Particle transport due to energetic-particle-driven geodesic acoustic modes

Zarzoso, D.; del‐Castillo‐Negrete, Diego; Escande, Dominique; Sarazin, Y.; Garbet, X.; Grandgirard, V.; Passeron, C.; Latu, Guillaume; Benkadda, S.

doi:10.1088/1741-4326/aad785

Cited by 12 publications

(22 citation statements)

References 41 publications

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“…10 and 11. The observed EGAM frequency 6,7 was found to be much smaller than the results of theoretical calculations 14,15 of the x EG -geodesic frequency driven by the beam, plasma parameters, and the angle between the magnetic field and NBI velocity. In the experiments, 6 the EGAM instabilities, driven by the counter NBI, were detected at a half minor radius and deeper, which is covered by the untrapped NBI region, but these types of instabilities are not observed 6 in the trapped ion region of higher radius positions 16 for the injected beam.…”

Section: Introductioncontrasting

confidence: 56%

Geodesic modes driven by untrapped resonances of NB energetic ions in tokamaks

2019

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Geodesic modes are typically excited by a minor concentration of energetic ions, but unstable mode frequencies are substantially different from Geodesic Acoustic Modes (GAMs) and are named EGAM (Energetic particle GAM). The EGAM instability driven by Neutral Beam Injection (NBI) has been observed in DIII-D tokamak experiments. The problem of the geodesic mode instability is analytically studied using a full drift kinetic equation. To analyze the instability condition, an ionization NBI location is assumed to be on the high field side of tokamaks. A minority NBI ion distribution is modeled by an energetic ion tail in the untrapped-passing region that remains between a magnetic axis and the trapped NBI boundary. The EGAM instability condition is defined by the parallel NBI ion velocity v||≈(1.2−1.5)ωR0q0 that has to be above the effective EGAM phase velocity. In this case, the EGAM frequency is ≈50% below the standard stable GAM frequency, which is reduced by a small concentration of energetic NBI ions. Qualitative comparison of the developed geodesic mode theory with NBI heating experiments in the midregion of the tokamak plasma is discussed.

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Section: Introductioncontrasting

confidence: 56%

Geodesic modes driven by untrapped resonances of NB energetic ions in tokamaks

2019

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“…It should be noted here that in contrast to finite-n modes (where n is a toroidal number), which also can transfer energy from the EPs to the thermal plasma due to the wave-particle interaction, the EGAM dynamics is practically not associated with additional particle loss, at least if one does not consider the mode propagation and topological orbital changes 23 .…”

Section: Introductionmentioning

confidence: 99%

Nonlinear dynamics of energetic-particle driven geodesic acoustic modes in ASDEX Upgrade

et al. 2020

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Turbulence in tokamaks generates radially sheared zonal flows (ZFs). Their oscillatory counterparts, geodesic acoustic modes (GAMs), appear due to the action of the magnetic field curvature. The GAMs can also be driven unstable by an anisotropic energetic particle (EP) population leading to the formation of global radial structures, called EGAMs. The EGAMs might play the role of an intermediate agent between the EPs and thermal plasma, by redistributing EP energy to the bulk plasma through collisionless wave-particle interaction. In such a way, the EGAMs might contribute to the plasma heating. Thus, investigation of EGAM properties, especially in the velocity space, is necessary for precise understanding of the transport phenomena in tokamak plasmas. In this work, the nonlinear dynamics of EGAMs is investigated with the help of a Mode-Particle-Resonance (MPR) diagnostic recently implemented in the global gyrokinetic (GK) particle-in-cell code ORB5. This enables to investigate the relative importance and the evolution of the resonances responsible for the ion and electron Landau damping, and of the EP drive. An ASDEX Upgrade discharge is chosen as a reference case for this investigation due to its rich EP nonlinear dynamics.

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“…Furthermore, fast particle losses can damage the plasma facing components and thus limit the operating life of the internal wall. Energetic particles can also excite the so-called energetic particle driven modes (EPM) which can increase the energetic particle transport from the core to the edge of the tokamak resulting eventually in significant losses, even in the presence of one single electrostatic mode [1]. In addition, steep pressure profiles lead to microinstabilities, which in nonlinear phase result in microturbulence.…”

Section: Introductionmentioning

confidence: 99%

Impact of fast ions on a trapped-electron-mode dominated plasma in a JT-60U hybrid scenario

Mazzi¹,

Zarzoso²,

García³

et al. 2020

Nucl. Fusion

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The impact of fast ions on a trapped electron mode (TEM) is extensively analysed by linear and nonlinear gyrokinetic simulations for a JT-60U plasma at high β and low magnetic shear using the Gene code in local approximation. For the first time, it is shown that TEM-induced turbulent transport may remain unaffected by the steep fast ion pressure profile generated by the Neutral Beam Injection. Unlike recent observations of ion temperature gradient (ITG)-induced turbulent transport reductions due to fast ions, TEMdominated systems could act differently in the presence of a significant fast ion population. The possible role of zonal flows as a saturation mechanism is analyzed, showing that their weak impact in the reported JT-60U scenario might lead to different behaviour of fast ions with respect to the ITG-dominated discharges. It is also shown that Alfvénic shear modes are destabilized at low wave numbers (n 8). They are identified as drift Alfvén waves destabilized by ITG, which is a form of Alfvénic ITG instabilities. Deep numerical analysis provides the physical parameter range in which ITG-driven BAEs are stabilized. These results open the way to new possibilities of tailoring future experimental scenarios in order to benefit from transport reduction by fast ions.

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Particle transport due to energetic-particle-driven geodesic acoustic modes

Cited by 12 publications

References 41 publications

Geodesic modes driven by untrapped resonances of NB energetic ions in tokamaks

Geodesic modes driven by untrapped resonances of NB energetic ions in tokamaks

Nonlinear dynamics of energetic-particle driven geodesic acoustic modes in ASDEX Upgrade

Impact of fast ions on a trapped-electron-mode dominated plasma in a JT-60U hybrid scenario

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