2 and 𝑛 1 = −𝑛 2 for the TAEs while the axisymmetric mode with 𝜔 ≈ 𝑉 A /𝑞𝑅. The wave number and frequency matching condition during mode coupling process are…”

Section: Nonlinear Coupling Between Alfvénic Modes and Tearingmentioning

confidence: 61%

Energetic Particle Physics on the HL-2A Tokamak: A Review

Shi¹,

Chen²,

Duan³

2021

Chinese Phys. Lett.

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Interaction between shear Alfvén wave (SAW) and energetic particles (EPs) is one of major concerns in magnetically confined plasmas since it may lead to excitation of toroidal symmetry breaking collective instabilities, thus enhances loss of EPs and degrades plasma confinement. In the last few years, Alfvénic zoology has been constructed on HL-2A tokamak and series of EPs driven instabilities, such as toroidal Alfvén eigenmodes (TAEs), revered shear Alfvén eigenmodes (RSAEs), beta induced Alfvén eigenmodes (BAEs), Alfvénic ion temperature gradient (AITG) modes and fishbone modes, have been observed and investigated. Those Alfvénic fluctuations show frequency chirping behaviors through nonlinear wave-particle route, and contribute to generation of axisymmetric modes by nonlinear wave-wave resonance in the presence of strong tearing modes. It is proved that the plasma confinement is affected by Alfvénic activities from multiple aspects. The RSAEs resonate with thermal ions, and this results in an energy diffusive transport process while the nonlinear mode coupling between core-localized TAEs and tearing modes trigger avalanche electron heat transport events. Effective measures have been taken to control SAW fluctuations and the fishbone activities are suppressed by electron cyclotron resonance heating. Those experimental results will not only contribute to better understandings of energetic particles physics, but also provide technology bases for active control of Alfvénic modes on International Thermonuclear Experimental Reactor (ITER) and Chinese Fusion Engineering Testing Reactor (CFETR).

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Section: Nonlinear Coupling Between Alfvénic Modes and Tearingmentioning

confidence: 61%

Energetic Particle Physics on the HL-2A Tokamak: A Review

Shi¹,

Chen²,

Duan³

2021

Chinese Phys. Lett.

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“…Meanwhile, various nonideal effects, notably the magnetic geometry, plasma nonuniformity, compressibility and kinetic effects, could break such a 'pure Alfvénic state' [1] and lead to nonlinear spectral energy transfer by coupling with other collective oscillations [2,58,63]. These nonideal effects, which must be accounted for when studying SAW instability nonlinear dynamics and EP transport in burning plasmas, have been intensively investigated using TAE as a paradigm case [51,[120][121][122][123][124][125][126][127], as recently reviewed in [128]. The developed theoretical framework and obtained insights can be straightforwardly applied to other kinds of SAW instabilities, e.g., RSAE, which is the subject of this section, based on the understanding of RSAE linear physics and saturation due to wave-particle interactions as reviewed in section 2.…”

Section: Nonlinear Wave-wave Couplingsmentioning

confidence: 99%

Nonlinear dynamics of the reversed shear Alfvén eigenmode in burning plasmas

WANG 王,

WEI 魏,

BRIGUGLIO

et al. 2024

Plasma Sci. Technol.

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In a tokamak fusion reactor operated at steady state, the equilibrium magnetic field is likely to have reversed shear in the core region, as the noninductive bootstrap current profile generally peaks off-axis. The reversed shear Alfvén eigenmode (RSAE) as a unique branch of the shear Alfvén wave in this equilibrium, can exist with a broad spectrum in wavenumber and frequency, and be resonantly driven unstable by energetic particles (EP). After briefly discussing the RSAE linear properties in burning plasma condition, we review several key topics of the nonlinear dynamics for the RSAE through both wave-EP resonance and wave-wave coupling channels, and illustrate their potentially important role in reactor-scale fusion plasmas. By means of simplified hybrid MHD-kinetic simulations, the RSAEs are shown to have typically broad phase space resonance structure with both circulating and trapped EP, as results of weak/vanishing magnetic shear and relatively low frequency. Through the route of wave-EP nonlinearity, the dominant saturation mechanism is mainly due to the transported resonant EP radially decoupling with the localized RSAE mode structure, and the resultant EP transport generally has a convective feature. The saturated RSAEs also undergo various nonlinear couplings with other collective oscillations. Two typical routes as parametric decay and modulational instability are studied using nonlinear gyrokinetic theory, and applied to the scenario of spontaneous excitation by a finite amplitude pump RSAE. Multiple RSAEs could naturally couple and induce the spectral energy cascade into a low frequency Alfvénic mode, which may effectively transfer the EP energy to fuel ions via collisionless Landau damping. Moreover, zero frequency zonal field structure could be spontaneously excited by modulation of the pump RSAE envelope, and may also lead to saturation of the pump RSAE by both scattering into stable domain and local distortion of the continuum structure.

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“…Meanwhile, squared bicoherence reveals that the high frequency n = 0 modes are made up of two AMs with (n AM1 , n AM2 ) = (−1, 1)/(−2, 2)/(−3, 3), i.e. the axisymmetric mode in the EAE frequency range is driven by nonlinear coupling of two co-/counter-propagating AMs [26,27], rather than the second harmonic of Alfvénic mode with n = 0 in the TAE frequency range.…”

Section: Nonlinear Mode Coupling Between Tae and Tearing Modementioning

confidence: 99%

Observation of off-axis sawtooth oscillations during the presence of nonlinear mode couplings in HL-2A NBI heated plasmas

et al. 2021

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Off-axis sawtooth oscillations during the presence of nonlinear coupling between toroidal Alfvén eigenmodes (TAEs) and tearing mode are firstly observed in the plasma without two q = 2 rational surfaces on HL-2A tokamak. Those low frequency oscillations always take place followed by nonlinear interaction processes and the off-axis features have been confirmed by multiple diagnostics, such as soft x-ray arrays and electron cyclotron emission imaging systems. A possible physical mechanism is proposed for interpretation of those off-axis oscillations. That is, nonlinear interaction between TAEs and tearing mode causes significant losses of fast ions though the spacial overlapped global mode structure, then makes a drop in torque and leads to rotation braking or even mode locking. When magnetic fluctuation becomes large enough during braking or locking, the resulting high amplitude saturated mode leads to subsequent or immediate collapse at the q = 2 rational surface.

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High frequency mode generation by toroidal Alfvén eigenmodes

Cited by 4 publications

References 45 publications

Energetic Particle Physics on the HL-2A Tokamak: A Review

Energetic Particle Physics on the HL-2A Tokamak: A Review

Nonlinear dynamics of the reversed shear Alfvén eigenmode in burning plasmas

Observation of off-axis sawtooth oscillations during the presence of nonlinear mode couplings in HL-2A NBI heated plasmas

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