Geodesic acoustic mode frequency and the structure of Alfvén continuum in toroidal plasmas with highq2β

Fesenyuk, O. P.; Kolesnichenko, Ya. I.; Yakovenko, Yu. V.

doi:10.1088/0741-3335/54/8/085014

Cited by 18 publications

(28 citation statements)

References 23 publications

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“…The equation above shows that for poloidal fluid perturbations, the harmonic n m couples with the harmonics n mÀ2 and n mþ2 as described in Ref. 29. It indicates that the presence of toroidal rotational flow does not play a qualitative role in mode coupling but introduces quantitative and also remarkable corrections.…”

Section: Linearized Equationsmentioning

confidence: 68%

“…21 EPs are shown to drive GAMs based on both experimental results [22][23][24] and theoretical exploration. 19,[25][26][27][28] Recently, Fesenyuk et al 29 investigated the GAM associated with the structure of Alfv en continuum in toroidal plasmas with high q 2 b using the mode equations derived almost ten years ago. 30 Owing to the significant applications to theẼ ÂB shear flow control of anomalous transport and turbulence, the magnitude, radial profile, and evolution of the toroidal flow in tokamak plasmas have been important issues in tokamaks.…”

Section: Introductionmentioning

confidence: 99%

“…That is the scope and objective of the present work which is motivated by Ref. 29. It should be noted that the EPRF is not taken into account in our model since it is less than the ETRF by at least one order of magnitude as shown below.…”

Section: Introductionmentioning

confidence: 99%

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Geodesic acoustic modes in toroidally rotating tokamaks with an arbitrary β

Ren

Chu

2013

Physics of Plasmas

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Theoretical research on the geodesic acoustic mode (GAM) induced by the equilibrium toroidal rotation flow (ETRF) in the tokamak plasmas with an arbitrary b is performed by using the ideal magnetohydrodynamic model, where b is the ratio of the plasma pressure and magnetic field pressure. Two equations determining the poloidal displacement n h and the divergence of the Lagrangian perturbation are obtained and suitable for arbitrary cross-section tokamaks with largeaspect-ratios. The dispersion relations are then derived for two different coupling patterns by assuming n 62 ¼ 0 and n 64 ¼ 0, respectively, where n m ¼ 1 2p Þ n h e imh dh with h being the poloidal angle under the circular cross-section condition. In both patterns, the ETRF will increase the frequencies of the GAMs but b can decrease them. The GAM for n 62 ¼ 0 has a larger frequency than GAM for n 64 ¼ 0.

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Section: Linearized Equationsmentioning

confidence: 68%

Section: Introductionmentioning

confidence: 99%

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Geodesic acoustic modes in toroidally rotating tokamaks with an arbitrary β

Ren

Chu

2013

Physics of Plasmas

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“…, where c s is the sound velocity, v A is the Alfvén velocity, and q is the tokamak safety factor [9,10]. This was the case in the mentioned DIII-D experiment where β ∼ 0.4% [6].…”

mentioning

confidence: 88%

Manifestations of the geodesic acoustic mode driven by energetic ions in tokamaks

Kolesnichenko

Lutsenko

Yakovenko

et al. 2016

Plasma Phys. Control. Fusion

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Effects of the energetic-ion-driven Geodesic Acoustic modes (GAM and E-GAM) on the toroidally passing energetic ions and the concomitant change of the neutron yield of beam-plasma fusion reactions in tokamaks are considered. It is shown that due to large perturbations of the plasma density, the resonant energetic ions driving the instability can be considerably slowed down for a few tens of the particle transit periods, which is much less than the collisional slowing down time. The time of the collisionless slowing down is actually determined by the period of the particle motion within the resonance island arising because of the GAM / E-GAM. Being trapped in the island, the resonant particles can not only lose their energy but also gain it. One more effect of GAMs is the flattening on the distribution function of the resonant particles. Due to conservation of the canonical angular momentum during a GAM / E-GAM instability, the change of the particle energy is accompanied by a radial displacement of the resonant particle for a distance up to the poloidal Larmor radius of energetic ions. The particles are displaced inwards or outwards, depending on the direction of their motion along the magnetic field. Expressions describing the change of the neutron yield due to GAM modes are derived. It is found that the distortion of the velocity distribution of the resonant particles can lead to a considerable drop of the neutron emission even when effects of the particle radial displacement are small. The developed theory is applied to an E-GAM experiment on the DIII-D tokamak. Relations for the period of the motion within the resonance island of passing (both well passing and marginally passing) particles and the width of the resonance of the energetic particles with GAM modes and low-frequency Alfvén modes are derived.

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“…This effect can be taken into account by assuming R ω > R. On the other hand, the plasma compressibility (which produces the low frequency β-induced gap) tends to shift gaps in the AC up. This effect seems weak in stellarators but can be very strong in spherical tokamaks and in conventional tokamaks with hollow current when β > ι 2 (β = 8πp/B 2 , p is the plasma pressure) [13].…”

Section: Resonances Between Particles and Alfvén Gap Modesmentioning

confidence: 99%

Landau damping of Alfvénic modes in stellarators

Kolesnichenko¹,

Tykhyy²

2018

Plasma Phys. Control. Fusion

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It is found that the presence of the so-called non-axisymmetric resonances of wave-particle interaction in stellarators [which are associated with the lack of axial symmetry of the magnetic configuration, Kolesnichenko et al., Phys. Plasmas 9 (2002) 517 ] may have a strong stabilizing influence through Landau mechanism on the Toroidicity-induced Alfvén Eigenmodes (TAE) and isomon modes (Alfvénic modes with equal poloidal and toroidal mode numbers and frequencies in the continuum region) destabilized by the energetic ions. These resonances involve largest harmonics of the equilibrium magnetic field of stellarators and lead to absorption of the mode energy by thermal ions in medium pressure plasma, in which case the effect is large. On the other hand, at the high pressure attributed to, e.g., a Helias reactor, thermal ions can interact also with high frequency Alfvén gap modes [Helicity-induced Alfvén Eigenmodes (HAE) and mirror-induced Alfvén Eigenmodes (MAE)], leading to a considerable damping of these modes. Only resonances with passing particles are considered. The developed theory is applied to various modes in the Wendelstein 7-X stellarator and a Helias reactor, and to two TAE modes in the LHD helical device.

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Geodesic acoustic mode frequency and the structure of Alfvén continuum in toroidal plasmas with highq²β

Cited by 18 publications

References 23 publications

Geodesic acoustic modes in toroidally rotating tokamaks with an arbitrary β

Geodesic acoustic modes in toroidally rotating tokamaks with an arbitrary β

Manifestations of the geodesic acoustic mode driven by energetic ions in tokamaks

Landau damping of Alfvénic modes in stellarators

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