Properties of toroidal Alfvén eigenmode in DIII-D plasma

Wang, Zhixuan; Zhang, Lin; Deng, Wenjun; Holod, I.; Heidbrink, W. W.; Xiao, Yong; Zhang, H.; Zhang, W.; Zeeland, Michael Van

doi:10.1063/1.4908274

Cited by 27 publications

(41 citation statements)

References 55 publications

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“…The Gyrokinetic Toroidal Code (GTC) 5 treats a population of bulk ions and a separate population of energetic ions with the δf particle-in-cell method (though a full-f method is also available). For a full description of the 5D system of equations solved by GTC, see Ref [11][12][13][14]. The electrons are treated in the present work with a fluidkinetic model either purely analytically (therefore fully adiabatic) or analytically with a kinetic component (a hybrid kinetic approach) as specified.…”

Section: Details Of Gyrokinetic Simulationsmentioning

confidence: 99%

Gyrokinetic simulations of toroidal Alfvén eigenmodes excited by energetic ions and external antennas on the Joint European Torus

et al. 2018

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The Gyrokinetic Toroidal Code (GTC) has been used to study Toroidal Alfvén Eigenmodes (TAEs) in highperformance plasmas. Experiments performed at the Joint European Torus, where TAEs were driven by energetic particles arising from Neutral Beams, ion cyclotron resonant heating and resonantly excited by dedicated external antennas, have been simulated. Modes driven by populations of energetic particles are observed, matching the TAE frequency seen with magnetic probes. A synthetic antenna, composed of one toroidal and two neighboring poloidal harmonics has been used to probe the modes' damping rates and quantify mechanisms for this damping. This method was also applied to frequency and damping rate measurements of stable TAEs made by the Alfvén Eigenmode Active Diagnostic in these discharges.

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Section: Details Of Gyrokinetic Simulationsmentioning

confidence: 99%

Gyrokinetic simulations of toroidal Alfvén eigenmodes excited by energetic ions and external antennas on the Joint European Torus

et al. 2018

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Section: © Eurofusionmentioning

confidence: 99%

“…Mode saturation is due to a mechanism called radial decoupling [26,27], corresponding to the flattening process extending over the whole radial region where the mode structure is localised. Further increasing the drive (EPM regime) causes the EP contribution to become fully nonperturbative and able to determine both mode frequency and radial structure [8,9,[28][29][30].In a recent review paper [22], a systematic theoretical framework of EP physics is presented, including a detailed discussion of the nonlinear wave-particle interactions between Alfvén modes with EPs. In the present paper, we investigate, by means of numerical simulations, the occurrence of different saturation mechanisms for a single-toroidal-number gap mode in different EP drive regimes.In section 2, we present an introduction to the single mode problem.…”

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Saturation of single toroidal number Alfvén modes

Wang

Briguglio

2016

New J. Phys.

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The results of numerical simulations are presented to illustrate the saturation mechanism of a single toroidal number Alfvén mode, driven unstable, in a tokamak plasma, by the resonant interaction with energetic ions. The effects of equilibrium geometry non-uniformities and finite mode radial width on the wave-particle nonlinear dynamics are discussed. Saturation occurs as the fast-ion density flattening produced by the radial flux associated to the resonant particles captured in the potential well of the Alfvén wave extends over the whole region where mode-particle power exchange can take place. The occurrence of two different saturation regimes is shown. In the first regime, dubbed resonance detuning, that region is limited by the resonance radial width (that is, the width of the region where the fast-ion resonance frequency matches the mode frequency). In the second regime, called radial decoupling, the power exchange region is limited by the mode radial width. In the former regime, the mode saturation amplitude scales quadratically with the growth rate; in the latter, it scales linearly. The occurrence of one or the other regime can be predicted on the basis of linear dynamics: in particular, the radial profile of the fast-ion resonance frequency and the mode structure. Here, we discuss how such properties can depend on the considered toroidal number and compare simulation results with the predictions obtained from a simplified nonlinear pendulum model.Original content from this work may be used under the terms of the Creative Commons Attribution 3.0 licence.Any further distribution of this work must maintain attribution to the author(s) and the title of the work, journal citation and DOI. © EUROfusionunstable. As the EP pressure gradient exceeds a certain threshold, even strongly damped continuum oscillations, besides these normal modes of the background plasma, can be driven unstable; they are called energetic particle modes (EPM) [3]. Alvénic fluctuations of various types, excited by EPs, have been identified in several tokamak experiments [4][5][6][7][8][9].Linear properties of Alfvénic fluctuations driven by EPs can be investigated within the theoretical framework of the generalised fishbone-like dispersion relation [3,10,11]. On this basis, several successful comparison between theoretical predictions and experimental observations, as well as numerical simulation results, have been reported [12][13][14][15][16][17][18][19][20].Concerning the nonlinear dynamics of Alfvén modes (and its consequences on the overall performances of tokamak plasmas), it is determined by two main factors: the nonlinear wave-wave coupling and nonlinear waveparticle interactions. With reference to the former factor, various wave-wave interactions leading to the breaking of the Alfvénic state have been analyzed in [21,22]. Although these effects play a crucial role in multi-scale dynamics in burning plasmas, we will focus, in our current work, on the nonlinear wave-particle interactions. This issue has been first addressed withi...

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“…In this work, the BAAE is verified and studied through global gyrokinetic particle simulations for the first time using the gyrokinetic toroidal code (GTC). [13][14][15] GTC has been successfully applied to the kinetic study of the low frequency MHD modes such as geodesic acoustic mode (GAM), 16,17 BAE, [18][19][20] RSAE, 21 toroidal Alfven eigenmode (TAE), [22][23][24] energetic particle mode (EPM), 25 as well as current-driven MHD instabilities including internal kink mode 26 and resistive tearing mode. 27 In the current work, the existence of BAAE is first verified when ion temperature is much smaller than electron temperature (T i ( T e ) in the GTC simulations using initial perturbation, antenna excitation, and energetic particle excitation, separately.…”

Section: Introductionmentioning

confidence: 99%

Gyrokinetic particle simulation of beta-induced Alfven-acoustic eigenmode

et al. 2016

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The beta-induced Alfven-acoustic eigenmode (BAAE) in toroidal plasmas is verified and studied by global gyrokinetic particle simulations. When ion temperature is much lower than electron temperature, the existence of the weakly damped BAAE is verified in the simulations using initial perturbation, antenna excitation, and energetic particle excitation, respectively. When the ion temperature is comparable to the electron temperature, the unstable BAAE can be excited by realistic energetic particle density gradient, even though the stable BAAE (in the absence of energetic particles) is heavily damped by the thermal ions. In the simulations with reversed magnetic shear, BAAE frequency sweeping is observed and poloidal mode structure has a triangle shape with a poloidal direction similar to that observed in tokamak experiments. The triangle shape changes the poloidal direction, and no frequency sweeping is found in the simulations with normal magnetic shear. Published by AIP Publishing.

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Properties of toroidal Alfvén eigenmode in DIII-D plasma

Cited by 27 publications

References 55 publications

Gyrokinetic simulations of toroidal Alfvén eigenmodes excited by energetic ions and external antennas on the Joint European Torus

Gyrokinetic simulations of toroidal Alfvén eigenmodes excited by energetic ions and external antennas on the Joint European Torus

Saturation of single toroidal number Alfvén modes

Gyrokinetic particle simulation of beta-induced Alfven-acoustic eigenmode

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