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Description of global EGAM in the maximum of local frequency during current ramp-up discharges in DIII-D

Published online by Cambridge University Press:  09 June 2022

F. Camilo de Souza Open the ORCID record for F. Camilo de Souza [Opens in a new window] ,
N. Gorelenkov ,
A. Elfimov ,
R. Galvão ,
C. Collins ,
M. Podesta  and
E. Fredrickson
F. Camilo de Souza*
Affiliation:
Institute of Physics, University of São Paulo, São Paulo, Brazil
N. Gorelenkov
Affiliation:
Princeton Plasma Physics Laboratory, Princeton, NJ USA
A. Elfimov
Affiliation:
Institute of Physics, University of São Paulo, São Paulo, Brazil
R. Galvão
Affiliation:
Institute of Physics, University of São Paulo, São Paulo, Brazil
C. Collins
Affiliation:
General Atomics, San Diego, CA, USA
M. Podesta
Affiliation:
Princeton Plasma Physics Laboratory, Princeton, NJ USA
E. Fredrickson
Affiliation:
Princeton Plasma Physics Laboratory, Princeton, NJ USA
*
†Email address for correspondence: fabio.camilo.souza@usp.br
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Abstract

Energetic-particle-induced geodesic acoustic modes, EGAMs (Fu, Phys. Rev. Let., vol. 101, 2008, pp. 185002), driven by neutral beam injection (NBI), have been observed in many DIII-D tokamak experiments (Nazikian et al., Phys. Rev. Lett., vol. 101, 2008, pp. 185001). This mechanism has been theoretically investigated in (Qiu et al., Plasma Phys. Control. Fusion, vol. 52, 2010, pp. 095003), using a sharp energetic particle distribution function, and in (Qu et al., Plasma Phys. Control. Fusion, vol. 59, 2017, pp. 055018), where the dispersion relation and eigenmode behaviour were obtained for the situation of early beam scenario, that is, for times smaller than the beam slowing down time. In this work, we extend these studies determining the eigenmode for beyond the slowing down time, in a scenario with reverse safety factor $q$ profile, where a small concentration of energetic ions can produce an off-axis maximum in the GAM dispersion relation. The characteristics of EGAM are analytically studied with the drift kinetic equation together with the MHD code NOVA. The toroidal energetic ion transit frequency, coupled with the GAM frequency, produces the maximum in the dispersion relation where the eigenmode can be found. The quantitative correspondence of experimental results with the predictions of the proposed model is analysed.

Keywords

fusion plasmaplasma instabilitiesplasma waves
Type
Research Article
Information
Journal of Plasma Physics , Volume 88 , Issue 3 , June 2022 , 905880308
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Copyright
Copyright © The Author(s), 2022. Published by Cambridge University Press

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Footnotes

‡

deceased.

References

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