Drift effects on electromagnetic geodesic acoustic modes

Sgalla, R J F

doi:10.1063/1.4907196

Cited by 5 publications

(8 citation statements)

References 56 publications

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“…Another direction to improve our present theory is to include more physics such as diamagnetic drifts due to density and temperature gradients that are not considered here. It has been shown within the two-fluid model that these effects split the local GAM into several branches [24,25]. When extending these local mode theories to the global ones, adopting the recipe in this paper, we may explain multiple global GAMs observed in experiments [9,14].…”

Section: Conclusion and Discussionmentioning

confidence: 82%

“…The frequency of the global GAM will be considered to be of the same order as that of the local GAM given by equation (25), i.e.…”

Section: The Ordering Prescription For Electromagnetic Perturbationsmentioning

confidence: 99%

“…which is equation ( 21), one of the key equations that leads to the local GAM dispersion relation (25). This is why the global GAM is allowed to have a big geodesic displacement that is almost independent of θ.…”

Section: Balance Of Second θ-Harmonics Via the Electro Magnetic Pertu...mentioning

confidence: 99%

“…At first, some monotonically decreasing temperature profile will be combined with a certain q-profile that has a relatively long range of negative slope in the inner half part of the plasma column, to produce the Ω 2 g (r) profile that has an off-axis global maximum in this region, according to equation (25).…”

Section: The Solution In the Inner Regionmentioning

confidence: 99%

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Global MHD GAMs in toroidal plasmas with reversed magnetic shear

Zhou

Wang

2018

Nucl. Fusion

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A formalism is developed for axisymmetric (n = 0) perturbations of toroidal plasmas in the framework of ideal magnetohydrodynamics, and is applied successfully to the explanation of the global structures of geodesic acoustic modes (GAMs) that have been revealed by the numerical simulations of tokamak plasmas with an off-axis maximum of local GAM frequency. It turns out that the global structures of GAM can emerge as the consequence of balancing the momenta associated with the second poloidal harmonics introduced by the coupling between the curvatures of equilibrium magnetic field lines and the pressure perturbations via Alfvénic perturbations. The global GAM frequency is allowed to reside in the narrow gap between the maxima of the modified local GAM frequencies due to Alfvénic perturbations. This mode features a distinct ‘singular’ layer centered around the local GAM maxima, where both the acoustic/geodesic acoustic and Alfvénic perturbations are equally important and the eigenfunction resembles the symbol . This layer is sandwiched between two wider regions where the Alfvénic activities dominate. The negative magnetic shear plays an indispensable role in establishing the global mode structures, in that it shapes the eigenfunctions in the right way in the outer regions and allows them to match with the inner segment smoothly. Many features of the global GAM predicted by our theory are confirmed by running our shooting code for both weakly and strongly reversed magnetic shear profiles.

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Section: Conclusion and Discussionmentioning

confidence: 82%

“…The frequency of the global GAM will be considered to be of the same order as that of the local GAM given by equation (25), i.e.…”

Section: The Ordering Prescription For Electromagnetic Perturbationsmentioning

confidence: 99%

Section: Balance Of Second θ-Harmonics Via the Electro Magnetic Pertu...mentioning

confidence: 99%

Section: The Solution In the Inner Regionmentioning

confidence: 99%

See 2 more Smart Citations

Global MHD GAMs in toroidal plasmas with reversed magnetic shear

Zhou

Wang

2018

Nucl. Fusion

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“…Researchers found that the two-fluid model could be able to give a solution to this question. Such a discrepancy has shown to be removed on the leading order by taking into account the anisotropic ion parallel viscosity in the two-fluid equations [9][10][11][12]. It was also discussed in detail by Storelli et al [13].…”

mentioning

confidence: 89%

Geodesic acoustic mode in a reduced two-fluid model

Ren

2017

Plasma Sci. Technol.

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A reduced two-fluid model is constructed to investigate the geodesic acoustic mode (GAM). The ion dynamics is sufficiently considered by including an anisotropic pressure tensor and inhibited heat flux vector, whose evolutions are determined by equations derived from the 16-momentum model. Electrons are supposed to obey the Boltzmann distribution responding to the electrostatic oscillation with near ion acoustic velocity. In the large safety factor limit, the GAM frequency is identical with the kinetic one to the order of q 1 2 when zeroing the anisotropy. For general anisotropy, the reduced two-fluid model generates the frequency agreeing well with the kinetic result with arbitrary electron temperature. The present simplified fluid model will be of great use and interest for young researchers and students devoted to plasma physics.

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Electromagnetic effect on geodesic acoustic mode with adiabatic electrons

Huang

Ren

2019

Physics of Plasmas

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The geodesic acoustic mode (GAM) is analytically investigated by taking into account the finite-orbit-width (FOW) resonance effect to the second order and the finite β effect. The general dispersion relation is derived from the gyro-kinetic equations in the presence of nonzero δA∥, the parallel component of the perturbed magnetic vector potential. Transparent and concise expressions for the GAM frequency and Landau damping rate in the presence of the second order FOW effect and finite β effect are first presented. It is clearly shown that the m = ±2 harmonics dominant δA∥ and the kinetic expression of δA∥ have the same form as the fluid one. For the real frequency, the electromagnetic effect introduces a term on the order of q2β, which is comparable to the second order electrostatic terms, namely, the terms introduced by the second order FOW resonance effect. While for the collisionless damping rate, δA∥ does not directly introduce β–dependent terms, but affects the damping rate via modifying the real frequency. Besides, our analytical result shows good agreement with the numerical examinations.

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Drift effects on electromagnetic geodesic acoustic modes

Cited by 5 publications

References 56 publications

Global MHD GAMs in toroidal plasmas with reversed magnetic shear

Global MHD GAMs in toroidal plasmas with reversed magnetic shear

Geodesic acoustic mode in a reduced two-fluid model

Electromagnetic effect on geodesic acoustic mode with adiabatic electrons

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