Drift effects on electromagnetic geodesic acoustic modes
Abstract
A two fluid model with parallel viscosity is employed to derive the dispersion relation for electromagnetic geodesic acoustic modes (GAMs) in the presence of drift (diamagnetic) effects. Concerning the influence of the electron dynamics on the high frequency GAM, it is shown that the frequency of the electromagnetic GAM is independent of the equilibrium parallel current but, in contrast with purely electrostatic GAMs, significantly depends on the electron temperature gradient. The electromagnetic GAM may explain the discrepancy between the f ∼ 40 kHz oscillation observed in tokamak TCABR [Yu. K. Kuznetsov et al., Nucl. Fusion 52, 063044 (2012)] and the former prediction for the electrostatic GAM frequency. The radial wave length associated with this oscillation, estimated presently from this analytical model, is λ{sub r} ∼ 25 cm, i.e., an order of magnitude higher than the usual value for zonal flows (ZFs)
 Authors:
 Institute of Physics, University of São Paulo, São Paulo 05508900 (Brazil)
 Publication Date:
 OSTI Identifier:
 22408097
 Resource Type:
 Journal Article
 Resource Relation:
 Journal Name: Physics of Plasmas; Journal Volume: 22; Journal Issue: 2; Other Information: (c) 2015 AIP Publishing LLC; Country of input: International Atomic Energy Agency (IAEA)
 Country of Publication:
 United States
 Language:
 English
 Subject:
 70 PLASMA PHYSICS AND FUSION TECHNOLOGY; CURRENTS; DISPERSION RELATIONS; ELECTROMAGNETISM; ELECTRON TEMPERATURE; ELECTRONS; FLOW MODELS; GEODESICS; OSCILLATIONS; TCABR TOKAMAK; TEMPERATURE GRADIENTS; VISCOSITY
Citation Formats
Sgalla, R. J. F., Email: reneesgalla@gmail.com. Drift effects on electromagnetic geodesic acoustic modes. United States: N. p., 2015.
Web. doi:10.1063/1.4907196.
Sgalla, R. J. F., Email: reneesgalla@gmail.com. Drift effects on electromagnetic geodesic acoustic modes. United States. doi:10.1063/1.4907196.
Sgalla, R. J. F., Email: reneesgalla@gmail.com. 2015.
"Drift effects on electromagnetic geodesic acoustic modes". United States.
doi:10.1063/1.4907196.
@article{osti_22408097,
title = {Drift effects on electromagnetic geodesic acoustic modes},
author = {Sgalla, R. J. F., Email: reneesgalla@gmail.com},
abstractNote = {A two fluid model with parallel viscosity is employed to derive the dispersion relation for electromagnetic geodesic acoustic modes (GAMs) in the presence of drift (diamagnetic) effects. Concerning the influence of the electron dynamics on the high frequency GAM, it is shown that the frequency of the electromagnetic GAM is independent of the equilibrium parallel current but, in contrast with purely electrostatic GAMs, significantly depends on the electron temperature gradient. The electromagnetic GAM may explain the discrepancy between the f ∼ 40 kHz oscillation observed in tokamak TCABR [Yu. K. Kuznetsov et al., Nucl. Fusion 52, 063044 (2012)] and the former prediction for the electrostatic GAM frequency. The radial wave length associated with this oscillation, estimated presently from this analytical model, is λ{sub r} ∼ 25 cm, i.e., an order of magnitude higher than the usual value for zonal flows (ZFs)},
doi = {10.1063/1.4907196},
journal = {Physics of Plasmas},
number = 2,
volume = 22,
place = {United States},
year = 2015,
month = 2
}

By using the full electromagnetic drift kinetic equations for electrons and ions, the general dispersion relation for geodesic acoustic modes (GAMs) is derived incorporating the electromagnetic effects. It is shown that m = 1 harmonic of the GAM mode has a finite electromagnetic component. The electromagnetic corrections appear for finite values of the radial wave numbers and modify the GAM frequency. The effects of plasma pressure β{sub e}, the safety factor q, and the temperature ratio τ on GAM dispersion are analyzed.

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